1
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Wang L, Yan X, Min J, Sun D, Xie X, Peng SG, Zhan M, Jiang K. Scale Invariance of a Spherical Unitary Fermi Gas. PHYSICAL REVIEW LETTERS 2024; 132:243403. [PMID: 38949354 DOI: 10.1103/physrevlett.132.243403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 04/06/2024] [Accepted: 05/21/2024] [Indexed: 07/02/2024]
Abstract
A unitary Fermi gas in an isotropic harmonic trap is predicted to show scale and conformal symmetry that have important consequences in its thermodynamic and dynamical properties. By experimentally realizing a unitary Fermi gas in an isotropic harmonic trap, we demonstrate its universal expansion dynamics along each direction and at different temperatures. We show that as a consequence of SO(2,1) symmetry, the measured release energy is equal to that of the trapping energy. We further observe the breathing mode with an oscillation frequency twice the trapping frequency and a small damping rate, providing the evidence of SO(2,1) symmetry. In addition, away from resonance when scale invariance is broken, we determine the effective exponent γ that relates the chemical potential and average density along the BEC-BCS crossover, which qualitatively agrees with the mean field predictions. This Letter opens the possibility of studying nonequilibrium dynamics in a conformal invariant system in the future.
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Affiliation(s)
| | - Xiangchuan Yan
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
| | | | - Dali Sun
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
| | | | - Shi-Guo Peng
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
| | - Mingsheng Zhan
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
| | - Kaijun Jiang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
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2
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Gawryluk K, Brewczyk M. Mechanism for sound dissipation in a two-dimensional degenerate Fermi gas. Sci Rep 2024; 14:10815. [PMID: 38734745 PMCID: PMC11088693 DOI: 10.1038/s41598-024-61521-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 05/07/2024] [Indexed: 05/13/2024] Open
Abstract
We numerically study the transport properties of a two-dimensional Fermi gas in a weakly and strongly interacting regimes, in the range of temperatures close to the transition to a superfluid phase. For that we excite sound waves in a fermionic mixture by using the phase imprinting technique, follow their evolution, and finally determine both their speed and attenuation. Our formalism, originated from a density-functional theory, incorporates thermal fluctuations via the grand canonical ensemble description and with the help of Metropolis algoritm. From numerical simulations we extract temperature dependence of the sound velocity and diffusivity as well as the dependence on the interaction strength. We emphasize the role of virtual vortex-antivortex pairs creation in the process of sound dissipation.
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Affiliation(s)
- Krzysztof Gawryluk
- Wydział Fizyki, Uniwersytet w Białymstoku, ul. K. Ciołkowskiego 1L, 15245, Białystok, Poland.
| | - Mirosław Brewczyk
- Wydział Fizyki, Uniwersytet w Białymstoku, ul. K. Ciołkowskiego 1L, 15245, Białystok, Poland
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3
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Fabritius P, Mohan J, Talebi M, Wili S, Zwerger W, Huang MZ, Esslinger T. Irreversible entropy transport enhanced by fermionic superfluidity. NATURE PHYSICS 2024; 20:1091-1096. [PMID: 39036649 PMCID: PMC11254751 DOI: 10.1038/s41567-024-02483-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 03/20/2024] [Indexed: 07/23/2024]
Abstract
The nature of particle and entropy flow between two superfluids is often understood in terms of reversible flow carried by an entropy-free, macroscopic wavefunction. While this wavefunction is responsible for many intriguing properties of superfluids and superconductors, its interplay with excitations in non-equilibrium situations is less understood. Here we observe large concurrent flows of both particles and entropy through a ballistic channel connecting two strongly interacting fermionic superfluids. Both currents respond nonlinearly to chemical potential and temperature biases. We find that the entropy transported per particle is much larger than the prediction of superfluid hydrodynamics in the linear regime and largely independent of changes in the channel's geometry. By contrast, the timescales of advective and diffusive entropy transport vary significantly with the channel geometry. In our setting, superfluidity counterintuitively increases the speed of entropy transport. Moreover, we develop a phenomenological model describing the nonlinear dynamics within the framework of generalized gradient dynamics. Our approach for measuring entropy currents may help elucidate mechanisms of heat transfer in superfluids and superconducting devices.
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Affiliation(s)
- Philipp Fabritius
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Jeffrey Mohan
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Mohsen Talebi
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Simon Wili
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Wilhelm Zwerger
- Physik Department, Technische Universität München, Garching, Germany
| | - Meng-Zi Huang
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Tilman Esslinger
- Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland
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4
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Yan Z, Patel PB, Mukherjee B, Vale CJ, Fletcher RJ, Zwierlein MW. Thermography of the superfluid transition in a strongly interacting Fermi gas. Science 2024; 383:629-633. [PMID: 38330124 DOI: 10.1126/science.adg3430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Accepted: 01/10/2024] [Indexed: 02/10/2024]
Abstract
Heat transport can serve as a fingerprint identifying different states of matter. In a normal liquid, a hotspot diffuses, whereas in a superfluid, heat propagates as a wave called "second sound." Direct imaging of heat transport is challenging, and one usually resorts to detecting secondary effects. In this study, we establish thermography of a strongly interacting atomic Fermi gas, whose radio-frequency spectrum provides spatially resolved thermometry with subnanokelvin resolution. The superfluid phase transition was directly observed as the sudden change from thermal diffusion to second-sound propagation and is accompanied by a peak in the second-sound diffusivity. This method yields the full heat and density response of the strongly interacting Fermi gas and therefore all defining properties of Landau's two-fluid hydrodynamics.
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Affiliation(s)
- Zhenjie Yan
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Parth B Patel
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Biswaroop Mukherjee
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Chris J Vale
- Optical Science Centre and ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Swinburne University of Technology, Melbourne 3122, Australia
| | - Richard J Fletcher
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Martin W Zwierlein
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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5
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Dagar G, Kumar R, Yadav KK, Singh M, Pandita TK. Ubiquitination and deubiquitination: Implications on cancer therapy. BIOCHIMICA ET BIOPHYSICA ACTA. GENE REGULATORY MECHANISMS 2023; 1866:194979. [PMID: 37633647 DOI: 10.1016/j.bbagrm.2023.194979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 07/28/2023] [Accepted: 08/21/2023] [Indexed: 08/28/2023]
Abstract
The ubiquitin proteasomal system (UPS) represents a highly regulated protein degradation pathway essential for maintaining cellular homeostasis. This system plays a critical role in several cellular processes, which include DNA damage repair, cell cycle checkpoint control, and immune response regulation. Recently, the UPS has emerged as a promising target for cancer therapeutics due to its involvement in oncogenesis and tumor progression. Here we aim to summarize the key aspects of the UPS and its significance in cancer therapeutics. We begin by elucidating the fundamental components of the UPS, highlighting the role of ubiquitin, E1-E3 ligases, and the proteasome in protein degradation. Furthermore, we discuss the intricate process of ubiquitination and proteasomal degradation, emphasizing the specificity and selectivity achieved through various signaling pathways. The dysregulation of the UPS has been implicated in cancer development and progression. Aberrant ubiquitin-mediated degradation of key regulatory proteins, such as tumor suppressors and oncoproteins, can lead to uncontrolled cell proliferation, evasion of apoptosis, and metastasis. We outline the pivotal role of the UPS in modulating crucial oncogenic pathways, including the regulation of cyclins, transcription factors, Replication stress components and DNA damage response. The increasing recognition of the UPS as a target for cancer therapeutics has spurred the development of small molecules, peptides, and proteasome inhibitors with the potential to restore cellular balance and disrupt tumor growth. We provide an overview of current therapeutic strategies aimed at exploiting the UPS, including the use of proteasome inhibitors, deubiquitinating enzyme inhibitors, and novel E3 ligase modulators. We further discuss novel emerging strategies for the development of next-generation drugs that target proteasome inhibitors. Exploiting the UPS for cancer therapeutics offers promising avenues for developing innovative and effective treatment strategies, providing hope for improved patient outcomes in the fight against cancer.
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Affiliation(s)
- Gunjan Dagar
- Department of Medical Oncology, Dr BRAIRCH, All India Institute of Medical Sciences, New Delhi 110029, India
| | - Rakesh Kumar
- School of Biotechnology, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir 182320, India.
| | - Kamlesh K Yadav
- Center for Genomics and Precision Medicine, Texas A&M College of Medicine, Houston, TX 77030, USA; School of Engineering Medicine, Texas A&M University, School of Medicine, Houston, TX 77030, USA.
| | - Mayank Singh
- Department of Medical Oncology, Dr BRAIRCH, All India Institute of Medical Sciences, New Delhi 110029, India.
| | - Tej K Pandita
- Center for Genomics and Precision Medicine, Texas A&M College of Medicine, Houston, TX 77030, USA.
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6
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Chauveau G, Maury C, Rabec F, Heintze C, Brochier G, Nascimbene S, Dalibard J, Beugnon J, Roccuzzo SM, Stringari S. Superfluid Fraction in an Interacting Spatially Modulated Bose-Einstein Condensate. PHYSICAL REVIEW LETTERS 2023; 130:226003. [PMID: 37327429 DOI: 10.1103/physrevlett.130.226003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 04/07/2023] [Accepted: 05/09/2023] [Indexed: 06/18/2023]
Abstract
At zero temperature, a Galilean-invariant Bose fluid is expected to be fully superfluid. Here we investigate theoretically and experimentally the quenching of the superfluid density of a dilute Bose-Einstein condensate due to the breaking of translational (and thus Galilean) invariance by an external 1D periodic potential. Both Leggett's bound fixed by the knowledge of the total density and the anisotropy of the sound velocity provide a consistent determination of the superfluid fraction. The use of a large-period lattice emphasizes the important role of two-body interactions on superfluidity.
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Affiliation(s)
- G Chauveau
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - C Maury
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - F Rabec
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - C Heintze
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - G Brochier
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - S Nascimbene
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - J Dalibard
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - J Beugnon
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - S M Roccuzzo
- Pitaevskii BEC Center, CNR-INO and Dipartimento di Fisica, Università di Trento, I-38123 Trento, Italy and Trento Institute for Fundamental Physics and Applications, INFN, 38123 Trento, Italy
| | - S Stringari
- Pitaevskii BEC Center, CNR-INO and Dipartimento di Fisica, Università di Trento, I-38123 Trento, Italy and Trento Institute for Fundamental Physics and Applications, INFN, 38123 Trento, Italy
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7
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Hilker TA, Dogra LH, Eigen C, Glidden JAP, Smith RP, Hadzibabic Z. First and Second Sound in a Compressible 3D Bose Fluid. PHYSICAL REVIEW LETTERS 2022; 128:223601. [PMID: 35714252 DOI: 10.1103/physrevlett.128.223601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 04/12/2022] [Indexed: 06/15/2023]
Abstract
The two-fluid model is fundamental for the description of superfluidity. In the nearly incompressible liquid regime, it successfully describes first and second sound, corresponding, respectively, to density and entropy waves, in both liquid helium and unitary Fermi gases. Here, we study the two sounds in the opposite regime of a highly compressible fluid, using an ultracold ^{39}K Bose gas in a three-dimensional box trap. We excite the longest-wavelength mode of our homogeneous gas, and observe two distinct resonant oscillations below the critical temperature, of which only one persists above it. In a microscopic mode-structure analysis, we find agreement with the hydrodynamic theory, where first and second sound involve density oscillations dominated by, respectively, thermal and condensed atoms. Varying the interaction strength, we explore the crossover from hydrodynamic to collisionless behavior in a normal gas.
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Affiliation(s)
- Timon A Hilker
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Lena H Dogra
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Christoph Eigen
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Jake A P Glidden
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Robert P Smith
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Zoran Hadzibabic
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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8
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Li X, Luo X, Wang S, Xie K, Liu XP, Hu H, Chen YA, Yao XC, Pan JW. Second sound attenuation near quantum criticality. Science 2022; 375:528-533. [PMID: 35113717 DOI: 10.1126/science.abi4480] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Second sound attenuation, a distinctive dissipative hydrodynamic phenomenon in a superfluid, is crucial for understanding superfluidity and elucidating critical phenomena. Here, we report the observation of second sound attenuation in a homogeneous Fermi gas of lithium-6 atoms at unitarity by performing Bragg spectroscopy with high energy resolution in the long-wavelength limit. We successfully obtained the temperature dependence of second sound diffusivity [Formula: see text] and thermal conductivity κ. Furthermore, we observed a sudden rise-a precursor of critical divergence-in both [Formula: see text] and κ at a temperature of about 0.95 superfluid transition temperature [Formula: see text]. This suggests that the unitary Fermi gas has a much larger critical region than does liquid helium. Our results pave the way for determining the universal critical scaling functions near quantum criticality.
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Affiliation(s)
- Xi Li
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Xiang Luo
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Shuai Wang
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Ke Xie
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Xiang-Pei Liu
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Hui Hu
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Centre for Quantum Technology Theory, Swinburne University of Technology, Melbourne, VIC 3122, Australia
| | - Yu-Ao Chen
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Xing-Can Yao
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Jian-Wei Pan
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.,Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.,Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
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9
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Hoffmann DK, Singh VP, Paintner T, Jäger M, Limmer W, Mathey L, Hecker Denschlag J. Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid. Nat Commun 2021; 12:7074. [PMID: 34873169 PMCID: PMC8648831 DOI: 10.1038/s41467-021-27149-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 10/26/2021] [Indexed: 11/28/2022] Open
Abstract
Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid, extending previous work at unitarity. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation in the crossover. Working with a quantum gas of ultracold fermionic 6Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. By varying the excitation procedure, we gain deeper insight on sound propagation. We compare our measurement results with classical-field simulations, which help with the interpretation of our experiments.
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Affiliation(s)
- Daniel K Hoffmann
- Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany
| | - Vijay Pal Singh
- Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstraße 2, 30167, Hannover, Germany
- Institut für Laserphysik, Zentrum für Optische Quantentechnologien, Universität Hamburg, 22761, Hamburg, Germany
| | - Thomas Paintner
- Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany
| | - Manuel Jäger
- Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany
| | - Wolfgang Limmer
- Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany
| | - Ludwig Mathey
- Institut für Laserphysik, Zentrum für Optische Quantentechnologien, Universität Hamburg, 22761, Hamburg, Germany
- The Hamburg center for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
| | - Johannes Hecker Denschlag
- Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany.
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10
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Christodoulou P, Gałka M, Dogra N, Lopes R, Schmitt J, Hadzibabic Z. Observation of first and second sound in a BKT superfluid. Nature 2021; 594:191-194. [PMID: 34108696 DOI: 10.1038/s41586-021-03537-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 04/12/2021] [Indexed: 02/05/2023]
Abstract
Superfluidity in its various forms has been of interest since the observation of frictionless flow in liquid helium II1,2. In three spatial dimensions it is conceptually associated with the emergence of long-range order at a critical temperature. One of the hallmarks of superfluidity, as predicted by the two-fluid model3,4 and observed in both liquid helium5 and in ultracold atomic gases6,7, is the existence of two kinds of sound excitation-the first and second sound. In two-dimensional systems, thermal fluctuations preclude long-range order8,9; however, superfluidity nevertheless emerges at a non-zero critical temperature through the infinite-order Berezinskii-Kosterlitz-Thouless (BKT) transition10,11, which is associated with a universal jump12 in the superfluid density without any discontinuities in the thermodynamic properties of the fluid. BKT superfluids are also predicted to support two sounds, but so far this has not been observed experimentally. Here we observe first and second sound in a homogeneous two-dimensional atomic Bose gas, and use the two temperature-dependent sound speeds to determine the superfluid density of the gas13-16. Our results agree with the predictions of BKT theory, including the prediction of a universal jump in the superfluid density at the critical temperature.
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Affiliation(s)
| | - Maciej Gałka
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Nishant Dogra
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Raphael Lopes
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL Research University, Sorbonne Université, Paris, France
| | - Julian Schmitt
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.,Institut für Angewandte Physik, Universität Bonn, Bonn, Germany
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11
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Berezinskii-Kosterlitz-Thouless phase induced by dissipating quasisolitons. Sci Rep 2021; 11:10773. [PMID: 34031458 PMCID: PMC8144421 DOI: 10.1038/s41598-021-90169-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 05/05/2021] [Indexed: 11/08/2022] Open
Abstract
We theoretically study the sound propagation in a two-dimensional weakly interacting uniform Bose gas. Using the classical fields approximation we analyze in detail the properties of density waves generated both in a weak and strong perturbation regimes. While in the former case density excitations can be described in terms of hydrodynamic or collisionless sound, the strong disturbance of the system results in a qualitatively different response. We identify observed structures as quasisolitons and uncover their internal complexity for strong perturbation case. For this regime quasisolitons break into vortex pairs as time progresses, eventually reaching an equilibrium state. We find this state, characterized by only fluctuating in time averaged number of pairs of opposite charge vortices and by appearance of a quasi-long-range order, as the Berezinskii-Kosterlitz-Thouless (BKT) phase.
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12
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Del Pace G, Kwon WJ, Zaccanti M, Roati G, Scazza F. Tunneling Transport of Unitary Fermions across the Superfluid Transition. PHYSICAL REVIEW LETTERS 2021; 126:055301. [PMID: 33605753 DOI: 10.1103/physrevlett.126.055301] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 01/12/2021] [Indexed: 06/12/2023]
Abstract
We investigate the transport of a Fermi gas with unitarity-limited interactions across the superfluid phase transition, probing its response to a direct current (dc) drive through a tunnel junction. As the superfluid critical temperature is crossed from below, we observe the evolution from a highly nonlinear to an Ohmic conduction characteristic, associated with the critical breakdown of the Josephson dc current induced by pair condensate depletion. Moreover, we reveal a large and dominant anomalous contribution to resistive currents, which reaches its maximum at the lowest attained temperature, fostered by the tunnel coupling between the condensate and phononic Bogoliubov-Anderson excitations. Increasing the temperature, while the zeroing of supercurrents marks the transition to the normal phase, the conductance drops considerably but remains much larger than that of a normal, uncorrelated Fermi gas tunneling through the same junction. We attribute such enhanced transport to incoherent tunneling of sound modes, which remain weakly damped in the collisional hydrodynamic fluid of unpaired fermions at unitarity.
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Affiliation(s)
- G Del Pace
- Department of Physics and Astronomy, University of Florence, 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
| | - W J Kwon
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
| | - M Zaccanti
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
| | - G Roati
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
| | - F Scazza
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
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13
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Patel PB, Yan Z, Mukherjee B, Fletcher RJ, Struck J, Zwierlein MW. Universal sound diffusion in a strongly interacting Fermi gas. Science 2021; 370:1222-1226. [PMID: 33273102 DOI: 10.1126/science.aaz5756] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 10/24/2020] [Indexed: 11/02/2022]
Abstract
Transport of strongly interacting fermions is crucial for the properties of modern materials, nuclear fission, the merging of neutron stars, and the expansion of the early Universe. Here, we observe a universal quantum limit of diffusivity in a homogeneous, strongly interacting atomic Fermi gas by studying sound propagation and its attenuation through the coupled transport of momentum and heat. In the normal state, the sound diffusivity D monotonically decreases upon lowering the temperature, in contrast to the diverging behavior of weakly interacting Fermi liquids. Below the superfluid transition temperature, D attains a universal value set by the ratio of Planck's constant and the particle mass. Our findings inform theories of fermion transport, with relevance for hydrodynamic flow of electrons, neutrons, and quarks.
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Affiliation(s)
- Parth B Patel
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Zhenjie Yan
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Biswaroop Mukherjee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Richard J Fletcher
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Julian Struck
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Département de Physique, Ecole Normale Supérieure/PSL Research University, CNRS, 24 rue Lhomond, 75005 Paris, France
| | - Martin W Zwierlein
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. .,MIT-Harvard Center for Ultracold Atoms, Cambridge, MA 02139, USA.,Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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14
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Kwon WJ, Del Pace G, Panza R, Inguscio M, Zwerger W, Zaccanti M, Scazza F, Roati G. Strongly correlated superfluid order parameters from dc Josephson supercurrents. Science 2020; 369:84-88. [DOI: 10.1126/science.aaz2463] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Accepted: 04/27/2020] [Indexed: 11/02/2022]
Affiliation(s)
- W. J. Kwon
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - G. Del Pace
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Department of Physics and Astronomy, University of Florence, 50019 Sesto Fiorentino, Italy
| | - R. Panza
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - M. Inguscio
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Department of Engineering, Campus Bio-Medico University of Rome, 00128 Rome, Italy
| | - W. Zwerger
- Physics Department, Technische Universität München, 85747 Garching, Germany
| | - M. Zaccanti
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - F. Scazza
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - G. Roati
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
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15
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Bohlen M, Sobirey L, Luick N, Biss H, Enss T, Lompe T, Moritz H. Sound Propagation and Quantum-Limited Damping in a Two-Dimensional Fermi Gas. PHYSICAL REVIEW LETTERS 2020; 124:240403. [PMID: 32639806 DOI: 10.1103/physrevlett.124.240403] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 04/26/2020] [Accepted: 05/22/2020] [Indexed: 06/11/2023]
Abstract
Strongly interacting two-dimensional Fermi systems are one of the great remaining challenges in many-body physics due to the interplay of strong local correlations and enhanced long-range fluctuations. Here, we probe the thermodynamic and transport properties of a 2D Fermi gas across the BEC-BCS crossover by studying the propagation and damping of sound modes. We excite particle currents by imprinting a phase step onto homogeneous Fermi gases trapped in a box potential and extract the speed of sound from the frequency of the resulting density oscillations. We measure the speed of sound across the BEC-BCS crossover and compare the resulting dynamic measurement of the equation of state both to a static measurement based on recording density profiles and to quantum Monte Carlo calculations and find reasonable agreement between all three. We also measure the damping of the sound mode, which is determined by the shear and bulk viscosities as well as the thermal conductivity of the gas. We find that the damping is minimal in the strongly interacting regime and the diffusivity approaches the universal quantum bound ℏ/m of a perfect fluid.
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Affiliation(s)
- Markus Bohlen
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
- Laboratoire Kastler Brossel, ENS-Université PSL, CNRS, Sorbonne Université, Collège de France, 24 rue Lhomond, Paris 75005, France
| | - Lennart Sobirey
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
| | - Niclas Luick
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
| | - Hauke Biss
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
| | - Tilman Enss
- Intitut für Theoretische Physik, Universität Heidelberg, Philosophenweg 19, Heidelberg 69120, Germany
| | - Thomas Lompe
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
| | - Henning Moritz
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, Hamburg 22761, Germany
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16
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Kuhn CCN, Hoinka S, Herrera I, Dyke P, Kinnunen JJ, Bruun GM, Vale CJ. High-Frequency Sound in a Unitary Fermi Gas. PHYSICAL REVIEW LETTERS 2020; 124:150401. [PMID: 32357063 DOI: 10.1103/physrevlett.124.150401] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Accepted: 02/25/2020] [Indexed: 06/11/2023]
Abstract
We present an experimental and theoretical study of the phonon mode in a unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation spectra at a momentum of approximately half the Fermi momentum, both above and below the superfluid critical temperature T_{c}. Below T_{c}, the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by gradients in the phase of the superfluid order parameter. The temperature dependence of the BA phonon is consistent with a theoretical model based on the quasiparticle random phase approximation in which the dominant damping mechanism is via collisions with thermally excited quasiparticles. As the temperature is increased above T_{c}, the phonon evolves into a strongly damped collisional mode, accompanied by an abrupt increase in spectral width. Our study reveals strong similarities between sound propagation in the unitary Fermi gas and bosonic liquid helium.
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Affiliation(s)
- C C N Kuhn
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia
| | - S Hoinka
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia
| | - I Herrera
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia
| | - P Dyke
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia
| | - J J Kinnunen
- Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
| | - G M Bruun
- Institut for Fysik og Astronomi, Aarhus Universitet, 8000 Aarhus C, Denmark
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
| | - C J Vale
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia
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17
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Van Loon S, Tempere J, Kurkjian H. Beyond Mean-Field Corrections to the Quasiparticle Spectrum of Superfluid Fermi Gases. PHYSICAL REVIEW LETTERS 2020; 124:073404. [PMID: 32142351 DOI: 10.1103/physrevlett.124.073404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 12/02/2019] [Accepted: 01/21/2020] [Indexed: 06/10/2023]
Abstract
We investigate the fermionic quasiparticle branch of superfluid Fermi gases in the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) crossover and calculate the quasiparticle lifetime and energy shift due to its coupling with the collective mode. The only close-to-resonance process that low-energy quasiparticles can undergo at zero temperature is the emission of a bosonic excitation from the phononic branch. Close to the minimum of the branch we find that the quasiparticles remain undamped, allowing us to compute corrections to experimentally relevant quantities such as the energy gap, location of the minimum, effective mass, and Landau critical velocity.
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Affiliation(s)
- Senne Van Loon
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, België
| | - Jacques Tempere
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, België
| | - Hadrien Kurkjian
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, België
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18
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The low-energy Goldstone mode in a trapped dipolar supersolid. Nature 2019; 574:386-389. [DOI: 10.1038/s41586-019-1569-5] [Citation(s) in RCA: 91] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 08/29/2019] [Indexed: 11/08/2022]
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19
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Aubry GJ, Roux P. Topological Effects of a Vorticity Filament on the Coherent Backscattering Cone. PHYSICAL REVIEW LETTERS 2019; 123:035503. [PMID: 31386480 DOI: 10.1103/physrevlett.123.035503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Indexed: 06/10/2023]
Abstract
In this Letter, we report on the effects of a vorticity filament on the coherent backscattering cone. Using ultrasonic waves in a strongly reverberating cavity, we experimentally show that the discrete number of loops of acoustic paths around a pointlike vortex located at the center of the cavity drives the cancellation and the potential rebirth of the coherent backscattering enhancement. The vorticity filament behaves, then, as a topological anomaly for wave propagation that provides some new insight between reciprocity and weak localization.
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Affiliation(s)
- Geoffroy J Aubry
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - Philippe Roux
- Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France
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20
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Tiberkevich V, Borisenko IV, Nowik-Boltyk P, Demidov VE, Rinkevich AB, Demokritov SO, Slavin AN. Excitation of coherent second sound waves in a dense magnon gas. Sci Rep 2019; 9:9063. [PMID: 31227729 PMCID: PMC6588561 DOI: 10.1038/s41598-019-44956-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Accepted: 05/23/2019] [Indexed: 11/08/2022] Open
Abstract
Second sound is a quantum mechanical effect manifesting itself as a wave-like (in contrast with diffusion) heat transfer, or energy propagation, in a gas of quasi-particles. So far, this phenomenon has been observed only in an equilibrium gas of phonons existing in liquid/solid helium, or in dielectric crystals (Bi, NaF) at low temperatures. Here, we report observation of a room-temperature magnonic second sound, or a wave-like transport of both energy and spin angular momentum, in a quasi-equilibrium gas of magnons undergoing Bose-Einstein condensation (BEC) in a ferrite film. Due to the contact of the magnon gas with pumping photons and phonons, dispersion of the magnonic second sound differ qualitatively from the phononic case, as there is no diffusion regime, and the second sound velocity remains finite at low wavenumbers. Formation of BEC in the gas of magnons modifies the second sound properties by creating an additional channel of energy relaxation.
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Affiliation(s)
- V Tiberkevich
- Department of Physics, OaklandUniversity, Rochester, MI, USA.
| | - I V Borisenko
- Departmentof Physics and Center for Nonlinear Science, University of Muenster, Corrensstrasse 2-4, 48149, Muenster, Germany
- Kotel'nikov Institute of Radio Engineering and Electronics, RussianAcademy of Sciences, 125009, Moscow, Russia
| | - P Nowik-Boltyk
- Departmentof Physics and Center for Nonlinear Science, University of Muenster, Corrensstrasse 2-4, 48149, Muenster, Germany
| | - V E Demidov
- Departmentof Physics and Center for Nonlinear Science, University of Muenster, Corrensstrasse 2-4, 48149, Muenster, Germany
| | - A B Rinkevich
- Institute of Metal Physics, Ural Division of RAS, Ekaterinburg, 620041, Russia
| | - S O Demokritov
- Departmentof Physics and Center for Nonlinear Science, University of Muenster, Corrensstrasse 2-4, 48149, Muenster, Germany
- Institute of Metal Physics, Ural Division of RAS, Ekaterinburg, 620041, Russia
| | - A N Slavin
- Department of Physics, OaklandUniversity, Rochester, MI, USA
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21
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Hirsbrunner MR, Philip TM, Basa B, Kim Y, Jip Park M, Gilbert MJ. A review of modeling interacting transient phenomena with non-equilibrium Green functions. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2019; 82:046001. [PMID: 30641508 DOI: 10.1088/1361-6633/aafe5f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
As experimental probes have matured to observe ultrafast transient and high frequency responses of materials and devices, so to have the theoretical methods to numerically and analytically simulate time- and frequency-resolved transport. In this review article, we discuss recent progress in the development of the time-dependent and frequency-dependent non-equilibrium Green function (NEGF) technique. We begin with an overview of the theoretical underpinnings of the underlying Kadanoff-Baym equations and derive the fundamental NEGF equations in the time and frequency domains. We discuss how these methods have been applied to a variety of condensed matter systems such as molecular electronics, nanoscale transistors, and superconductors. In addition, we survey the application of NEGF in fields beyond condensed matter, where it has been used to study thermalization in ultra-cold atoms and to understand leptogenesis in the early universe. Throughout, we pay special attention to the challenges of incorporating contacts and interactions, as the NEGF method is uniquely capable of accounting for such features.
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Affiliation(s)
- Mark R Hirsbrunner
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States of America
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22
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Ota M, Larcher F, Dalfovo F, Pitaevskii L, Proukakis NP, Stringari S. Collisionless Sound in a Uniform Two-Dimensional Bose Gas. PHYSICAL REVIEW LETTERS 2018; 121:145302. [PMID: 30339431 DOI: 10.1103/physrevlett.121.145302] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Indexed: 06/08/2023]
Abstract
Using linear response theory within the random phase approximation, we investigate the propagation of sound in a uniform two dimensional (2D) Bose gas in the collisionless regime. We show that the sudden removal of a static density perturbation produces a damped oscillatory behavior revealing that sound can propagate also in the absence of collisions, due to mean-field interaction effects. We provide explicit results for the sound velocity and damping as a function of temperature, pointing out the crucial role played by Landau damping. We support our predictions by performing numerical simulations with the stochastic (projected) Gross-Pitaevskii equation. The results are consistent with the recent experimental observation of sound in a weakly interacting 2D Bose gas both below and above the superfluid Berezinskii-Kosterlitz-Thouless transition.
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Affiliation(s)
- Miki Ota
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento, Italy
| | - Fabrizio Larcher
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento, Italy
- Joint Quantum Centre Durham-Newcastle, School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom
| | - Franco Dalfovo
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento, Italy
| | - Lev Pitaevskii
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento, Italy
- Kapitza Institute for Physical Problems, Russian Academy of Science, Kosygina 2, 119334 Moscow, Russia
| | - Nick P Proukakis
- Joint Quantum Centre Durham-Newcastle, School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom
| | - Sandro Stringari
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento, Italy
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23
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Ville JL, Saint-Jalm R, Le Cerf É, Aidelsburger M, Nascimbène S, Dalibard J, Beugnon J. Sound Propagation in a Uniform Superfluid Two-Dimensional Bose Gas. PHYSICAL REVIEW LETTERS 2018; 121:145301. [PMID: 30339451 DOI: 10.1103/physrevlett.121.145301] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Indexed: 06/08/2023]
Abstract
In superfluid systems several sound modes can be excited, such as, for example, first and second sound in liquid helium. Here, we excite running and standing waves in a uniform two-dimensional Bose gas and we characterize the propagation of sound in both the superfluid and normal regimes. In the superfluid phase, the measured speed of sound is in good agreement with the prediction of a two-fluid hydrodynamic model, and the weak damping is well explained by the scattering with thermal excitations. In the normal phase we observe a stronger damping, which we attribute to a departure from hydrodynamic behavior.
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Affiliation(s)
- J L Ville
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - R Saint-Jalm
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - É Le Cerf
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - M Aidelsburger
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - S Nascimbène
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - J Dalibard
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
| | - J Beugnon
- Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université, 11 Place Marcelin Berthelot, 75005 Paris, France
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24
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Gänger B, Phieler J, Nagler B, Widera A. A versatile apparatus for fermionic lithium quantum gases based on an interference-filter laser system. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:093105. [PMID: 30278689 DOI: 10.1063/1.5045827] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Accepted: 08/25/2018] [Indexed: 06/08/2023]
Abstract
We report on the design and construction of a versatile setup for experiments with ultracold lithium (Li) gases. We discuss our methods to prepare an atomic beam and laser cool it in a Zeeman slower and a subsequent magneto-optical trap, which rely on established methods. We focus on our laser system based on a stable interference-filter-stabilized, linear-extended-cavity diode laser, so far unreported for lithium wavelengths. Moreover, we describe our optical setup to combine various laser frequencies for cooling, manipulation, and detection of Li atoms. We characterize the performance of our system preparing degenerate samples of Li atoms via forced evaporation in a hybrid crossed-beam optical-dipole trap plus confining magnetic trap. Our apparatus allows one to produce quantum gases of N ≈ 105…106 fermionic lithium-6 atoms at nanokelvin temperatures in cycle times below 10 s. Our optical system is particularly suited to study the dynamics of fermionic superfluids in engineered optical potentials.
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Affiliation(s)
- Benjamin Gänger
- Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Jan Phieler
- Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Benjamin Nagler
- Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Artur Widera
- Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
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25
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Abstract
We report on coupled heat and particle transport measurements through a quantum point contact (QPC) connecting two reservoirs of resonantly interacting, finite temperature Fermi gases. After heating one of them, we observe a particle current flowing from cold to hot. We monitor the temperature evolution of the reservoirs and find that the system evolves after an initial response into a nonequilibrium steady state with finite temperature and chemical potential differences across the QPC. In this state any relaxation in the form of heat and particle currents vanishes. From our measurements we extract the transport coefficients of the QPC and deduce a Lorenz number violating the Wiedemann-Franz law by one order of magnitude, a characteristic persisting even for a wide contact. In contrast, the Seebeck coefficient takes a value close to that expected for a noninteracting Fermi gas and shows a smooth decrease as the atom density close to the QPC is increased beyond the superfluid transition. Our work represents a fermionic analog of the fountain effect observed with superfluid helium and poses challenges for microscopic modeling of the finite temperature dynamics of the unitary Fermi gas.
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26
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Matveev KA, Andreev AV. Hybrid Sound Modes in One-Dimensional Quantum Liquids. PHYSICAL REVIEW LETTERS 2018; 121:026803. [PMID: 30085735 DOI: 10.1103/physrevlett.121.026803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Indexed: 06/08/2023]
Abstract
We study sound in a single-channel one-dimensional quantum liquid. In contrast to classical fluids, instead of a single sound mode we find two modes of density oscillations. The speeds at which these two sound modes propagate are nearly equal, with the difference that scales linearly with the small temperature of the system. The two sound modes emerge as hybrids of the first and second sounds, and combine oscillations of both density and entropy of the liquid.
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Affiliation(s)
- K A Matveev
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - A V Andreev
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
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27
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Fava E, Bienaimé T, Mordini C, Colzi G, Qu C, Stringari S, Lamporesi G, Ferrari G. Observation of Spin Superfluidity in a Bose Gas Mixture. PHYSICAL REVIEW LETTERS 2018; 120:170401. [PMID: 29756820 DOI: 10.1103/physrevlett.120.170401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Indexed: 06/08/2023]
Abstract
The spin dynamics of a harmonically trapped Bose-Einstein condensed binary mixture of sodium atoms is experimentally investigated at finite temperature. In the collisional regime the motion of the thermal component is shown to be damped because of spin drag, while the two condensates exhibit a counterflow oscillation without friction, thereby providing direct evidence for spin superfluidity. Results are also reported in the collisionless regime where the spin components of both the condensate and thermal part oscillate without damping, their relative motion being driven by a mean-field effect. We also measure the static polarizability of the condensed and thermal parts and we find a large increase of the condensate polarizability with respect to the T=0 value, in agreement with the predictions of theory.
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Affiliation(s)
- Eleonora Fava
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
| | - Tom Bienaimé
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
| | - Carmelo Mordini
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
- Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy
| | - Giacomo Colzi
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
- Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy
| | - Chunlei Qu
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
| | - Sandro Stringari
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
- Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy
| | - Giacomo Lamporesi
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
- Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy
| | - Gabriele Ferrari
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
- Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy
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28
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Matveev KA, Andreev AV. Second Sound in Systems of One-Dimensional Fermions. PHYSICAL REVIEW LETTERS 2017; 119:266801. [PMID: 29328707 DOI: 10.1103/physrevlett.119.266801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Indexed: 06/07/2023]
Abstract
We study sound in Galilean invariant systems of one-dimensional fermions. At low temperatures, we find a broad range of frequencies in which in addition to the waves of density there is a second sound corresponding to the ballistic propagation of heat in the system. The damping of the second sound mode is weak, provided the frequency is large compared to a relaxation rate that is exponentially small at low temperatures. At lower frequencies, the second sound mode is damped, and the propagation of heat is diffusive.
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Affiliation(s)
- K A Matveev
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - A V Andreev
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
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29
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Cinti F, Cappellaro A, Salasnich L, Macrì T. Superfluid Filaments of Dipolar Bosons in Free Space. PHYSICAL REVIEW LETTERS 2017; 119:215302. [PMID: 29219392 DOI: 10.1103/physrevlett.119.215302] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Indexed: 06/07/2023]
Abstract
We systematically investigate the zero temperature phase diagram of bosons interacting via dipolar interactions in three dimensions in free space via path integral Monte Carlo simulations with a few hundreds of particles and periodic boundary conditions based on the worm algorithm. Upon increasing the strength of the dipolar interaction and at sufficiently high densities we find a wide region where filaments are stabilized along the direction of the external field. Most interestingly by computing the superfluid fraction we conclude that the superfluidity is anisotropic and is greatly suppressed along the orthogonal plane. Finally, we perform simulations at finite temperature confirming the stability of the filaments against thermal fluctuations and provide an estimate of the superfluid fraction in the weak coupling limit in the framework of the Landau two-fluid model.
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Affiliation(s)
- Fabio Cinti
- National Institute for Theoretical Physics (NITheP), Stellenbosch 7600, South Africa
- Institute of Theoretical Physics, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Alberto Cappellaro
- Dipartimento di Fisica e Astronomia Galileo Galilei and CNISM, Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Luca Salasnich
- Dipartimento di Fisica e Astronomia Galileo Galilei and CNISM, Università di Padova, via Marzolo 8, 35131 Padova, Italy
- CNR-INO, via Nello Carrara, 1-50019 Sesto Fiorentino, Italy
| | - Tommaso Macrì
- Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, and International Institute of Physics, 59078-970 Natal, Rio Grande do Norte, Brazil
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30
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Krinner S, Esslinger T, Brantut JP. Two-terminal transport measurements with cold atoms. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:343003. [PMID: 28749788 DOI: 10.1088/1361-648x/aa74a1] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In recent years, the ability of cold atom experiments to explore condensed-matter-related questions has dramatically progressed. Transport experiments, in particular, have expanded to the point in which conductance and other transport coefficients can now be measured in a way that is directly analogous to solid-state physics, extending cold-atom-based quantum simulations into the domain of quantum electronic devices. In this topical review, we describe the transport experiments performed with cold gases in the two-terminal configuration, with an emphasis on the specific features of cold atomic gases compared to solid-state physics. We present the experimental techniques and the main experimental findings, focusing on-but not restricted to-the recent experiments performed by our group. We finally discuss the perspectives opened up by this approach, the main technical and conceptual challenges for future developments, and potential applications in quantum simulation for transport phenomena and mesoscopic physics problems.
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Affiliation(s)
- Sebastian Krinner
- Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland
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31
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Deng S, Shi ZY, Diao P, Yu Q, Zhai H, Qi R, Wu H. Observation of the Efimovian expansion in scale-invariant Fermi gases. Science 2016; 353:371-4. [DOI: 10.1126/science.aaf0666] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2015] [Accepted: 06/21/2016] [Indexed: 11/02/2022]
Affiliation(s)
- Shujin Deng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China
| | - Zhe-Yu Shi
- Institute for Advanced Study, Tsinghua University, Beijing 100084, P. R. China
| | - Pengpeng Diao
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China
| | - Qianli Yu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China
| | - Hui Zhai
- Institute for Advanced Study, Tsinghua University, Beijing 100084, P. R. China
| | - Ran Qi
- Department of Physics, Renmin University of China, Beijing 100872, P. R. China
| | - Haibin Wu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
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32
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Delehaye M, Laurent S, Ferrier-Barbut I, Jin S, Chevy F, Salomon C. Critical Velocity and Dissipation of an Ultracold Bose-Fermi Counterflow. PHYSICAL REVIEW LETTERS 2015; 115:265303. [PMID: 26765001 DOI: 10.1103/physrevlett.115.265303] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2015] [Indexed: 06/05/2023]
Abstract
We study the dynamics of counterflowing bosonic and fermionic lithium atoms. First, by tuning the interaction strength we measure the critical velocity v(c) of the system in the BEC-BCS crossover in the low temperature regime and we compare it to the recent prediction of Castin et al., C. R. Phys. 16, 241 (2015). Second, raising the temperature of the mixture slightly above the superfluid transitions reveals an unexpected phase locking of the oscillations of the clouds induced by dissipation.
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Affiliation(s)
- Marion Delehaye
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
| | - Sébastien Laurent
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
| | - Igor Ferrier-Barbut
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
| | - Shuwei Jin
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
| | - Frédéric Chevy
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
| | - Christophe Salomon
- Laboratoire Kastler Brossel, ENS-PSL, CNRS, UPMC-Sorbonne Universités, and Collège de France, 75005 Paris, France
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33
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Valtolina G, Burchianti A, Amico A, Neri E, Xhani K, Seman JA, Trombettoni A, Smerzi A, Zaccanti M, Inguscio M, Roati G. Josephson effect in fermionic superfluids across the BEC-BCS crossover. Science 2015; 350:1505-8. [DOI: 10.1126/science.aac9725] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 11/13/2015] [Indexed: 11/02/2022]
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34
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Superfluidity in topologically nontrivial flat bands. Nat Commun 2015; 6:8944. [PMID: 26586543 PMCID: PMC4673883 DOI: 10.1038/ncomms9944] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 10/19/2015] [Indexed: 11/08/2022] Open
Abstract
Topological invariants built from the periodic Bloch functions characterize new phases of matter, such as topological insulators and topological superconductors. The most important topological invariant is the Chern number that explains the quantized conductance of the quantum Hall effect. Here we provide a general result for the superfluid weight Ds of a multiband superconductor that is applicable to topologically nontrivial bands with nonzero Chern number C. We find that the integral over the Brillouin-zone of the quantum metric, an invariant calculated from the Bloch functions, gives the superfluid weight in a flat band, with the bound Ds⩾|C|. Thus, even a flat band can carry finite superfluid current, provided the Chern number is nonzero. As an example, we provide Ds for the time-reversal invariant attractive Harper-Hubbard model that can be experimentally tested in ultracold gases. In general, our results establish that a topologically nontrivial flat band is a promising concept for increasing the critical temperature of the superconducting transition.
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35
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Hou YH, Yu Z. Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling. Sci Rep 2015; 5:15307. [PMID: 26483090 PMCID: PMC4611183 DOI: 10.1038/srep15307] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 09/14/2015] [Indexed: 11/09/2022] Open
Abstract
Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.
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Affiliation(s)
- Yan-Hua Hou
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - Zhenhua Yu
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
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36
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Weimer W, Morgener K, Singh VP, Siegl J, Hueck K, Luick N, Mathey L, Moritz H. Critical velocity in the BEC-BCS crossover. PHYSICAL REVIEW LETTERS 2015; 114:095301. [PMID: 25793823 DOI: 10.1103/physrevlett.114.095301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Indexed: 06/04/2023]
Abstract
We map out the critical velocity in the crossover from Bose-Einstein condensation to Bardeen-Cooper-Schrieffer superfluidity with ultracold ^{6}Li gases. A small attractive potential is dragged along lines of constant column density. The rate of the induced heating increases steeply above a critical velocity v_{c}. In the same samples, we measure the speed of sound v_{s} by exciting density waves and compare the results to the measured values of v_{c}. We perform numerical simulations in the Bose-Einstein condensation regime and find very good agreement, validating the approach. In the strongly correlated regime our measurements of v_{c} provide a testing ground for theoretical approaches.
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Affiliation(s)
- Wolf Weimer
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Kai Morgener
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Vijay Pal Singh
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Jonas Siegl
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Klaus Hueck
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Niclas Luick
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Ludwig Mathey
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Henning Moritz
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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37
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Grenier C, Georges A, Kollath C. Peltier cooling of fermionic quantum gases. PHYSICAL REVIEW LETTERS 2014; 113:200601. [PMID: 25432033 DOI: 10.1103/physrevlett.113.200601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Indexed: 06/04/2023]
Abstract
We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling.
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Affiliation(s)
- Ch Grenier
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - A Georges
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France; Centre de Physique Théorique, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex, France; and DPMC, Université de Genève, CH-1211 Geneva, Switzerland
| | - C Kollath
- HISKP, University of Bonn, Nussallee 14-16, D-53115 Bonn, Germany
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38
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Papoular DJ, Pitaevskii LP, Stringari S. Fast thermalization and Helmholtz oscillations of an ultracold Bose gas. PHYSICAL REVIEW LETTERS 2014; 113:170601. [PMID: 25379907 DOI: 10.1103/physrevlett.113.170601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Indexed: 06/04/2023]
Abstract
We analyze theoretically the transport properties of a weakly interacting ultracold Bose gas enclosed in two reservoirs connected by a constriction. We assume that the transport of the superfluid part is hydrodynamic, and we describe the ballistic transport of the normal part using the Landauer-Büttiker formalism. Modeling the coupled evolution of the phase, atom number, and temperature mismatches between the reservoirs, we predict that Helmholtz (plasma) oscillations can be observed at nonzero temperatures below Tc. We show that, because of its strong compressibility, the Bose gas is characterized by a fast thermalization compared to the damping time for plasma oscillations, accompanied by a fast transfer of the normal component. This fast thermalization also affects the gas above Tc, where we present a comparison to the ideal fermionic case. Moreover, we outline the possible realization of a superleak through the inclusion of a disordered potential.
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Affiliation(s)
- D J Papoular
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
| | - L P Pitaevskii
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy and Kapitza Institute for Physical Problems, Kosygina 2, 119334 Moscow, Russia
| | - S Stringari
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy
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39
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Matsunaga R, Tsuji N, Fujita H, Sugioka A, Makise K, Uzawa Y, Terai H, Wang Z, Aoki H, Shimano R. Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor. Science 2014; 345:1145-9. [PMID: 25011555 DOI: 10.1126/science.1254697] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Superconductors host collective modes that can be manipulated with light. We show that a strong terahertz light field can induce oscillations of the superconducting order parameter in NbN with twice the frequency of the terahertz field. The result can be captured as a collective precession of Anderson's pseudospins in ac driving fields. A resonance between the field and the Higgs amplitude mode of the superconductor then results in large terahertz third-harmonic generation. The method we present here paves a way toward nonlinear quantum optics in superconductors with driving the pseudospins collectively and can be potentially extended to exotic superconductors for shedding light on the character of order parameters and their coupling to other degrees of freedom.
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Affiliation(s)
- Ryusuke Matsunaga
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan.
| | - Naoto Tsuji
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan
| | - Hiroyuki Fujita
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan
| | - Arata Sugioka
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan
| | - Kazumasa Makise
- Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan
| | - Yoshinori Uzawa
- National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
| | - Hirotaka Terai
- Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan
| | - Zhen Wang
- Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan
| | - Hideo Aoki
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
| | - Ryo Shimano
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. Cryogenic Research Center, University of Tokyo, Yayoi, Tokyo 113-0032, Japan.
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40
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Bardon AB, Beattie S, Luciuk C, Cairncross W, Fine D, Cheng NS, Edge GJA, Taylor E, Zhang S, Trotzky S, Thywissen JH. Transverse Demagnetization Dynamics of a Unitary Fermi Gas. Science 2014; 344:722-4. [DOI: 10.1126/science.1247425] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- A. B. Bardon
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - S. Beattie
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - C. Luciuk
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - W. Cairncross
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - D. Fine
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - N. S. Cheng
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - G. J. A. Edge
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - E. Taylor
- Department of Physics and Astronomy, McMaster University, L8S 4M1 Canada
| | - S. Zhang
- Department of Physics, Center of Theoretical and Computational Physics, University of Hong Kong, China
| | - S. Trotzky
- Department of Physics, University of Toronto, M5S 1A7 Canada
| | - J. H. Thywissen
- Department of Physics, University of Toronto, M5S 1A7 Canada
- Canadian Institute for Advanced Research, Toronto, Ontario, M5G 1Z8 Canada
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41
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Gusakov ME, Chugunov AI, Kantor EM. Instability windows and evolution of rapidly rotating neutron stars. PHYSICAL REVIEW LETTERS 2014; 112:151101. [PMID: 24785021 DOI: 10.1103/physrevlett.112.151101] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Indexed: 05/27/2023]
Abstract
We consider an instability of rapidly rotating neutron stars in low-mass x-ray binaries (LMXBs) with respect to excitation of r modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. Using a simple phenomenological model we demonstrate that neutron stars with high spin frequency may spend a substantial amount of time at these "resonance" temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot, nonaccreting, rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB candidates. We also impose a new theoretical limit on the neutron star spin frequency, which can explain the cutoff spin frequency ∼730 Hz, following from the statistical analysis of accreting millisecond x-ray pulsars. In addition to explaining the observations, our model provides a new tool to constrain superdense matter properties by comparing measured and theoretically predicted resonance temperatures.
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Affiliation(s)
- Mikhail E Gusakov
- Ioffe Institute, Polytekhnicheskaya 26, 194021 St.-Petersburg, Russia and St.-Petersburg State Polytechnical University, Polytekhnicheskaya 29, 195251 St.-Petersburg, Russia
| | - Andrey I Chugunov
- Ioffe Institute, Polytekhnicheskaya 26, 194021 St.-Petersburg, Russia
| | - Elena M Kantor
- Ioffe Institute, Polytekhnicheskaya 26, 194021 St.-Petersburg, Russia
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42
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Alford MG, Mallavarapu SK, Schmitt A, Stetina S. Role reversal in first and second sound in a relativistic superfluid. Int J Clin Exp Med 2014. [DOI: 10.1103/physrevd.89.085005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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43
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44
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Lingham MG, Fenech K, Hoinka S, Vale CJ. Local observation of pair condensation in a Fermi gas at unitarity. PHYSICAL REVIEW LETTERS 2014; 112:100404. [PMID: 24679273 DOI: 10.1103/physrevlett.112.100404] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Indexed: 06/03/2023]
Abstract
We present measurements of the local (homogeneous) density-density response function of a Fermi gas at unitarity using spatially resolved Bragg spectroscopy. By analyzing the Bragg response across one axis of the cloud, we extract the response function for a uniform gas which shows a clear signature of the Bose-Einstein condensation of pairs of fermions when the local temperature drops below the superfluid transition temperature. The method we use for local measurement generalizes a scheme for obtaining the local pressure in a harmonically trapped cloud from the line density and can be adapted to provide any homogeneous parameter satisfying the local density approximation.
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Affiliation(s)
- M G Lingham
- Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
| | - K Fenech
- Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
| | - S Hoinka
- Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
| | - C J Vale
- Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
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45
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Ozawa T, Stringari S. Discontinuities in the first and second sound velocities at the Berezinskii-Kosterlitz-Thouless transition. PHYSICAL REVIEW LETTERS 2014; 112:025302. [PMID: 24484023 DOI: 10.1103/physrevlett.112.025302] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Indexed: 06/03/2023]
Abstract
We calculate the temperature dependence of the first and second sound velocities in the superfluid phase of a 2D dilute Bose gas by solving Landau's two fluid hydrodynamic equations. We predict the occurrence of a significant discontinuity in both velocities at the critical temperature, as a consequence of the jump of the superfluid density characterizing the Berezinskii-Kosterlitz-Thouless transition. The key role of the thermal expansion coefficient is discussed. We find that second sound in this dilute Bose gas can be easily excited through a density perturbation, thereby, making the perspective of the measurement of the superfluid density particularly favorable.
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Affiliation(s)
- Tomoki Ozawa
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, I-38123 Povo, Italy
| | - Sandro Stringari
- INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, I-38123 Povo, Italy
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46
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Bulgac A, Forbes MM, Kelley MM, Roche KJ, Wlazłowski G. Quantized superfluid vortex rings in the unitary Fermi gas. PHYSICAL REVIEW LETTERS 2014; 112:025301. [PMID: 24484022 DOI: 10.1103/physrevlett.112.025301] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Indexed: 06/03/2023]
Abstract
In a recent article, Yefsah et al. [Nature (London) 499, 426 (2013)] report the observation of an unusual excitation in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe oscillations almost an order of magnitude slower than predicted by any theory of domain walls which they interpret as a "heavy soliton" of inertial mass some 200 times larger than the free fermion mass or 50 times larger than expected for a domain wall. We present compelling evidence that this "soliton" is instead a quantized vortex ring, by showing that the main aspects of the experiment can be naturally explained within the framework of time-dependent superfluid density functional theories.
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Affiliation(s)
- Aurel Bulgac
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA
| | - Michael McNeil Forbes
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA and Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195-1550, USA and Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814, USA
| | - Michelle M Kelley
- Department of Physics, University of Illinois at Urbana-Champaign, Il 61801-3080, USA
| | - Kenneth J Roche
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA and Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Gabriel Wlazłowski
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA and Faculty of Physics, Warsaw University of Technology, Ulica Koszykowa 75, 00-662 Warsaw, Poland
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Krauser JS, Ebling U, Fläschner N, Heinze J, Sengstock K, Lewenstein M, Eckardt A, Becker C. Giant Spin Oscillations in an Ultracold Fermi Sea. Science 2014; 343:157-60. [DOI: 10.1126/science.1244059] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- J. S. Krauser
- ILP (Institut für Laserphysik), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - U. Ebling
- ICFO (Institut de Ciències Fotòniques), Avenida Carl Friedrich Gauss 3, 08860 Castelldefels, Spain
| | - N. Fläschner
- ILP (Institut für Laserphysik), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - J. Heinze
- ILP (Institut für Laserphysik), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - K. Sengstock
- ILP (Institut für Laserphysik), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- ZOQ (Zentrum für Optische Quantentechnologien), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - M. Lewenstein
- ICFO (Institut de Ciències Fotòniques), Avenida Carl Friedrich Gauss 3, 08860 Castelldefels, Spain
- ICREA (Institució Catalana de Recerca i Estudis Avançats), Lluís Companys 23, 08010 Barcelona, Spain
| | - A. Eckardt
- MPI-PKS (Max-Planck-Institut für Physik komplexer Systeme), Nöthnitzer Straße 38, 01187 Dresden, Germany
| | - C. Becker
- ILP (Institut für Laserphysik), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- ZOQ (Zentrum für Optische Quantentechnologien), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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Affiliation(s)
- Li You
- Department of Physics, Tsinghua University, China
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Brantut JP, Grenier C, Meineke J, Stadler D, Krinner S, Kollath C, Esslinger T, Georges A. A thermoelectric heat engine with ultracold atoms. Science 2013; 342:713-5. [PMID: 24158905 DOI: 10.1126/science.1242308] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Thermoelectric effects, such as the generation of a particle current by a temperature gradient, have their origin in a reversible coupling between heat and particle flows. These effects are fundamental probes for materials and have applications to cooling and power generation. Here, we demonstrate thermoelectricity in a fermionic cold atoms channel in the ballistic and diffusive regimes, connected to two reservoirs. We show that the magnitude of the effect and the efficiency of energy conversion can be optimized by controlling the geometry or disorder strength. Our observations are in quantitative agreement with a theoretical model based on the Landauer-Büttiker formalism. Our device provides a controllable model system to explore mechanisms of energy conversion and realizes a cold atom-based heat engine.
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