1
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Huang JY, Su RY, Lim WH, Feng M, van Straaten B, Severin B, Gilbert W, Dumoulin Stuyck N, Tanttu T, Serrano S, Cifuentes JD, Hansen I, Seedhouse AE, Vahapoglu E, Leon RCC, Abrosimov NV, Pohl HJ, Thewalt MLW, Hudson FE, Escott CC, Ares N, Bartlett SD, Morello A, Saraiva A, Laucht A, Dzurak AS, Yang CH. High-fidelity spin qubit operation and algorithmic initialization above 1 K. Nature 2024; 627:772-777. [PMID: 38538941 PMCID: PMC10972758 DOI: 10.1038/s41586-024-07160-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 02/05/2024] [Indexed: 04/01/2024]
Abstract
The encoding of qubits in semiconductor spin carriers has been recognized as a promising approach to a commercial quantum computer that can be lithographically produced and integrated at scale1-10. However, the operation of the large number of qubits required for advantageous quantum applications11-13 will produce a thermal load exceeding the available cooling power of cryostats at millikelvin temperatures. As the scale-up accelerates, it becomes imperative to establish fault-tolerant operation above 1 K, at which the cooling power is orders of magnitude higher14-18. Here we tune up and operate spin qubits in silicon above 1 K, with fidelities in the range required for fault-tolerant operations at these temperatures19-21. We design an algorithmic initialization protocol to prepare a pure two-qubit state even when the thermal energy is substantially above the qubit energies and incorporate radiofrequency readout to achieve fidelities up to 99.34% for both readout and initialization. We also demonstrate single-qubit Clifford gate fidelities up to 99.85% and a two-qubit gate fidelity of 98.92%. These advances overcome the fundamental limitation that the thermal energy must be well below the qubit energies for the high-fidelity operation to be possible, surmounting a main obstacle in the pathway to scalable and fault-tolerant quantum computation.
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Affiliation(s)
- Jonathan Y Huang
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia.
| | - Rocky Y Su
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Wee Han Lim
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - MengKe Feng
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | | | - Brandon Severin
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Department of Engineering Science, University of Oxford, Oxford, UK
| | - Will Gilbert
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Nard Dumoulin Stuyck
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Tuomo Tanttu
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Santiago Serrano
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Jesus D Cifuentes
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Ingvild Hansen
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Amanda E Seedhouse
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Ensar Vahapoglu
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Ross C C Leon
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Quantum Motion Technologies, London, UK
| | | | | | - Michael L W Thewalt
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Fay E Hudson
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Christopher C Escott
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Natalia Ares
- Department of Engineering Science, University of Oxford, Oxford, UK
| | - Stephen D Bartlett
- Centre for Engineered Quantum Systems, School of Physics, University of Sydney, Sydney, New South Wales, Australia
| | - Andrea Morello
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
| | - Andre Saraiva
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Arne Laucht
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia
- Diraq, Sydney, New South Wales, Australia
| | - Andrew S Dzurak
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia.
- Diraq, Sydney, New South Wales, Australia.
| | - Chih Hwan Yang
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales, Australia.
- Diraq, Sydney, New South Wales, Australia.
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2
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Jirovec D, Mutter PM, Hofmann A, Crippa A, Rychetsky M, Craig DL, Kukucka J, Martins F, Ballabio A, Ares N, Chrastina D, Isella G, Burkard G, Katsaros G. Dynamics of Hole Singlet-Triplet Qubits with Large g-Factor Differences. Phys Rev Lett 2022; 128:126803. [PMID: 35394319 DOI: 10.1103/physrevlett.128.126803] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 01/24/2022] [Accepted: 02/24/2022] [Indexed: 06/14/2023]
Abstract
The spin-orbit interaction permits to control the state of a spin qubit via electric fields. For holes it is particularly strong, allowing for fast all electrical qubit manipulation, and yet an in-depth understanding of this interaction in hole systems is missing. Here we investigate, experimentally and theoretically, the effect of the cubic Rashba spin-orbit interaction on the mixing of the spin states by studying singlet-triplet oscillations in a planar Ge hole double quantum dot. Landau-Zener sweeps at different magnetic field directions allow us to disentangle the effects of the spin-orbit induced spin-flip term from those caused by strongly site-dependent and anisotropic quantum dot g tensors. Our work, therefore, provides new insights into the hole spin-orbit interaction, necessary for optimizing future qubit experiments.
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Affiliation(s)
- Daniel Jirovec
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Philipp M Mutter
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - Andrea Hofmann
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Alessandro Crippa
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - Marek Rychetsky
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - David L Craig
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - Josip Kukucka
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Frederico Martins
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
- Hitachi Cambridge Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Andrea Ballabio
- L-NESS, Physics Department, Politecnico di Milano, via Anzani 42, 22100, Como, Italy
| | - Natalia Ares
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom
| | - Daniel Chrastina
- L-NESS, Physics Department, Politecnico di Milano, via Anzani 42, 22100, Como, Italy
| | - Giovanni Isella
- L-NESS, Physics Department, Politecnico di Milano, via Anzani 42, 22100, Como, Italy
| | - Guido Burkard
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - Georgios Katsaros
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
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3
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Moon H, Lennon DT, Kirkpatrick J, van Esbroeck NM, Camenzind LC, Yu L, Vigneau F, Zumbühl DM, Briggs GAD, Osborne MA, Sejdinovic D, Laird EA, Ares N. Machine learning enables completely automatic tuning of a quantum device faster than human experts. Nat Commun 2020; 11:4161. [PMID: 32814777 PMCID: PMC7438325 DOI: 10.1038/s41467-020-17835-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 07/16/2020] [Indexed: 11/28/2022] Open
Abstract
Variability is a problem for the scalability of semiconductor quantum devices. The parameter space is large, and the operating range is small. Our statistical tuning algorithm searches for specific electron transport features in gate-defined quantum dot devices with a gate voltage space of up to eight dimensions. Starting from the full range of each gate voltage, our machine learning algorithm can tune each device to optimal performance in a median time of under 70 minutes. This performance surpassed our best human benchmark (although both human and machine performance can be improved). The algorithm is approximately 180 times faster than an automated random search of the parameter space, and is suitable for different material systems and device architectures. Our results yield a quantitative measurement of device variability, from one device to another and after thermal cycling. Our machine learning algorithm can be extended to higher dimensions and other technologies.
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Affiliation(s)
- H Moon
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | - D T Lennon
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | | | - N M van Esbroeck
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven, MB, 5600, The Netherlands
| | - L C Camenzind
- Department of Physics, University of Basel, Basel, 4056, Switzerland
| | - Liuqi Yu
- Department of Physics, University of Basel, Basel, 4056, Switzerland
| | - F Vigneau
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | - D M Zumbühl
- Department of Physics, University of Basel, Basel, 4056, Switzerland
| | - G A D Briggs
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | - M A Osborne
- Department of Engineering, University of Oxford, Walton Well Road, Oxford, OX2 6ED, UK
| | - D Sejdinovic
- Department of Statistics, University of Oxford, 24-29 St Giles, Oxford, OX1 3LB, UK
| | - E A Laird
- Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK
| | - N Ares
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
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4
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Pearson AN, Khosla KE, Mergenthaler M, Briggs GAD, Laird EA, Ares N. Radio-frequency optomechanical characterization of a silicon nitride drum. Sci Rep 2020; 10:1654. [PMID: 32015416 PMCID: PMC6997228 DOI: 10.1038/s41598-020-58554-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Accepted: 01/13/2020] [Indexed: 11/09/2022] Open
Abstract
On-chip actuation and readout of mechanical motion is key to characterize mechanical resonators and exploit them for new applications. We capacitively couple a silicon nitride membrane to an off resonant radio-frequency cavity formed by a lumped element circuit. Despite a low cavity quality factor (QE ≈ 7.4) and off resonant, room temperature operation, we are able to parametrize several mechanical modes and estimate their optomechanical coupling strengths. This enables real-time measurements of the membrane's driven motion and fast characterization without requiring a superconducting cavity, thereby eliminating the need for cryogenic cooling. Finally, we observe optomechanically induced transparency and absorption, crucial for a number of applications including sensitive metrology, ground state cooling of mechanical motion and slowing of light.
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Affiliation(s)
- A N Pearson
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom
| | - K E Khosla
- Center for Engineered Quantum Systems, The School of Mathematics and Physics, The University of Queensland, St. Lucia, Queensland, 4072, Australia.,QOLS, Blackett Laboratory, Imperial College London, London, SW7 2AZ, United Kingdom
| | - M Mergenthaler
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom
| | - G A D Briggs
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom
| | - E A Laird
- Department of Physics, Lancaster University, Lancaster, LA1 4YB, United Kingdom
| | - N Ares
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom.
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5
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Abstract
A single-electron transistor embedded in a nanomechanical resonator represents an extreme limit of electron-phonon coupling. While it allows fast and sensitive electromechanical measurements, it also introduces backaction forces from electron tunnelling that randomly perturb the mechanical state. Despite the stochastic nature of this backaction, it has been predicted to create self-sustaining coherent mechanical oscillations under strong coupling conditions. Here, we verify this prediction using real-time measurements of a vibrating carbon nanotube transistor. This electromechanical oscillator has some similarities with a laser. The single-electron transistor pumped by an electrical bias acts as a gain medium and the resonator acts as a phonon cavity. Although the operating principle is unconventional because it does not involve stimulated emission, we confirm that the output is coherent. We demonstrate other analogues of laser behaviour, including injection locking, classical squeezing through anharmonicity, and frequency narrowing through feedback.
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Affiliation(s)
- Yutian Wen
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - N. Ares
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - F.J. Schupp
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - T. Pei
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - G.A.D. Briggs
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - E.A. Laird
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
- Department of Physics, Lancaster University, Lancaster, LA1 4YB, United Kingdom
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6
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Mergenthaler M, Liu J, Le Roy JJ, Ares N, Thompson AL, Bogani L, Luis F, Blundell SJ, Lancaster T, Ardavan A, Briggs GAD, Leek PJ, Laird EA. Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet. Phys Rev Lett 2017; 119:147701. [PMID: 29053322 DOI: 10.1103/physrevlett.119.147701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Indexed: 06/07/2023]
Abstract
Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.
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Affiliation(s)
- Matthias Mergenthaler
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Junjie Liu
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Jennifer J Le Roy
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Natalia Ares
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Amber L Thompson
- Chemical Crystallography, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Lapo Bogani
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Fernando Luis
- Instituto de Ciencia de Materiales de Aragón (CSIC-U. de Zaragoza), 50009 Zaragoza, Spain
| | - Stephen J Blundell
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Tom Lancaster
- Durham University, Centre for Materials Physics, Department of Physics, Durham DH1 3LE, United Kingdom
| | - Arzhang Ardavan
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - G Andrew D Briggs
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Peter J Leek
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Edward A Laird
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
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7
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Pei T, Pályi A, Mergenthaler M, Ares N, Mavalankar A, Warner JH, Briggs GAD, Laird EA. Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube. Phys Rev Lett 2017; 118:177701. [PMID: 28498696 DOI: 10.1103/physrevlett.118.177701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Indexed: 06/07/2023]
Abstract
The decay of spin-valley states is studied in a suspended carbon nanotube double quantum dot via the leakage current in Pauli blockade and via dephasing and decoherence of a qubit. From the magnetic field dependence of the leakage current, hyperfine and spin-orbit contributions to relaxation from blocked to unblocked states are identified and explained quantitatively by means of a simple model. The observed qubit dephasing rate is consistent with the hyperfine coupling strength extracted from this model and inconsistent with dephasing from charge noise. However, the qubit coherence time, although longer than previously achieved, is probably still limited by charge noise in the device.
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Affiliation(s)
- T Pei
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - A Pályi
- Department of Physics and MTA-BME Condensed Matter Research Group, Budapest University of Technology and Economics, 1111 Budapest, Hungary
| | - M Mergenthaler
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - N Ares
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - A Mavalankar
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - J H Warner
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - G A D Briggs
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - E A Laird
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
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8
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Ares N, Pei T, Mavalankar A, Mergenthaler M, Warner JH, Briggs GAD, Laird EA. Resonant Optomechanics with a Vibrating Carbon Nanotube and a Radio-Frequency Cavity. Phys Rev Lett 2016; 117:170801. [PMID: 27824476 DOI: 10.1103/physrevlett.117.170801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Indexed: 05/05/2023]
Abstract
In an optomechanical setup, the coupling between cavity and resonator can be increased by tuning them to the same frequency. We study this interaction between a carbon nanotube resonator and a radio-frequency tank circuit acting as a cavity. In this resonant regime, the vacuum optomechanical coupling is enhanced by the dc voltage coupling the cavity and the mechanical resonator. Using the cavity to detect the nanotube's motion, we observe and simulate interference between mechanical and electrical oscillations. We measure the mechanical ring down and show that further improvements to the system could enable the measurement of mechanical motion at the quantum limit.
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Affiliation(s)
- N Ares
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - T Pei
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - A Mavalankar
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - M Mergenthaler
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - J H Warner
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - G A D Briggs
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
| | - E A Laird
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
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9
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Ares N, Golovach VN, Katsaros G, Stoffel M, Fournel F, Glazman LI, Schmidt OG, De Franceschi S. Nature of tunable hole g factors in quantum dots. Phys Rev Lett 2013; 110:046602. [PMID: 25166183 DOI: 10.1103/physrevlett.110.046602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 10/12/2012] [Indexed: 05/27/2023]
Abstract
We report an electric-field-induced giant modulation of the hole g factor in SiGe nanocrystals. The observed effect is ascribed to a so-far overlooked contribution to the g factor that stems from the mixing between heavy- and light-hole wave functions. We show that the relative displacement between the confined heavy- and light-hole states, occurring upon application of the electric field, alters their mixing strength leading to a strong nonmonotonic modulation of the g factor.
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Affiliation(s)
- N Ares
- SPSMS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France
| | - V N Golovach
- SPSMS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France and Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany and IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain and Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 5, E-20018 San Sebastián, Spain
| | - G Katsaros
- SPSMS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France and Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany and Johannes Kepler University, Institute of Semiconductor and Solid State Physics, Altenbergerstrasse 69, 4040 Linz, Austria
| | - M Stoffel
- Université de Lorraine, Institut Jean Lamour, UMR CNRS 7198, Nancy-Université, BP 239, F-54506 Vandoeuvre-les-Nancy, France
| | - F Fournel
- CEA, LETI, MINATEC, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France
| | - L I Glazman
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
| | - O G Schmidt
- Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany
| | - S De Franceschi
- SPSMS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France
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10
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Katsaros G, Golovach VN, Spathis P, Ares N, Stoffel M, Fournel F, Schmidt OG, Glazman LI, De Franceschi S. Observation of spin-selective tunneling in SiGe nanocrystals. Phys Rev Lett 2011; 107:246601. [PMID: 22243017 DOI: 10.1103/physrevlett.107.246601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Indexed: 05/14/2023]
Abstract
Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band.
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Affiliation(s)
- G Katsaros
- SPSMS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France.
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11
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Abstract
The prediction of the response of a closed system to external perturbations is one of the central problems in quantum mechanics, and in this respect, the local density of states (LDOS) provides an in-depth description of such a response. The LDOS is the distribution of the overlaps squared connecting the set of eigenfunctions with the perturbed one. Here, we show that in the case of closed systems with classically chaotic dynamics, the LDOS is a Breit-Wigner distribution under very general perturbations of arbitrary high intensity. Consequently, we derive a semiclassical expression for the width of the LDOS which is shown to be very accurate for paradigmatic systems of quantum chaos. This Letter demonstrates the universal response of quantum systems with classically chaotic dynamics.
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Affiliation(s)
- Diego A Wisniacki
- Departamento de Física J. J. Giambiagi, FCEyN, UBA, and IFIBA, CONICET, Pabellón 1, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina
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12
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Abstract
Loschmidt echo (LE) is a measure of reversibility and sensitivity to perturbations of quantum evolutions. For weak perturbations its decay rate is given by the width of the local density of states (LDOS). When the perturbation is strong enough, it has been shown in chaotic systems that its decay is dictated by the classical Lyapunov exponent. However, several recent studies have shown an unexpected nonuniform decay rate as a function of the perturbation strength instead of that Lyapunov decay. Here we study the systematic behavior of this regime in perturbed cat maps. We show that some perturbations produce coherent oscillations in the width of LDOS that imprint clear signals of the perturbation in LE decay. We also show that if the perturbation acts in a small region of phase space (local perturbation) the effect is magnified and the decay is given by the width of the LDOS.
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Affiliation(s)
- Natalia Ares
- Departamento de Física J J Giambiagi, FCEN, UBA, Ciudad Universitaria, Buenos Aires, Argentina
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