| Budget Amount *help |
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 2005 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 2004 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 2003 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 2002 : ¥700,000 (Direct Cost : ¥700,000)
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| Research Abstract |
In this research project, the temporal evolution of quantum systems, especially that under the influence of the action of quantum measurements, has mainly been investigated.
As is well known, the temporal behavior of a quantum system is classified into three characteristic stages, i.e., the quadratic (Gaussian) behavior at short times, the exponential decay at intermediate times and the power decay at long times and on the basis of a solvable model, we first demonstrated these characteristics analytically.
Next, we have proposed a new scheme of driving a quantum system under investigation to a pure state irrespectively of its initial (in general mixed) state, by means of repeated measurements of another quantum system in interaction with the former. A remarkable feature of this method is that the two important notions in this kind of research work, that is, the fidelity and the yield, can be made compatible, the condition which is not easily implemented in many other attempts. Moreover, since its fundamental idea is so simple and general, it retains high flexibility and applicability and in fact, it has been generalized and applied to many different physical situations. Among such applications, purification of qubit systems, extraction of entangled states that can be spatially separated, construction of filters for more general quantum states with the help of dynamical quantum Zeno effects and an experimental proposal of this scheme in the quantum dot system are noted.
We have also investigated the master equation that usually describes a quantum system under the influence of its dissipative and decohering environment to clarify its mathematically subtle points so far somehow overlooked.
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