1
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Li X, Wang S, Luo X, Zhou YY, Xie K, Shen HC, Nie YZ, Chen Q, Hu H, Chen YA, Yao XC, Pan JW. Observation and quantification of the pseudogap in unitary Fermi gases. Nature 2024; 626:288-293. [PMID: 38326594 DOI: 10.1038/s41586-023-06964-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Accepted: 12/12/2023] [Indexed: 02/09/2024]
Abstract
The microscopic origin of high-temperature superconductivity in cuprates remains unknown. It is widely believed that substantial progress could be achieved by better understanding of the pseudogap phase, a normal non-superconducting state of cuprates1,2. In particular, a central issue is whether the pseudogap could originate from strong pairing fluctuations3. Unitary Fermi gases4,5, in which the pseudogap-if it exists-necessarily arises from many-body pairing, offer ideal quantum simulators to address this question. Here we report the observation of a pair-fluctuation-driven pseudogap in homogeneous unitary Fermi gases of lithium-6 atoms, by precisely measuring the fermion spectral function through momentum-resolved microwave spectroscopy and without spurious effects from final-state interactions. The temperature dependence of the pairing gap, inverse pair lifetime and single-particle scattering rate are quantitatively determined by analysing the spectra. We find a large pseudogap above the superfluid transition temperature. The inverse pair lifetime exhibits a thermally activated exponential behaviour, uncovering the microscopic virtual pair breaking and recombination mechanism. The obtained large, temperature-independent single-particle scattering rate is comparable with that set by the Planckian limit6. Our findings quantitatively characterize the pseudogap in strongly interacting Fermi gases and they lend support for the role of preformed pairing as a precursor to superfluidity.
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Affiliation(s)
- Xi Li
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei, China
| | - Shuai Wang
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Xiang Luo
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Yu-Yang Zhou
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Ke Xie
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Hong-Chi Shen
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Yu-Zhao Nie
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
| | - Qijin Chen
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei, China
| | - Hui Hu
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China
- Centre for Quantum Technology Theory, Swinburne University of Technology, Melbourne, Victoria, Australia
| | - Yu-Ao Chen
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China.
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China.
- Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
| | - Xing-Can Yao
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China.
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China.
- Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
| | - Jian-Wei Pan
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China.
- Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China.
- Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
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2
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Harrison N, Chan MK. Harrison and Chan Reply. PHYSICAL REVIEW LETTERS 2023; 130:199702. [PMID: 37243646 DOI: 10.1103/physrevlett.130.199702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 04/06/2023] [Indexed: 05/29/2023]
Affiliation(s)
- N Harrison
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - M K Chan
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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3
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Morita Y, Yoshioka K, Kuwata-Gonokami M. Observation of Bose-Einstein condensates of excitons in a bulk semiconductor. Nat Commun 2022; 13:5388. [PMID: 36104375 PMCID: PMC9474864 DOI: 10.1038/s41467-022-33103-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Accepted: 08/31/2022] [Indexed: 11/25/2022] Open
Abstract
An unambiguous observation of the Bose-Einstein condensation (BEC) of excitons in a photoexcited bulk semiconductor and elucidation of its inherent nature have been longstanding problems in condensed matter physics. Here, we observe the quantum phase transition and a Bose-Einstein condensate appearing in a trapped gas of 1s paraexcitons in bulk Cu2O below 400 mK, by directly visualizing the exciton cloud in real space using mid-infrared induced absorption imaging that we realized in a dilution refrigerator. Our study shows that the paraexciton condensate is undetectable by conventional luminescence spectroscopy. We find an unconventionally small condensate fraction of 0.016 with the spatial profile of the condensate well described by mean-field theory. Our discovery of this new type of BEC in the purely matter-like exciton system interacting with a cold phonon bath could pave the way for the classification of its long-range order, and for essential understanding of quantum statistical mechanics of non-equilibrium open systems. Bose-Einstein condensate of excitons is expected in photo-excited bulk semiconductors, but a direct experimental evidence has been lacking. Here the authors report the observation of a condensate of 1s paraexcitons in Cu2O using real-space mid-infrared absorption imaging realized in a dilution refrigerator.
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4
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Su Z, Yang H, Cao J, Wang XY, Rui J, Zhao B, Pan JW. Resonant Control of Elastic Collisions between ^{23}Na^{40}K Molecules and ^{40}K Atoms. PHYSICAL REVIEW LETTERS 2022; 129:033401. [PMID: 35905340 DOI: 10.1103/physrevlett.129.033401] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 04/24/2022] [Accepted: 07/01/2022] [Indexed: 06/15/2023]
Abstract
We have demonstrated the resonant control of the elastic scattering cross sections in the vicinity of Feshbach resonances between ^{23}Na^{40}K molecules and ^{40}K atoms by studying the thermalization between them. The elastic scattering cross sections vary by more than 2 orders of magnitude close to the resonance, and can be well described by an asymmetric Fano profile. The parameters that characterize the magnetically tunable s-wave scattering length are determined from the elastic scattering cross sections. The observation of resonantly controlled elastic scattering cross sections opens up the possibility to study strongly interacting atom-molecule mixtures and improve our understanding of the complex atom-molecule Feshbach resonances.
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Affiliation(s)
- Zhen Su
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Huan Yang
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Jin Cao
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Xin-Yao Wang
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Jun Rui
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Bo Zhao
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Jian-Wei Pan
- Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China; Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China; and Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
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5
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Harrison N, Chan MK. Magic Gap Ratio for Optimally Robust Fermionic Condensation and Its Implications for High-T_{c} Superconductivity. PHYSICAL REVIEW LETTERS 2022; 129:017001. [PMID: 35841553 DOI: 10.1103/physrevlett.129.017001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 03/22/2022] [Accepted: 05/24/2022] [Indexed: 06/15/2023]
Abstract
Bardeen-Schrieffer-Cooper (BCS) and Bose-Einstein condensation (BEC) occur at opposite limits of a continuum of pairing interaction strength between fermions. A crossover between these limits is readily observed in a cold atomic Fermi gas. Whether it occurs in other systems such as the high temperature superconducting cuprates has remained an open question. We uncover here unambiguous evidence for a BCS-BEC crossover in the cuprates by identifying a universal magic gap ratio 2Δ/k_{B}T_{c}≈6.5 (where Δ is the pairing gap and T_{c} is the transition temperature) at which paired fermion condensates become optimally robust. At this gap ratio, corresponding to the unitary point in a cold atomic Fermi gas, the measured condensate fraction N_{0} and the height of the jump δγ(T_{c}) in the coefficient γ of the fermionic specific heat at T_{c} are strongly peaked. In the cuprates, δγ(T_{c}) is peaked at this gap ratio when Δ corresponds to the antinodal spectroscopic gap, thus reinforcing its interpretation as the pairing gap. We find the peak in δγ(T_{c}) also to coincide with a normal state maximum in γ, which is indicative of a pairing fluctuation pseudogap above T_{c}.
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Affiliation(s)
- N Harrison
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M K Chan
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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6
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Sheng X, Li M, Tang KT. An accurate potential model for the a 3Σ u+ state of the lithium dimer. Phys Chem Chem Phys 2022; 24:13325-13334. [PMID: 35608033 DOI: 10.1039/d2cp01490d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An accurate Tang-Toennies (TT) model potential is introduced to describe the interatomic potential of the lithium dimer in the a3Σu+ state. With only one well-known parameter, the ionization energy, the new model potential compares favorably with the experimentally fitted Morse/Long-range (MLR) potential of Dattani and Le Roy [J. Mol. Spectrosc., 2011, 268, 199] and is in excellent agreement with the state-of-the-art ab initio potential of Lesiuk et al. [Phys. Rev. A, 2020, 102, 062806]. With the known dispersion coefficients and the ionization energy, the new potential requires only two experimental parameters, namely the depth of the potential well De and its location Re. The new potential can be extended to the region of zero separation by the united atom limit.
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Affiliation(s)
- Xiaowei Sheng
- Anhui Province Key Laboratory of Optoelectric Materials Science and Technology, Department of Physics, Anhui Normal University, Anhui, Wuhu 241000, China
| | - Mengyuan Li
- Anhui Province Key Laboratory of Optoelectric Materials Science and Technology, Department of Physics, Anhui Normal University, Anhui, Wuhu 241000, China
| | - K T Tang
- Department of Physics, Pacific Lutheran University, Tacoma, Washington, 98447, USA.
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7
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Biss H, Sobirey L, Luick N, Bohlen M, Kinnunen JJ, Bruun GM, Lompe T, Moritz H. Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas. PHYSICAL REVIEW LETTERS 2022; 128:100401. [PMID: 35333076 DOI: 10.1103/physrevlett.128.100401] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Accepted: 01/25/2022] [Indexed: 06/14/2023]
Abstract
Ultracold atomic gases are a powerful tool to experimentally study strongly correlated quantum many-body systems. In particular, ultracold Fermi gases with tunable interactions have allowed to realize the famous BEC-BCS crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid of weakly bound Cooper pairs. However, large parts of the excitation spectrum of fermionic superfluids in the BEC-BCS crossover are still unexplored. In this work, we use Bragg spectroscopy to measure the full momentum-resolved low-energy excitation spectrum of strongly interacting ultracold Fermi gases. This enables us to directly observe the smooth transformation from a bosonic to a fermionic superfluid that takes place in the BEC-BCS crossover. We also use our spectra to determine the evolution of the superfluid gap and find excellent agreement with previous experiments and self-consistent T-matrix calculations both in the BEC and crossover regime. However, toward the BCS regime a calculation that includes the effects of particle-hole correlations shows better agreement with our data.
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Affiliation(s)
- Hauke Biss
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Lennart Sobirey
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Niclas Luick
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Markus Bohlen
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Jami J Kinnunen
- Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Georg M Bruun
- Center for Complex Quantum Systems, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
| | - Thomas Lompe
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Henning Moritz
- Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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8
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Dmitriev VV, Kutuzov MS, Soldatov AA, Yudin AN. Superfluid β phase of ^{3}He. PHYSICAL REVIEW LETTERS 2021; 127:265301. [PMID: 35029470 DOI: 10.1103/physrevlett.127.265301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2021] [Accepted: 11/05/2021] [Indexed: 06/14/2023]
Abstract
It is known that in low magnetic fields the superfluid transition of ^{3}He in nematic aerogel occurs into the polar phase. Using a vibrating aerogel resonator, we observe that in high magnetic fields this transition splits into two discrete transitions, occurring at different temperatures. According to theoretical models, a new superfluid phase-the β phase-should be realized between these two transitions. The temperature range of existence of the new phase is measured as a function of magnetic field. The results are well consistent with theoretical expectations for the β phase.
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Affiliation(s)
- V V Dmitriev
- P.L. Kapitza Institute for Physical Problems of RAS, 119334 Moscow, Russia
| | - M S Kutuzov
- Metallurg Engineering Ltd., 11415 Tallinn, Estonia
| | - A A Soldatov
- P.L. Kapitza Institute for Physical Problems of RAS, 119334 Moscow, Russia
| | - A N Yudin
- P.L. Kapitza Institute for Physical Problems of RAS, 119334 Moscow, Russia
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9
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Grémaud B, Batrouni GG. Pairing and Pair Superfluid Density in One-Dimensional Two-Species Fermionic and Bosonic Hubbard Models. PHYSICAL REVIEW LETTERS 2021; 127:025301. [PMID: 34296933 DOI: 10.1103/physrevlett.127.025301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 06/04/2021] [Indexed: 06/13/2023]
Abstract
We use unbiased computational methods to elucidate the onset and properties of pair superfluidity in two-species fermionic and bosonic systems with onsite interspecies attraction loaded in a uniform, i.e., with no confining potential, one-dimensional optical lattice. We compare results from quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG), emphasizing the one-to-one correspondence between the Drude weight tensor, calculated with DMRG, and the various winding numbers extracted from the QMC. Our results show that, for any nonvanishing attractive interaction, pairs form and are the sole contributors to superfluidity; there are no individual contributions due to the separate species. For weak attraction, the pair size diverges exponentially, i.e., Bardeen-Cooper-Schrieffer (BCS) pairing, requiring huge systems to bring out the pair-only nature of the superfluid. This crucial property is largely overlooked in many studies, thereby misinterpreting the origin and nature of the superfluid. We compare and contrast this with the repulsive case and show that the behavior is very different, contradicting previous claims about drag superfluidity and the symmetry of properties for attractive and repulsive interactions. Finally, our results show that the situation is similar for soft-core bosons: superfluidity is due only to pairs, even for the smallest attractive interaction strength compatible with the largest system sizes that we could attain.
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Affiliation(s)
- B Grémaud
- Aix-Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
- Centre for Quantum Technologies, National University of Singapore, 2 Science Drive 3, 117542 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore
| | - G G Batrouni
- Centre for Quantum Technologies, National University of Singapore, 2 Science Drive 3, 117542 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore
- Université Côte d'Azur, INPHYNI, CNRS, 06103 Nice, France
- Beijing Computational Science Research Center, Beijing 100193, China
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10
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Cuestas E, Majtey AP. A generalized molecule approach capturing the Feshbach-induced pairing physics in the BEC-BCS crossover. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:255601. [PMID: 33848988 DOI: 10.1088/1361-648x/abf7a2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 04/13/2021] [Indexed: 06/12/2023]
Abstract
By including the effect of a trap with characteristic energy given by the Fermi temperatureTFin a two-body two-channel model for Feshbach resonances, we reproduce the measured binding energy of ultracold molecules in a40K atomic Fermi gas. We also reproduce the experimental closed-channel fractionZacross the BEC-BCS crossover and into the BCS regime of a6Li atomic Fermi gas. We obtain the expected behaviorZ∝TFat unitarity, together with the recently measured proportionality constant. Our results are also in agreement with recent measurements of theZdependency onTFon the BCS side, where a significant quantitative discrepancy between experimental data and theory's predictions has been repeatedly reported. In order to contrast with future experiments we report the proportionality constant at unitarity betweenZandTFpredicted by our model for a40K atomic Fermi gas.
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Affiliation(s)
- Eloisa Cuestas
- Facultad de Matemática, Astronomía, Física y Computación (FaMAF), Universidad Nacional de Córdoba (UNC), Av. Medina Allende s/n, Ciudad Universitaria, X5000HUA, Córdoba, Argentina
- Instituto de Física Enrique Gaviola (IFEG), Consejo de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Córdoba, Argentina
| | - Ana P Majtey
- Facultad de Matemática, Astronomía, Física y Computación (FaMAF), Universidad Nacional de Córdoba (UNC), Av. Medina Allende s/n, Ciudad Universitaria, X5000HUA, Córdoba, Argentina
- Instituto de Física Enrique Gaviola (IFEG), Consejo de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Córdoba, Argentina
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11
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Luo XW, Zhang C. Spin-Twisted Optical Lattices: Tunable Flat Bands and Larkin-Ovchinnikov Superfluids. PHYSICAL REVIEW LETTERS 2021; 126:103201. [PMID: 33784151 DOI: 10.1103/physrevlett.126.103201] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 12/20/2020] [Accepted: 02/10/2021] [Indexed: 06/12/2023]
Abstract
Moiré superlattices in twisted bilayer graphene and transition-metal dichalcogenides have emerged as a powerful tool for engineering novel band structures and quantum phases of two-dimensional quantum materials. Here we investigate Moiré physics emerging from twisting two independent hexagonal optical lattices of atomic (pseudo-)spin states (instead of bilayers) that exhibit remarkably different physics from twisted bilayer graphene. We employ a momentum-space tight-binding calculation that includes all range real-space tunnelings and show that all twist angles θ≲6° can become magic and support gapped flat bands. Because of the greatly enhanced density of states near the flat bands, the system can be driven to superfluidity by weak attractive interaction. Strikingly, the superfluid phase corresponds to a Larkin-Ovchinnikov state with finite momentum pairing that results from the interplay between flat bands and interspin interactions in the unique single-layer spin-twisted lattice. Our work may pave the way for exploring novel quantum phases and twistronics in cold atomic systems.
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Affiliation(s)
- Xi-Wang Luo
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080-3021, USA
| | - Chuanwei Zhang
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080-3021, USA
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12
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Zaletel MP, Kaufman A, Stamper-Kurn DM, Yao NY. Preparation of Low Entropy Correlated Many-Body States via Conformal Cooling Quenches. PHYSICAL REVIEW LETTERS 2021; 126:103401. [PMID: 33784144 DOI: 10.1103/physrevlett.126.103401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 01/05/2021] [Indexed: 06/12/2023]
Abstract
We propose and analyze a method for preparing low entropy many-body states in isolated quantum optical systems of atoms, ions, and molecules. Our approach is based upon shifting entropy between different regions of a system by spatially modulating the magnitude of the effective Hamiltonian. We conduct two case studies, on a topological spin chain and the spinful fermionic Hubbard model, focusing on the key question: can a "conformal cooling quench" remove sufficient entropy within experimentally accessible timescales? Finite-temperature, time-dependent matrix product state calculations reveal that even moderately sized bath regions can remove enough energy and entropy density to expose coherent low-temperature physics. The protocol is particularly natural in systems with long-range interactions, such as lattice-trapped polar molecules and Rydberg-excited atoms, where the magnitude of the Hamiltonian scales directly with the interparticle spacing. To this end, we propose simple, near-term implementations of conformal cooling quenches in systems of atoms or molecules, where signatures of low-temperature phases may be observed.
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Affiliation(s)
- Michael P Zaletel
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
| | - Adam Kaufman
- JILA, University of Colorado and National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Dan M Stamper-Kurn
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
| | - Norman Y Yao
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
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13
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Jahromi SS, Orús R. Thermal bosons in 3d optical lattices via tensor networks. Sci Rep 2020; 10:19051. [PMID: 33149156 PMCID: PMC7642398 DOI: 10.1038/s41598-020-75548-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 10/13/2020] [Indexed: 11/26/2022] Open
Abstract
Ultracold atoms in optical lattices are one of the most promising experimental setups to simulate strongly correlated systems. However, efficient numerical algorithms able to benchmark experiments at low-temperatures in interesting 3d lattices are lacking. To this aim, here we introduce an efficient tensor network algorithm to accurately simulate thermal states of local Hamiltonians in any infinite lattice, and in any dimension. We apply the method to simulate thermal bosons in optical lattices. In particular, we study the physics of the (soft-core and hard-core) Bose–Hubbard model on the infinite pyrochlore and cubic lattices with unprecedented accuracy. Our technique is therefore an ideal tool to benchmark realistic and interesting optical-lattice experiments.
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Affiliation(s)
- Saeed S Jahromi
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018, San Sebastián, Spain
| | - Román Orús
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018, San Sebastián, Spain. .,Ikerbasque Foundation for Science, Maria Diaz de Haro 3, 48013, Bilbao, Spain. .,Multiverse Computing, Paseo de Miramón 170, 20014, San Sebastián, Spain.
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14
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Yamamoto K, Nakagawa M, Adachi K, Takasan K, Ueda M, Kawakami N. Theory of Non-Hermitian Fermionic Superfluidity with a Complex-Valued Interaction. PHYSICAL REVIEW LETTERS 2019; 123:123601. [PMID: 31633989 DOI: 10.1103/physrevlett.123.123601] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Indexed: 06/10/2023]
Abstract
Motivated by recent experimental advances in ultracold atoms, we analyze a non-Hermitian (NH) BCS Hamiltonian with a complex-valued interaction arising from inelastic scattering between fermions. We develop a mean-field theory to obtain a NH gap equation for order parameters, which are different from the standard BCS ones due to the inequivalence of left and right eigenstates in the NH physics. We find unconventional phase transitions unique to NH systems: superfluidity shows reentrant behavior with increasing dissipation, as a consequence of nondiagonalizable exceptional points, lines, and surfaces in the quasiparticle Hamiltonian for weak attractive interactions. For strong attractive interactions, the superfluid gap never collapses but is enhanced by dissipation due to an interplay between the BCS-BEC crossover and the quantum Zeno effect. Our results lay the groundwork for studies of fermionic superfluidity subject to inelastic collisions.
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Affiliation(s)
- Kazuki Yamamoto
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Masaya Nakagawa
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
- Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Kyosuke Adachi
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Hyogo, 650-0047, Japan
| | - Kazuaki Takasan
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - Masahito Ueda
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
- Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Norio Kawakami
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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15
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Mukherjee B, Patel PB, Yan Z, Fletcher RJ, Struck J, Zwierlein MW. Spectral Response and Contact of the Unitary Fermi Gas. PHYSICAL REVIEW LETTERS 2019; 122:203402. [PMID: 31172778 DOI: 10.1103/physrevlett.122.203402] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Indexed: 06/09/2023]
Abstract
We measure radio frequency (rf) spectra of the homogeneous unitary Fermi gas at temperatures ranging from the Boltzmann regime through quantum degeneracy and across the superfluid transition. For all temperatures, a single spectral peak is observed. Its position smoothly evolves from the bare atomic resonance in the Boltzmann regime to a frequency corresponding to nearly one Fermi energy at the lowest temperatures. At high temperatures, the peak width reflects the scattering rate of the atoms, while at low temperatures, the width is set by the size of fermion pairs. Above the superfluid transition, and approaching the quantum critical regime, the width increases linearly with temperature, indicating non-Fermi-liquid behavior. From the wings of the rf spectra, we obtain the contact, quantifying the strength of short-range pair correlations. We find that the contact rapidly increases as the gas is cooled below the superfluid transition.
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Affiliation(s)
- Biswaroop Mukherjee
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Parth B Patel
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Zhenjie Yan
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Richard J Fletcher
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Julian Struck
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Département de Physique, Ecole Normale Supérieure / PSL Research University, CNRS, 24 rue Lhomond, 75005 Paris, France
| | - Martin W Zwierlein
- MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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16
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Park JW, Ko B, Shin Y. Critical Vortex Shedding in a Strongly Interacting Fermionic Superfluid. PHYSICAL REVIEW LETTERS 2018; 121:225301. [PMID: 30547641 DOI: 10.1103/physrevlett.121.225301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Indexed: 06/09/2023]
Abstract
We study the critical vortex shedding in a strongly interacting fermionic superfluid of ^{6}Li across the BEC-BCS crossover. By moving an optical obstacle in the sample and directly imaging the vortices after the time of flight, the critical velocity u_{vor} for vortex shedding is measured as a function of the obstacle travel distance L. The observed u_{vor} increases with decreasing L, where the rate of increase is the highest in the unitary regime. In the deep Bose-Einstein condensation regime, an empirical dissipation model well captures the dependence of u_{vor} on L, characterized by a constant value of η=-[d(1/u_{vor})/d(1/L)]. However, as the system is tuned across the resonance, a step increase of η develops about a characteristic distance L_{c} as L is increased, where L_{c} is comparable to the obstacle size. This bimodal behavior is strengthened as the system is tuned towards the BCS regime. We attribute this evolution of u_{vor} to the emergence of the underlying fermionic degree of freedom in the vortex-shedding dynamics of a Fermi condensate.
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Affiliation(s)
- Jee Woo Park
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
| | - Bumsuk Ko
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
- Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea
| | - Y Shin
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
- Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea
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17
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Hu H, Zhang F, Zhang C. Majorana Doublets, Flat Bands, and Dirac Nodes in s-Wave Superfluids. PHYSICAL REVIEW LETTERS 2018; 121:185302. [PMID: 30444404 DOI: 10.1103/physrevlett.121.185302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Revised: 08/14/2018] [Indexed: 06/09/2023]
Abstract
Topological superfluids protected by mirror and time-reversal symmetries are exotic states of matter possessing Majorana Kramers pairs (MKPs), yet their realizations have long been hindered by the requirement of unconventional pairing. We propose to realize such a topological superfluid by utilizing s-wave pairing and emergent mirror and time-reversal symmetries in two coupled 1D ultracold atomic Fermi gases with spin-orbit coupling. By stacking such systems into 2D, we discover topological and Dirac-nodal superfluids hosting distinct MKP flat bands. We show that the emergent symmetries make the MKPs and their flat bands stable against pairing fluctuations that otherwise annihilate Majorana pairs. Exploiting new experimental developments, our scheme provides a unique platform for exploring MKPs and their applications in quantum computation.
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Affiliation(s)
- Haiping Hu
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, USA
| | - Fan Zhang
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, USA
| | - Chuanwei Zhang
- Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, USA
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18
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Ptok A, Cichy A, Domański T. Quantum engineering of Majorana quasiparticles in one-dimensional optical lattices. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:355602. [PMID: 30051875 DOI: 10.1088/1361-648x/aad659] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We propose a feasible way of engineering Majorana-type quasiparticles in ultracold fermionic gases on a one-dimensional (1D) optical lattice. For this purpose, imbalanced ultracold atoms interacting by the spin-orbit coupling should be hybridized with a three-dimensional Bose-Einstein condensate molecular cloud. We show that the Majorana-type excitations can be created or annihilated upon constraining the profile of a trapping potential and/or an internal scattering barier. This process is modeled within the Bogoliubov-de Gennes approach. Our study is relevant also to nanoscopic 1D superconductors, where both potentials can be imposed by electrostatic means.
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Affiliation(s)
- Andrzej Ptok
- Institute of Nuclear Physics, Polish Academy of Sciences, ul. E. Radzikowskiego 152, PL-31342 Kraków, Poland
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19
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Shkedrov C, Florshaim Y, Ness G, Gandman A, Sagi Y. High-Sensitivity rf Spectroscopy of a Strongly Interacting Fermi Gas. PHYSICAL REVIEW LETTERS 2018; 121:093402. [PMID: 30230882 DOI: 10.1103/physrevlett.121.093402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 06/25/2018] [Indexed: 06/08/2023]
Abstract
rf spectroscopy is one of the most powerful probing techniques in the field of ultracold gases. We report on a novel rf spectroscopy scheme with which we can detect very weak signals of only a few atoms. Using this method, we extended the experimentally accessible photon-energies range by an order of magnitude compared to previous studies. We directly verify a universal property of fermions with short-range interactions which is a power-law scaling of the rf spectrum tail all the way up to the interaction scale. We also determine, with high precision, the trap average contact parameter for different interaction strength. Finally, we employ our technique to precisely measure the binding energy of Feshbach molecules in an extended range of magnetic fields. These data are used to extract a new calibration of the Feshbach resonance between the two lowest energy levels of ^{40}K.
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Affiliation(s)
- Constantine Shkedrov
- Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Yanay Florshaim
- Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Gal Ness
- Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Andrey Gandman
- Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Yoav Sagi
- Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
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20
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Mueller EJ. Review of pseudogaps in strongly interacting Fermi gases. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:104401. [PMID: 28686169 DOI: 10.1088/1361-6633/aa7e53] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A central challenge in modern condensed matter physics is developing the tools for understanding nontrivial yet unordered states of matter. One important idea to emerge in this context is that of a 'pseudogap': the fact that under appropriate circumstances the normal state displays a suppression of the single particle spectral density near the Fermi level, reminiscent of the gaps seen in ordered states of matter. While these concepts arose in a solid state context, they are now being explored in cold gases. This article reviews the current experimental and theoretical understanding of the normal state of strongly interacting Fermi gases, with particular focus on the phenomonology which is traditionally associated with the pseudogap.
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Affiliation(s)
- Erich J Mueller
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca NY 14853, United States of America
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21
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Above-threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider. Nat Commun 2017; 8:452. [PMID: 28878374 PMCID: PMC5587761 DOI: 10.1038/s41467-017-00458-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 06/29/2017] [Indexed: 11/13/2022] Open
Abstract
Ultracold atomic gases have realized numerous paradigms of condensed matter physics, where control over interactions has crucially been afforded by tunable Feshbach resonances. So far, the characterization of these Feshbach resonances has almost exclusively relied on experiments in the threshold regime near zero energy. Here, we use a laser-based collider to probe a narrow magnetic Feshbach resonance of rubidium above threshold. By measuring the overall atomic loss from colliding clouds as a function of magnetic field, we track the energy-dependent resonance position. At higher energy, our collider scheme broadens the loss feature, making the identification of the narrow resonance challenging. However, we observe that the collisions give rise to shifts in the center-of-mass positions of outgoing clouds. The shifts cross zero at the resonance and this allows us to accurately determine its location well above threshold. Our inferred resonance positions are in excellent agreement with theory. Studies on energy-dependent scattering of ultracold atoms were previously carried out near zero collision energies. Here, the authors observe a magnetic Feshbach resonance in ultracold Rb collisions for above-threshold energies and their method can also be used to detect higher partial wave resonances.
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22
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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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23
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24
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Krauser JS, Heinze J, Götze S, Langbecker M, Fläschner N, Cook L, Hanna TM, Tiesinga E, Sengstock K, Becker C. Investigation of Feshbach resonances in ultracold 40K spin mixtures. PHYSICAL REVIEW. A 2017; 95:042701. [PMID: 29876533 PMCID: PMC5986192 DOI: 10.1103/physreva.95.042701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Magnetically tunable Feshbach resonances are an indispensable tool for experiments with atomic quantum gases. We report on 37 thus far unpublished Feshbach resonances and four further probable Feshbach resonances in spin mixtures of ultracold fermionic 40K with temperatures well below 100 nK. In particular, we locate a broad resonance at B = 389.7G with a magnetic width of 26.7 G. Here 1 G = 10-4 T. Furthermore, by exciting low-energy spin waves, we demonstrate a means to precisely determine the zero crossing of the scattering length for this broad Feshbach resonance. Our findings allow for further tunability in experiments with ultracold 40K quantum gases.
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Affiliation(s)
- J. S. Krauser
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - J. Heinze
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - S. Götze
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - M. Langbecker
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Institut für Physik, Johannes Gutenberg Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
| | - N. Fläschner
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - L. Cook
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - T. M. Hanna
- Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899, USA
| | - E. Tiesinga
- Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899, USA
| | - K. Sengstock
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - C. Becker
- Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
- Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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25
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Chen MN, Mei F, Su W, Wang HQ, Zhu SL, Sheng L, Xing DY. Topological phases of the kicked Harper-Kitaev model with ultracold atoms. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:035601. [PMID: 27845928 DOI: 10.1088/0953-8984/29/3/035601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We propose using ultracold atoms trapped in a one-dimensional periodically driven optical lattice to realize the Harper-Kitaev model, where the on-site energies are periodically kicked. Such a system provides a natural platform to study both Chern insulators and Majorana fermions. Based on calculating the quasienergy spectra, we find that both Floquet Majorana modes and Hall chiral edge modes could appear at the sample boundary in the gaps between the quasienergy bands. We also study the competition of topological superconductor and Chern insulator states in the model. We calculate the [Formula: see text] index and Floquet Chern number to characterize the above two different topological states, including the topological phase transitions in the kicked Harper-Kitaev model with the increase in the strength of the kick.
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Affiliation(s)
- M N Chen
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
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26
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Łącki M, Baranov MA, Pichler H, Zoller P. Nanoscale "Dark State" Optical Potentials for Cold Atoms. PHYSICAL REVIEW LETTERS 2016; 117:233001. [PMID: 27982643 DOI: 10.1103/physrevlett.117.233001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Indexed: 06/06/2023]
Abstract
We discuss the generation of subwavelength optical barriers on the scale of tens of nanometers, as conservative optical potentials for cold atoms. These arise from nonadiabatic corrections to Born-Oppenheimer potentials from dressed "dark states" in atomic Λ configurations. We illustrate the concepts with a double layer potential for atoms obtained from inserting an optical subwavelength barrier into a well generated by an off-resonant optical lattice, and discuss bound states of pairs of atoms interacting via magnetic dipolar interactions. The subwavelength optical barriers represent an optical "Kronig-Penney" potential. We present a detailed study of the band structure in optical Kronig-Penney potentials, including decoherence from spontaneous emission and atom loss to open "bright" channels.
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Affiliation(s)
- M Łącki
- Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria
- Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
| | - M A Baranov
- Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria
- Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
| | - H Pichler
- Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria
- Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
- ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
- Physics Department, Harvard University, 17 Oxford Street, Cambridge, Massachusetts 02138, USA
| | - P Zoller
- Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria
- Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
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27
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Boettcher I, Bayha L, Kedar D, Murthy PA, Neidig M, Ries MG, Wenz AN, Zürn G, Jochim S, Enss T. Equation of State of Ultracold Fermions in the 2D BEC-BCS Crossover Region. PHYSICAL REVIEW LETTERS 2016; 116:045303. [PMID: 26871341 DOI: 10.1103/physrevlett.116.045303] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 06/05/2023]
Abstract
We report the experimental measurement of the equation of state of a two-dimensional Fermi gas with attractive s-wave interactions throughout the crossover from a weakly coupled Fermi gas to a Bose gas of tightly bound dimers as the interaction strength is varied. We demonstrate that interactions lead to a renormalization of the density of the Fermi gas by several orders of magnitude. We compare our data near the ground state and at finite temperature with predictions for both fermions and bosons from quantum Monte Carlo simulations and Luttinger-Ward theory. Our results serve as input for investigations of close-to-equilibrium dynamics and transport in the two-dimensional system.
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Affiliation(s)
- I Boettcher
- Institute for Theoretical Physics, Heidelberg University, D-69120 Heidelberg, Germany
| | - L Bayha
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - D Kedar
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - P A Murthy
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - M Neidig
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - M G Ries
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - A N Wenz
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - G Zürn
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - S Jochim
- Physikalisches Institut, Heidelberg University, D-69120 Heidelberg, Germany
| | - T Enss
- Institute for Theoretical Physics, Heidelberg University, D-69120 Heidelberg, Germany
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28
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Höfer M, Riegger L, Scazza F, Hofrichter C, Fernandes DR, Parish MM, Levinsen J, Bloch I, Fölling S. Observation of an Orbital Interaction-Induced Feshbach Resonance in (173)Yb. PHYSICAL REVIEW LETTERS 2015; 115:265302. [PMID: 26765000 DOI: 10.1103/physrevlett.115.265302] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Indexed: 06/05/2023]
Abstract
We report on the experimental observation of a novel interorbital Feshbach resonance in ultracold (173)Yb atoms. This opens up the possibility of tuning the interactions between the (1)S(0) and (3)P(0) metastable state, both possessing zero total electronic angular momentum. The resonance is observed at experimentally accessible magnetic field strengths and occurs universally for all hyperfine state combinations. We characterize the resonance in the bulk via interorbital cross thermalization as well as in a three-dimensional lattice using high-resolution clock-line spectroscopy. Our measurements are well described by a generalized two-channel model of the orbital-exchange interactions.
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Affiliation(s)
- M Höfer
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - L Riegger
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - F Scazza
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - C Hofrichter
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - D R Fernandes
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - M M Parish
- School of Physics and Astronomy, Monash University, Victoria 3800, Australia
| | - J Levinsen
- School of Physics and Astronomy, Monash University, Victoria 3800, Australia
| | - I Bloch
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - S Fölling
- Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
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29
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Conradson SD, Gilbertson SM, Daifuku SL, Kehl JA, Durakiewicz T, Andersson DA, Bishop AR, Byler DD, Maldonado P, Oppeneer PM, Valdez JA, Neidig ML, Rodriguez G. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation. Sci Rep 2015; 5:15278. [PMID: 26472071 PMCID: PMC4607891 DOI: 10.1038/srep15278] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 09/21/2015] [Indexed: 11/23/2022] Open
Abstract
Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.
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Affiliation(s)
- Steven D Conradson
- Synchrotron Soleil, L'Orme des Merisiers Saint-Aubin, BP 48 91192, Gif-sur-Yvette, France
| | | | | | - Jeffrey A Kehl
- Department of Chemistry, University of Rochester, NY 14627, USA
| | - Tomasz Durakiewicz
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - David A Andersson
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Alan R Bishop
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Darrin D Byler
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Pablo Maldonado
- Department of Physics and Astronomy, Uppsala University, S-75120, Uppsala, Sweden
| | - Peter M Oppeneer
- Department of Physics and Astronomy, Uppsala University, S-75120, Uppsala, Sweden
| | - James A Valdez
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | | | - George Rodriguez
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
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Doggen EVH, Kinnunen JJ. Momentum-resolved spectroscopy of a Fermi liquid. Sci Rep 2015; 5:9539. [PMID: 25941948 PMCID: PMC5386214 DOI: 10.1038/srep09539] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 03/10/2015] [Indexed: 12/02/2022] Open
Abstract
We consider a recent momentum-resolved radio-frequency spectroscopy experiment, in which Fermi liquid properties of a strongly interacting atomic Fermi gas were studied. Here we show that by extending the Brueckner-Goldstone model, we can formulate a theory that goes beyond basic mean-field theories and that can be used for studying spectroscopies of dilute atomic gases in the strongly interacting regime. The model hosts well-defined quasiparticles and works across a wide range of temperatures and interaction strengths. The theory provides excellent qualitative agreement with the experiment. Comparing the predictions of the present theory with the mean-field Bardeen-Cooper-Schrieffer theory yields insights into the role of pair correlations, Tan's contact, and the Hartree mean-field energy shift.
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Affiliation(s)
- Elmer V. H. Doggen
- COMP Centre of Excellence and Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
| | - Jami J. Kinnunen
- COMP Centre of Excellence and Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
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31
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Miake Y, Mukaiyama T, O'Hara KM, Gensemer S. A self-injected, diode-pumped, solid-state ring laser for laser cooling of Li atoms. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:043113. [PMID: 25933847 DOI: 10.1063/1.4917558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have constructed a solid-state light source for experiments with laser cooled lithium atoms based on a Nd:YVO4 ring laser with second-harmonic generation. Unidirectional lasing, an improved mode selection, and a high output power of the ring laser were achieved by weak coupling to an external cavity which contained the lossy elements required for single frequency operation. Continuous frequency tuning is accomplished by controlling two piezoelectric transducers (PZTs) in the internal and the external cavities simultaneously. The light source has been utilized to trap and cool fermionic lithium atoms into the quantum degenerate regime.
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Affiliation(s)
- Yudai Miake
- Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
| | - Takashi Mukaiyama
- Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
| | - Kenneth M O'Hara
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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32
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Braun J, Drut JE, Roscher D. Zero-temperature equation of state of mass-imbalanced resonant Fermi gases. PHYSICAL REVIEW LETTERS 2015; 114:050404. [PMID: 25699425 DOI: 10.1103/physrevlett.114.050404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Indexed: 06/04/2023]
Abstract
We calculate the zero-temperature equation of state of mass-imbalanced resonant Fermi gases in an ab initio fashion, by implementing the recent proposal of imaginary-valued mass difference to bypass the sign problem in lattice Monte Carlo calculations. The fully nonperturbative results thus obtained are analytically continued to real mass-imbalance to yield the physical equation of state, providing predictions for upcoming experiments with mass-imbalanced atomic Fermi gases. In addition, we present an exact relation for the rate of change of the equation of state at small mass imbalances, showing that it is fully determined by the energy of the mass-balanced system.
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Affiliation(s)
- Jens Braun
- Institut für Kernphysik (Theoriezentrum), Technische Universität Darmstadt, D-64289 Darmstadt, Germany and ExtreMe Matter Institute EMMI, GSI, Planckstraße 1, D-64291 Darmstadt, Germany
| | - Joaquín E Drut
- Institut für Kernphysik (Theoriezentrum), Technische Universität Darmstadt, D-64289 Darmstadt, Germany and ExtreMe Matter Institute EMMI, GSI, Planckstraße 1, D-64291 Darmstadt, Germany and Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Dietrich Roscher
- Institut für Kernphysik (Theoriezentrum), Technische Universität Darmstadt, D-64289 Darmstadt, Germany
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33
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Gopalakrishnan S, Parker CV, Demler E. Mobile magnetic impurities in a Fermi superfluid: a route to designer molecules. PHYSICAL REVIEW LETTERS 2015; 114:045301. [PMID: 25679897 DOI: 10.1103/physrevlett.114.045301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Indexed: 06/04/2023]
Abstract
A magnetic impurity in a fermionic superfluid hosts bound quasiparticle states known as Yu-Shiba-Rusinov states. We argue here that, if the impurity is mobile (i.e., has a finite mass), the impurity and its bound Yu-Shiba-Rusinov quasiparticle move together as a midgap molecule, which has an unusual "Mexican-hat" dispersion that is tunable via the fermion density. We map out the impurity dispersion, which consists of an "atomic" branch (in which the impurity is dressed by quasiparticle pairs) and a "molecular" branch (in which the impurity binds a quasiparticle). We discuss the experimental realization and detection of midgap Shiba molecules, focusing on Li-Cs mixtures, and comment on the prospects they offer for realizing exotic many-body states.
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Affiliation(s)
| | - Colin V Parker
- James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
| | - Eugene Demler
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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34
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Cooling a band insulator with a metal: fermionic superfluid in a dimerized holographic lattice. Sci Rep 2014; 4:6655. [PMID: 25324029 PMCID: PMC4200405 DOI: 10.1038/srep06655] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 09/19/2014] [Indexed: 11/08/2022] Open
Abstract
A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces a band insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal "cools" the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature - even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states.
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35
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Semczuk M, Gunton W, Bowden W, Madison KW. Anomalous behavior of dark states in quantum gases of (6)Li. PHYSICAL REVIEW LETTERS 2014; 113:055302. [PMID: 25126925 DOI: 10.1103/physrevlett.113.055302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Indexed: 06/03/2023]
Abstract
We create atom-molecule dark states in a degenerate Fermi gas of ^{6}Li in both weakly and strongly interacting regimes using two-photon Raman scattering to couple fermion pairs to bound molecular states in the ground singlet and triplet potential. Near the unitarity point in the BEC-BCS crossover regime, the atom number revival height associated with the dark state abruptly and unexpectedly decreases and remains low for magnetic fields below the Feshbach resonance center at 832.2 G. With a weakly interacting Fermi gas at 0 G, we perform precision dark-state spectroscopy of the least-bound vibrational levels of the lowest singlet and triplet potentials. From these spectra, we obtain binding energies of the v^{''}=9, N^{''}=0 level of the a(1^{3}Σ_{u}^{+}) potential and the v^{''}=38, N^{''}=0 level of the X(1^{1}Σ_{g}^{+}) potential with absolute uncertainty as low as 20 kHz. For the triplet potential, we resolve the molecular hyperfine structure.
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Affiliation(s)
- Mariusz Semczuk
- Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada
| | - Will Gunton
- Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada
| | - William Bowden
- Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada
| | - Kirk W Madison
- Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada
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36
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Massignan P, Zaccanti M, Bruun GM. Polarons, dressed molecules and itinerant ferromagnetism in ultracold Fermi gases. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2014; 77:034401. [PMID: 24553400 DOI: 10.1088/0034-4885/77/3/034401] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this review, we discuss the properties of a few impurity atoms immersed in a gas of ultracold fermions--the so-called Fermi polaron problem. On one hand, this many-body system is appealing because it can be described almost exactly with simple diagrammatic and/or variational theoretical approaches. On the other, it provides a quantitatively reliable insight into the phase diagram of strongly interacting population-imbalanced quantum mixtures. In particular, we show that the polaron problem can be applied to the study of itinerant ferromagnetism, a long-standing problem in quantum mechanics.
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Affiliation(s)
- Pietro Massignan
- ICFO-Institut de Ciències Fotòniques, Mediterranean Technology Park, E-08860 Castelldefels, Barcelona, Spain
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37
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Roy A, Dasgupta R, Modak S, Das A, Sengupta K. Periodic dynamics of fermionic superfluids in the BCS regime. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:205703. [PMID: 23628739 DOI: 10.1088/0953-8984/25/20/205703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We study the zero temperature non-equilibrium dynamics of a fermionic superfluid in the BCS limit and in the presence of a drive leading to a time-dependent chemical potential μ(t). We choose a periodic driving protocol characterized by a frequency ω and compute the fermion density, the wavefunction overlap, and the residual energy of the system at the end of N periods of the drive. We demonstrate that the BCS self-consistency condition is crucial in shaping the long time behaviour of the fermions subjected to the drive and provide an analytical understanding of the behaviour of the fermion density nkF (where kF is the Fermi momentum vector) after a drive period and for large ω. We also show that the momentum distribution of the excitations generated due to such a drive bears the signature of the pairing symmetry and can be used, for example, to distinguish between s- and d-wave superfluids. We propose experiments to test our theory.
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Affiliation(s)
- A Roy
- TCMP Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064, India
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38
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Zürn G, Lompe T, Wenz AN, Jochim S, Julienne PS, Hutson JM. Precise characterization of 6Li Feshbach resonances using trap-sideband-resolved RF spectroscopy of weakly bound molecules. PHYSICAL REVIEW LETTERS 2013; 110:135301. [PMID: 23581332 DOI: 10.1103/physrevlett.110.135301] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Indexed: 06/02/2023]
Abstract
We perform radio-frequency dissociation spectroscopy of weakly bound 6Li2 Feshbach molecules using low-density samples of about 30 molecules in an optical dipole trap. Combined with a high magnetic field stability, this allows us to resolve the discrete trap levels in the radio-frequency dissociation spectra. This novel technique allows the binding energy of Feshbach molecules to be determined with unprecedented precision. We use these measurements as an input for a fit to the 6Li scattering potential using coupled-channel calculations. From this new potential, we determine the pole positions of the broad 6Li Feshbach resonances with an accuracy better than 7×10(-4) of the resonance widths. This eliminates the dominant uncertainty for current precision measurements of the equation of state of strongly interacting Fermi gases. As an important consequence, our results imply a corrected value for the Bertsch parameter ξ measured by Ku et al. [Science 335, 563 (2012)], which is ξ=0.370(5)(8).
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Affiliation(s)
- G Zürn
- Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, 69120 Heidelberg, Germany
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39
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Volčko D, Quader KF. Signatures of fermion pairing with unconventional symmetry around the BCS-BEC crossover in a quasi-2D lattice. PHYSICAL REVIEW LETTERS 2012; 109:235303. [PMID: 23368217 DOI: 10.1103/physrevlett.109.235303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2012] [Indexed: 06/01/2023]
Abstract
We consider fermions on a 2D square lattice with a finite-range pairing interaction, and obtain signatures for unconventional pair-symmetry states, d(x(2)-y(2)) and extended-s (s(*)), in the Bardeen-Cooper-Schrieffer-Bose-Einstein Condensation crossover region. We find that the fermion momentum distribution function, v(k)(2), the ratio of the Bogoliubov coefficients, v(k)/u(k), and the Fourier transform of v(k)(2) are strikingly different for d and s(*) symmetries in the crossover region. The chemical potential and the gap functions for both pairing symmetries show several interesting features as a function of interaction. Fermionic atoms in 2D optical lattices may provide a way to test these signatures. We discuss current generation cold atom experiments that may be utilized.
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Affiliation(s)
- Dušan Volčko
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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40
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Kohstall C, Zaccanti M, Jag M, Trenkwalder A, Massignan P, Bruun GM, Schreck F, Grimm R. Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture. Nature 2012; 485:615-8. [DOI: 10.1038/nature11065] [Citation(s) in RCA: 330] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2011] [Accepted: 03/09/2012] [Indexed: 11/09/2022]
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41
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Hutzler NR, Lu HI, Doyle JM. The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules. Chem Rev 2012; 112:4803-27. [PMID: 22571401 DOI: 10.1021/cr200362u] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nicholas R. Hutzler
- Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts
02138, United States
| | - Hsin-I Lu
- Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts
02138, United States
| | - John M. Doyle
- Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts
02138, United States
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42
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Langmack C, Barth M, Zwerger W, Braaten E. Clock shift in a strongly interacting two-dimensional Fermi gas. PHYSICAL REVIEW LETTERS 2012; 108:060402. [PMID: 22401040 DOI: 10.1103/physrevlett.108.060402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Indexed: 05/31/2023]
Abstract
We derive universal relations for the rf spectroscopy of a two-dimensional Fermi gas consisting of two spin states interacting through an S-wave scattering length. The rf transition rate has a high-frequency tail that is proportional to the contact and displays logarithmic scaling violations, decreasing asymptotically like 1/(ω2ln2ω). Its coefficient is proportional to ln2'(a'(2D)/a(2D)), where a(2D) and a'(2D) are the two-dimensional scattering lengths associated with initial-state and final-state interactions. The clock shift is proportional to the contact and to ln(a'(2D)/a(2D)). If |ln(a'(2D)/a(2D))| >> 1, the clock shift arises as a cancellation between much larger contributions proportional to ln2(a'(2D)/a(2D)) from bound-bound and bound-free rf transitions.
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Affiliation(s)
- Christian Langmack
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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43
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44
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The BCS–BEC Crossover and the Unitary Fermi Gas. THE BCS-BEC CROSSOVER AND THE UNITARY FERMI GAS 2012. [DOI: 10.1007/978-3-642-21978-8_1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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45
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Jiang L, Kitagawa T, Alicea J, Akhmerov AR, Pekker D, Refael G, Cirac JI, Demler E, Lukin MD, Zoller P. Majorana fermions in equilibrium and in driven cold-atom quantum wires. PHYSICAL REVIEW LETTERS 2011; 106:220402. [PMID: 21702583 DOI: 10.1103/physrevlett.106.220402] [Citation(s) in RCA: 170] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2011] [Revised: 04/27/2011] [Indexed: 05/31/2023]
Abstract
We introduce a new approach to create and detect Majorana fermions using optically trapped 1D fermionic atoms. In our proposed setup, two internal states of the atoms couple via an optical Raman transition-simultaneously inducing an effective spin-orbit interaction and magnetic field-while a background molecular BEC cloud generates s-wave pairing for the atoms. The resulting cold-atom quantum wire supports Majorana fermions at phase boundaries between topologically trivial and nontrivial regions, as well as "Floquet Majorana fermions" when the system is periodically driven. We analyze experimental parameters, detection schemes, and various imperfections.
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Affiliation(s)
- Liang Jiang
- Institute for Quantum Information, California Institute of Technology, Pasadena, California 91125, USA
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46
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Fröhlich B, Feld M, Vogt E, Koschorreck M, Zwerger W, Köhl M. Radio-frequency spectroscopy of a strongly interacting two-dimensional Fermi gas. PHYSICAL REVIEW LETTERS 2011; 106:105301. [PMID: 21469798 DOI: 10.1103/physrevlett.106.105301] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Revised: 01/13/2011] [Indexed: 05/30/2023]
Abstract
We realize and study a strongly interacting two-component atomic Fermi gas confined to two dimensions in an optical lattice. Using radio-frequency spectroscopy we measure the interaction energy of the strongly interacting gas. We observe the confinement-induced Feshbach resonance on the attractive side of the 3D Feshbach resonance and find the existence of confinement-induced molecules in very good agreement with theoretical predictions.
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Affiliation(s)
- Bernd Fröhlich
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB30HE, United Kingdom
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47
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Heikkinen MOJ, Massel F, Kajala J, Leskinen MJ, Paraoanu GS, Törmä P. Spin-asymmetric Josephson effect. PHYSICAL REVIEW LETTERS 2010; 105:225301. [PMID: 21231393 DOI: 10.1103/physrevlett.105.225301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 09/03/2010] [Indexed: 05/30/2023]
Abstract
We propose that with ultracold Fermi gases one can realize a spin-asymmetric Josephson effect in which the two spin components of a Cooper pair are driven asymmetrically--corresponding to driving a Josephson junction of two superconductors with different voltages V(↑) and V(↓) for spin up and down electrons, respectively. We predict that the spin up and down components oscillate at the same frequency but with different amplitudes. Furthermore our results reveal that the standard interpretation of the Josephson supercurrent in terms of coherent bosonic pair tunneling is insufficient. We provide an intuitive interpretation of the Josephson supercurrent as interference in Rabi oscillations of pairs and single particles, the latter causing the asymmetry.
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Affiliation(s)
- M O J Heikkinen
- Department of Applied Physics, Aalto University School of Science and Technology, P.O.Box 15100, FI-00076 Aalto, Finland
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48
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Song JL, Mashayekhi MS, Zhou F. Fermi-Bose mixtures near broad interspecies Feshbach resonances. PHYSICAL REVIEW LETTERS 2010; 105:195301. [PMID: 21231180 DOI: 10.1103/physrevlett.105.195301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 05/31/2010] [Indexed: 05/30/2023]
Abstract
In this Letter we study dressed bound states in Fermi-Bose mixtures near broad interspecies resonances, and implications on many-body correlations. We present the evidence for a first order phase transition between a mixture of Fermi gas and condensate, and a fully paired mixture where extended fermionic molecules occupy a single pairing channel instead of forming a molecular Fermi surface. We further investigate the effect of Fermi surface dynamics and pair fluctuations and discuss the validity of our results.
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Affiliation(s)
- Jun Liang Song
- Department of Physics and Astronomy, The University of British Columbia, Vancouver, B.C., Canada V6T1Z1
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49
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Affiliation(s)
- Jeremy M. Hutson
- a Department of Chemistry , University of Durham , South Road, Durham , DH1 3LE , England
| | - Pavel Soldán
- b Faculty of Nuclear Sciences and Physical Engineering , Department of Physics , Doppler Institute , Czech Technical University , Břehová 7 , 115 19 Praha 1 , Czech Republic
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50
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DeSalvo BJ, Yan M, Mickelson PG, Martinez de Escobar YN, Killian TC. Degenerate Fermi gas of (87)Sr. PHYSICAL REVIEW LETTERS 2010; 105:030402. [PMID: 20867747 DOI: 10.1103/physrevlett.105.030402] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2010] [Indexed: 05/29/2023]
Abstract
We report quantum degeneracy in a gas of ultracold fermionic (87)Sr atoms. By evaporatively cooling a mixture of spin states in an optical dipole trap for 10.5 s, we obtain samples well into the degenerate regime with T/T(F)=0.26(-0.06)(+0.05). The main signature of degeneracy is a change in the momentum distribution as measured by time-of-flight imaging, and we also observe a decrease in evaporation efficiency below T/T(F) ∼0.5.
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Affiliation(s)
- B J DeSalvo
- Department of Physics and Astronomy, Rice University, Houston, Texas, 77251, USA
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