表題番号：2016B-173
日付：2017/02/27

研究課題量子ダイナミクスの新展開

研究者所属（当時） | 資格 | 氏名 | |
---|---|---|---|

（代表者） | 理工学術院 先進理工学部 | 教授 | 中里 弘道 |

- 研究成果概要
- In this project, I have examined quantum dynamics of some systems from unique perspectives.

First, our recent proposal of how to construct solvable quantum models for time-dependent two-level systems has been applied to a pair of two-level systems interacting to each other under external time-dependent magnetic fields. The system is modeled by a general Hamiltonian endowed with a symmetry that enables one to reduce the total dynamics into two independent two-dimensional subdynamics. Each of the subdynamics is shown to be brought into an exactly solvable form by appropriately engineering the magnetic fields and thus we obtain an exact time evolution of the compound system. Several physically relevant and interesting quantities are evaluated exactly to disclose intriguing phenomena in such a system.

On the other hand, it has recently been shown that a strong-amplitude-damping process applied locally on a part of a quantum system can have a beneficial effect on the dynamics of the remaining part of the system. Quantum operations that cannot be implemented without the dissipation become achievable by the action of the strong dissipative process. Here we generalize this idea by identifying decoherence-free subspaces (DFSs) as the subspaces in which the dynamics becomes more complex. We characterize the set of reachable operations within the DFSs. We provide three examples that become fully controllable within the DFSs while the control over the original Hilbert space in the absence of dissipation is trivial. In particular, we show that the (classical) Ising Hamiltonian is turned into a Heisenberg Hamiltonian by strong collective decoherence, which provides universal quantum computation within the DFSs.