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Stilck França D, Markovich LA, Dobrovitski VV, Werner AH, Borregaard J. Efficient and robust estimation of many-qubit Hamiltonians. Nat Commun 2024; 15:311. [PMID: 38191453 PMCID: PMC10774346 DOI: 10.1038/s41467-023-44012-5] [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] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Accepted: 11/24/2023] [Indexed: 01/10/2024] Open
Abstract
Characterizing the interactions and dynamics of quantum mechanical systems is an essential task in developing quantum technologies. We propose an efficient protocol based on the estimation of the time-derivatives of few qubit observables using polynomial interpolation for characterizing the underlying Hamiltonian dynamics and Markovian noise of a multi-qubit device. For finite range dynamics, our protocol exponentially relaxes the necessary time-resolution of the measurements and quadratically reduces the overall sample complexity compared to previous approaches. Furthermore, we show that our protocol can characterize the dynamics of systems with algebraically decaying interactions. The implementation of the protocol requires only the preparation of product states and single-qubit measurements. Furthermore, we improve a shadow tomography method for quantum channels that is of independent interest and discuss the robustness of the protocol to various errors. This protocol can be used to parallelize the learning of the Hamiltonian, rendering it applicable for the characterization of both current and future quantum devices.
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Affiliation(s)
- Daniel Stilck França
- QMATH, Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark.
- Univ Lyon, ENS Lyon, UCBL, CNRS, Inria, LIP, F-69342, Lyon, Cedex 07, France.
| | - Liubov A Markovich
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628 CJ, The Netherlands
- Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, Leiden, 2300 RA, The Netherlands
| | - V V Dobrovitski
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628 CJ, The Netherlands
| | - Albert H Werner
- QMATH, Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
- NBIA, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100, Copenhagen, Denmark
| | - Johannes Borregaard
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628 CJ, The Netherlands
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
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2
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Baier S, Bradley CE, Middelburg T, Dobrovitski VV, Taminiau TH, Hanson R. Orbital and Spin Dynamics of Single Neutrally-Charged Nitrogen-Vacancy Centers in Diamond. Phys Rev Lett 2020; 125:193601. [PMID: 33216607 DOI: 10.1103/physrevlett.125.193601] [Citation(s) in RCA: 4] [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: 07/30/2020] [Accepted: 10/02/2020] [Indexed: 06/11/2023]
Abstract
The neutral charge state plays an important role in quantum information and sensing applications based on nitrogen-vacancy centers. However, the orbital and spin dynamics remain unexplored. Here, we use resonant excitation of single centers to directly reveal the fine structure, enabling selective addressing of spin-orbit states. Through pump-probe experiments, we find the orbital relaxation time (430 ns at 4.7 K) and measure its temperature dependence up to 11.8 K. Finally, we reveal the spin relaxation time (1.5 s) and realize projective high-fidelity single-shot readout of the spin state (≥98%).
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Affiliation(s)
- S Baier
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
| | - C E Bradley
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
| | - T Middelburg
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
| | - V V Dobrovitski
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
| | - T H Taminiau
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
| | - R Hanson
- QuTech, Delft University of Technology, 2628 CJ Delft, Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, Netherlands
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3
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Petit L, Boter JM, Eenink HGJ, Droulers G, Tagliaferri MLV, Li R, Franke DP, Singh KJ, Clarke JS, Schouten RN, Dobrovitski VV, Vandersypen LMK, Veldhorst M. Spin Lifetime and Charge Noise in Hot Silicon Quantum Dot Qubits. Phys Rev Lett 2018; 121:076801. [PMID: 30169086 DOI: 10.1103/physrevlett.121.076801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Indexed: 06/08/2023]
Abstract
We investigate the magnetic field and temperature dependence of the single-electron spin lifetime in silicon quantum dots and find a lifetime of 2.8 ms at a temperature of 1.1 K. We develop a model based on spin-valley mixing and find that Johnson noise and two-phonon processes limit relaxation at low and high temperature, respectively. We also investigate the effect of temperature on charge noise and find a linear dependence up to 4 K. These results contribute to the understanding of relaxation in silicon quantum dots and are promising for qubit operation at elevated temperatures.
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Affiliation(s)
- L Petit
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - J M Boter
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - H G J Eenink
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - G Droulers
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - M L V Tagliaferri
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - R Li
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - D P Franke
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - K J Singh
- Components Research, Intel Corporation, 2501 NE Century Blvd, Hillsboro, Oregon 97124, USA
| | - J S Clarke
- Components Research, Intel Corporation, 2501 NE Century Blvd, Hillsboro, Oregon 97124, USA
| | - R N Schouten
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - V V Dobrovitski
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - L M K Vandersypen
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - M Veldhorst
- QuTech and Kavli Institute of Nanoscience, TU Delft, P.O. Box 5046, 2600 GA Delft, Netherlands
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Fotso HF, Feiguin AE, Awschalom DD, Dobrovitski VV. Suppressing Spectral Diffusion of Emitted Photons with Optical Pulses. Phys Rev Lett 2016; 116:033603. [PMID: 26849596 DOI: 10.1103/physrevlett.116.033603] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Indexed: 06/05/2023]
Abstract
In many quantum architectures the solid-state qubits, such as quantum dots or color centers, are interfaced via emitted photons. However, the frequency of photons emitted by solid-state systems exhibits slow uncontrollable fluctuations over time (spectral diffusion), creating a serious problem for implementation of the photon-mediated protocols. Here we show that a sequence of optical pulses applied to the solid-state emitter can stabilize the emission line at the desired frequency. We demonstrate efficiency, robustness, and feasibility of the method analytically and numerically. Taking nitrogen-vacancy center in diamond as an example, we show that only several pulses, with the width of 1 ns, separated by few ns (which is not difficult to achieve) can suppress spectral diffusion. Our method provides a simple and robust way to greatly improve the efficiency of photon-mediated entanglement and/or coupling to photonic cavities for solid-state qubits.
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Affiliation(s)
- H F Fotso
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - A E Feiguin
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - D D Awschalom
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
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Taminiau TH, Cramer J, van der Sar T, Dobrovitski VV, Hanson R. Universal control and error correction in multi-qubit spin registers in diamond. Nat Nanotechnol 2014; 9:171-6. [PMID: 24487650 DOI: 10.1038/nnano.2014.2] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Accepted: 01/07/2014] [Indexed: 05/05/2023]
Abstract
Quantum registers of nuclear spins coupled to electron spins of individual solid-state defects are a promising platform for quantum information processing. Pioneering experiments selected defects with favourably located nuclear spins with particularly strong hyperfine couplings. To progress towards large-scale applications, larger and deterministically available nuclear registers are highly desirable. Here, we realize universal control over multi-qubit spin registers by harnessing abundant weakly coupled nuclear spins. We use the electron spin of a nitrogen-vacancy centre in diamond to selectively initialize, control and read out carbon-13 spins in the surrounding spin bath and construct high-fidelity single- and two-qubit gates. We exploit these new capabilities to implement a three-qubit quantum-error-correction protocol and demonstrate the robustness of the encoded state against applied errors. These results transform weakly coupled nuclear spins from a source of decoherence into a reliable resource, paving the way towards extended quantum networks and surface-code quantum computing based on multi-qubit nodes.
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Affiliation(s)
- T H Taminiau
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - J Cramer
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - T van der Sar
- 1] Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands [2]
| | - V V Dobrovitski
- Ames Laboratory and Iowa State University, Ames, Iowa 50011, USA
| | - R Hanson
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
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6
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Taminiau TH, Wagenaar JJT, van der Sar T, Jelezko F, Dobrovitski VV, Hanson R. Detection and control of individual nuclear spins using a weakly coupled electron spin. Phys Rev Lett 2012; 109:137602. [PMID: 23030119 DOI: 10.1103/physrevlett.109.137602] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Indexed: 06/01/2023]
Abstract
We experimentally isolate, characterize, and coherently control up to six individual nuclear spins that are weakly coupled to an electron spin in diamond. Our method employs multipulse sequences on the electron spin that resonantly amplify the interaction with a selected nuclear spin and at the same time dynamically suppress decoherence caused by the rest of the spin bath. We are able to address nuclear spins with interaction strengths that are an order of magnitude smaller than the electron spin dephasing rate. Our results provide a route towards tomography with single-nuclear-spin sensitivity and greatly extend the number of available quantum bits for quantum information processing in diamond.
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Affiliation(s)
- T H Taminiau
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, Netherlands
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7
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Fuchs GD, Falk AL, Dobrovitski VV, Awschalom DD. Spin coherence during optical excitation of a single nitrogen-vacancy center in diamond. Phys Rev Lett 2012; 108:157602. [PMID: 22587283 DOI: 10.1103/physrevlett.108.157602] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 01/07/2012] [Indexed: 05/31/2023]
Abstract
We examine the quantum spin state of a single nitrogen-vacancy (NV) center in diamond at room temperature as it makes a transition from the orbital ground state (GS) to the orbital excited state (ES) during nonresonant optical excitation. While the fluorescence readout of NV-center spins relies on conservation of the longitudinal spin projection during optical excitation, the question of quantum phase preservation has not been examined. Using Ramsey measurements and quantum process tomography of the optical excitation process, we measure a trace fidelity of F=0.87±0.03, which includes ES spin dephasing during measurement. Extrapolation to the moment of optical excitation yields F≈0.95. This result provides insight into the interaction between spin coherence and nonresonant optical absorption through a vibronic sideband.
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Affiliation(s)
- G D Fuchs
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA
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Abstract
We experimentally demonstrate single-spin magnetometry with multipulse sensing sequences. The use of multipulse sequences can greatly increase the sensing time per measurement shot, resulting in enhanced ac magnetic field sensitivity. We theoretically derive and experimentally verify the optimal number of sensing cycles, for which the effects of decoherence and increased sensing time are balanced. We perform these experiments for oscillating magnetic fields with fixed phase as well as for fields with random phase. Finally, by varying the phase and frequency of the ac magnetic field, we measure the full frequency-filtering characteristics of different multipulse schemes and discuss their use in magnetometry applications.
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Affiliation(s)
- G de Lange
- Kavli Institute of Nanoscience Delft, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
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9
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de Lange G, Wang ZH, Riste D, Dobrovitski VV, Hanson R. Universal Dynamical Decoupling of a Single Solid-State Spin from a Spin Bath. Science 2010; 330:60-3. [DOI: 10.1126/science.1192739] [Citation(s) in RCA: 529] [Impact Index Per Article: 37.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Dobrovitski VV, de Lange G, Ristè D, Hanson R. Bootstrap tomography of the pulses for quantum control. Phys Rev Lett 2010; 105:077601. [PMID: 20868076 DOI: 10.1103/physrevlett.105.077601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2010] [Revised: 07/16/2010] [Indexed: 05/29/2023]
Abstract
Long-time dynamical decoupling and quantum control of qubits require high-precision control pulses. Full characterization (quantum tomography) of imperfect pulses presents a bootstrap problem: tomography requires initial states of a qubit which cannot be prepared without perfect pulses. We present a protocol for pulse error analysis, specifically tailored for a wide range of the single solid-state electron spins. Using a single electron spin of a nitrogen-vacancy center in diamond, we experimentally verify the correctness of the protocol, and demonstrate its usefulness for quantum control tasks.
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Affiliation(s)
- V V Dobrovitski
- Ames Laboratory, U.S. DOE, Iowa State University, Ames Iowa 50011, USA
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11
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Abstract
Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. By calibrating the spin rotation with an adiabatic passage, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. With an adiabatic passage to calibrate the spin rotation, we observed dynamics on sub-nanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin.
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Affiliation(s)
- G D Fuchs
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, CA 93106, USA
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12
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Dobrovitski VV, Feiguin AE, Hanson R, Awschalom DD. Decay of Rabi oscillations by dipolar-coupled dynamical spin environments. Phys Rev Lett 2009; 102:237601. [PMID: 19658973 DOI: 10.1103/physrevlett.102.237601] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Indexed: 05/28/2023]
Abstract
We study the Rabi oscillations decay of a spin decohered by a spin bath whose internal dynamics is caused by dipolar coupling between the bath spins. The form and rate of decay as a function of the intrabath coupling is obtained analytically, and confirmed numerically. The complex form of decay smoothly varies from power law to exponential, and the rate changes nonmonotonically with the intrabath coupling, decreasing for both slow and fast baths. The form and rate of Rabi oscillations decay can be used to experimentally determine the intrabath coupling strength for a broad class of solid-state systems.
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Affiliation(s)
- V V Dobrovitski
- Ames Laboratory U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
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Fuchs GD, Dobrovitski VV, Hanson R, Batra A, Weis CD, Schenkel T, Awschalom DD. Excited-state spectroscopy using single spin manipulation in diamond. Phys Rev Lett 2008; 101:117601. [PMID: 18851332 DOI: 10.1103/physrevlett.101.117601] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Indexed: 05/26/2023]
Abstract
We use single-spin resonant spectroscopy to study the spin structure in the orbital excited state of a diamond nitrogen-vacancy (N-V) center at room temperature. The data show that the excited-state spin levels have a zero-field splitting that is approximately half of the value of the ground state levels, a g factor similar to the ground state value, and a hyperfine splitting approximately 20x larger than in the ground state. In addition, the width of the resonances reflects the electronic lifetime in the excited state. We also show that the spin level splitting can significantly differ between N-V centers, likely due to the effects of local strain, which provides a pathway to control over the spin Hamiltonian and may be useful for quantum-information processing.
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Affiliation(s)
- G D Fuchs
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA
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Affiliation(s)
- R. Hanson
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
- Ames Laboratory and Iowa State University, Ames, IA 50011, USA
| | - V. V. Dobrovitski
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
- Ames Laboratory and Iowa State University, Ames, IA 50011, USA
| | - A. E. Feiguin
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
- Ames Laboratory and Iowa State University, Ames, IA 50011, USA
| | - O. Gywat
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
- Ames Laboratory and Iowa State University, Ames, IA 50011, USA
| | - D. D. Awschalom
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
- Ames Laboratory and Iowa State University, Ames, IA 50011, USA
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Al-Hassanieh KA, Dobrovitski VV, Dagotto E, Harmon BN. Numerical modeling of the central spin problem using the spin-coherent-state representation. Phys Rev Lett 2006; 97:037204. [PMID: 16907541 DOI: 10.1103/physrevlett.97.037204] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2005] [Indexed: 05/11/2023]
Abstract
In this work, we consider decoherence of a central spin by a spin bath. In order to study the nonperturbative decoherence regimes, we develop an efficient mean-field-based method for modeling the spin-bath decoherence, based on the representation of the central spin density matrix. The method can be applied to longitudinal and transverse relaxation at different external fields. In particular, by modeling large-size quantum systems (up to 16 000 bath spins), we make controlled predictions for the slow long-time decoherence of the central spin.
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Affiliation(s)
- K A Al-Hassanieh
- Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37996, USA
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Lages J, Dobrovitski VV, Katsnelson MI, De Raedt HA, Harmon BN. Decoherence by a chaotic many-spin bath. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:026225. [PMID: 16196702 DOI: 10.1103/physreve.72.026225] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Revised: 03/09/2005] [Indexed: 05/04/2023]
Abstract
We numerically investigate decoherence of a two-spin system (central system) by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical regime of the bath has been varied from quantum chaos to regular, while all other dynamical characteristics have been kept practically intact. We explicitly demonstrate that for a many-body quantum bath, the onset of quantum chaos leads to significantly faster and stronger decoherence compared to an equivalent non-chaotic bath. Moreover, the non-diagonal elements of the system's density matrix, the linear entropy, and the fidelity of the central system decay differently for chaotic and non-chaotic baths. Therefore, knowledge of the basic parameters of the bath (strength of the system-bath interaction, and the bath's spectral density of states) is not always sufficient, and much finer details of the bath's dynamics can strongly affect the decoherence process.
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Affiliation(s)
- J Lages
- Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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Dobrovitski VV, De Raedt HA, Katsnelson MI, Harmon BN. Quantum oscillations without quantum coherence. Phys Rev Lett 2003; 90:210401. [PMID: 12786540 DOI: 10.1103/physrevlett.90.210401] [Citation(s) in RCA: 7] [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: 12/08/2001] [Indexed: 05/24/2023]
Abstract
We study numerically the damping of quantum oscillations and the dynamics of the density matrix in model many-spin systems decohered by a spin bath. We show that oscillations of some density matrix elements can persist with considerable amplitude long after other elements, along with the entropy, have come close to saturation, i.e., when the system has been decohered almost completely. The oscillations exhibit very slow decay, and may be observable in experiments.
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Affiliation(s)
- V V Dobrovitski
- Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
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18
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Dobrovitski VV, De Raedt HA. Efficient scheme for numerical simulations of the spin-bath decoherence. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 67:056702. [PMID: 12786317 DOI: 10.1103/physreve.67.056702] [Citation(s) in RCA: 9] [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: 10/03/2002] [Revised: 01/22/2003] [Indexed: 05/24/2023]
Abstract
We demonstrate that the Chebyshev expansion method is a very efficient numerical tool for studying spin-bath decoherence of quantum systems. We consider two typical problems arising in studying decoherence of quantum systems consisting of a few coupled spins: (i) determining the pointer states of the system and (ii) determining the temporal decay of quantum oscillations. As our results demonstrate, for determining the pointer states, the Chebyshev-based scheme is at least a factor of 8 faster than existing algorithms based on the Suzuki-Trotter decomposition. For problems of the second type, the Chebyshev-based approach is 3-4 times faster than the Suzuki-Trotter-based schemes. This conclusion holds qualitatively for a wide spectrum of systems, with different spin baths and different Hamiltonians.
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Dobrovitski VV, Katsnelson MI, Harmon BN. Length scale coupling for nonlinear dynamical problems in magnetism. Phys Rev Lett 2003; 90:067201. [PMID: 12633322 DOI: 10.1103/physrevlett.90.067201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2001] [Indexed: 05/24/2023]
Abstract
The dynamics of real magnets is often governed by several interacting processes taking place simultaneously at different length scales. For dynamical simulations, the relevant length scales should be coupled, and the energy transfer accurately described. We show that in this case the micromagnetic theory is not always reliable. We present a coarse-graining approach applicable to nonlinear problems, which provides a unified description of all relevant length scales, allowing a smooth, seamless coupling. The simulations performed on model systems show that the coarse-graining approach achieves nearly the precision of all-atom simulations.
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Affiliation(s)
- V V Dobrovitski
- Ames Laboratory, Iowa State University, Ames, Iowa, 50011, USA
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Dobrovitski VV, Katsnelson MI, Harmon BN. Mechanisms of decoherence in weakly anisotropic molecular magnets. Phys Rev Lett 2000; 84:3458-3461. [PMID: 11019114 DOI: 10.1103/physrevlett.84.3458] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/1999] [Indexed: 05/23/2023]
Abstract
Decoherence mechanisms in crystals of weakly anisotropic magnetic molecules, such as V15, are studied. We show that an important decohering factor is the rapid thermal fluctuation of dipolar interactions between magnetic molecules. A model is proposed to describe the influence of this source of decoherence. Based on the exact solution of this model, we show that at relatively high temperatures, about 0.5 K, the quantum coherence in a V15 molecule is not suppressed and, in principle, can be detected experimentally. Therefore, these molecules may be suitable prototype systems for study of physical processes taking place in quantum computers.
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Affiliation(s)
- VV Dobrovitski
- Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
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