2007 Fiscal Year Final Research Report Summary
Measurement/Decoherence-assisted quantum control theory
| Project/Area Number |
17550019
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | Keio University |
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Principal Investigator |
SUGAWARA Michihiko Keio University, Faculty of Science and Technology, Assistant Professor (40276415)
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| Project Period (FY) |
2005 – 2007
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| Keywords | chemical physics / quantum control / quantum measurement / decoherence / laser |
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| Research Abstract |
Coherent control scheme using lasers is known as an efficient quantum dynamics control method. In this work, we have developed an alternative control scheme utilizing decoherence process, which is introduced by the measurement onto quantum system, together with intense laser fields. It is widely known that frequent quantum measurements can hinder or prohibit the coherent dynamics driven by the laser field, such as Rabi oscillation in two-level system. We regard the quantum measurement as an input for controlling the system and theoretically investigate how efficiently the decoherence process can be utilized in the context of quantum dynamics control. In the present work, we accept the Neumann projection postulate, i. e., a measurement process on a quantum system with respect to a certain observable can be regarded as an elimination of off-diagonal elements of the system density matrix, or so called decoherence. In the limit of continuous measurement, the process can be effectively taken into account by introducing a dephasing operator in the Liouville equation, which governs the quantum system dynamics. We have applied the theory to the population control problem of L-type three level system and Kobrac-Rice type five level system under the stationary laser fields. We have also developed a new quantum control scheme of a general multi-level system. In this scheme, the system is decomposed into two independent sub-spaces by irradiating intense CW-lasers and well- established control schemes are applied onto the isolated small-space, which consists of only 2 or 3 levels.
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