2018 Fiscal Year Annual Research Report
Quantum langevin equation method in non-Markovian dynamics
| Project/Area Number |
17F17821
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
NORI FRANCO 国立研究開発法人理化学研究所, 開拓研究本部, 主任研究員 (50415262)
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| Co-Investigator(Kenkyū-buntansha) |
ZHOU ZHENG-YANG 国立研究開発法人理化学研究所, 開拓研究本部, 外国人特別研究員
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| Project Period (FY) |
2017-11-10 – 2020-03-31
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| Keywords | open quantum systems / bath information / harmonic oscillators / thermal equilibrium |
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| Outline of Annual Research Achievements |
In the fiscal year 2018, my research focus on the open quantum systems method and its application.
We have developed a stochastic c-number Langevin equation method for open quantum systems. This method can conveniently access both system information and bath information in systems coupled to bosonic bath. Therefore, it can be a good tool for the studies in quantum thermodynamics and quantum information. I have also discussed with several researchers in the field of open quantum systems to improve this work and find potential problems. The manuscript is nearly finished and will be submitted soon.
I began to study the thermodynamic properties of the coupled harmonic oscillator systems. This is a very simple model but related to many thermal effects in the classical limit. The concerned problems are mainly focused on the conditions for two oscillator clusters to reach classical thermal equilibrium. Some preliminary results have been got. Now, I am discussing with the cooperators to get a better understanding of this project.
I have cooperations with researchers in the field of quantum information. We have proposed a way to reduce decoherence in multi-qubit systems by optimal permutation. The decoherence effects of the bath is calculated by the quantum Langevin equation method. We also have several other ongoing works studying more realistic situations.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As was planned in the initial proposal, the focus of the first year will be the open system method. The hierarchy method for the nonlinear coupling was finished in later FY2017, though no novel results were found. I started a work about steady state of two-level system in FY2017, but found it problematic. However, this failure had no significant influence because the related project was not included in the first-year plan. The development of stochastic method met some technical problems at first, but the main part was finished in the early FY2018. Therefore, the target of the first year is achieved on time. In the later FY 2018, I switched to the plan of the second year of this two-year research project. A project about the thermal equilibrium of harmonic oscillators was started. However, the progress was delayed due to some critical comments on some technical aspects of the work about the stochastic method. Several months were spent to clarify the validity and the novelty of our work. Now, I have persuaded the other researchers and can come back to the plan. I have also cooperated with researchers in quantum information. Our methods are found to be effective in describing the decoherence and control effects in muti-qubit systems. Overall, the research progress is consistent with the plan.
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| Strategy for Future Research Activity |
In FY2019, I plan to proceed on two directions. First, I will continue the study of the thermodynamic properties of quantum systems from a dynamical way, which is part of the original proposal. After completing the stochastic c-number Langevin equation, it is possible to access much information of different quantum systems. Therefore, in addition to harmonic oscillators, we can study the atoms or the quantum dots, which can have richer thermodynamic behavior. Recently, non-Hermitian systems have attracted much interest, so I plan to study the dynamics and thermodynamic properties of such systems. Second, I will keep cooperating with researchers in the field of quantum information. The present work considers the decoherence in a system of four qubits. We plan to study larger systems which are more realistic for quantum computation. For multi-qubit systems, the simulation of the bath is difficult and faces challenges similar to the ones in thermodynamics. Therefore, these studies can be done together with the project in quantum thermodynamics. In addition, I will also explore some applications of our method in quantum optics.
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