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Journal of Physics Conference Series

Purification through Zeno-like measurements: Variety of projective measurements

Makoto Unoki

Published Mar 21, 2006• 0 citations
Publisher

Abstract

We investigate an extension of a scheme for purification of quantum states called purification through Zeno-like measurements. In original scheme one repeatedly performs an identical projective measurement, we extend this scheme to the case that measured states are not identical at each time.
DOI
10.1088/1742-6596/31/1/065

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Measurements in quantum mechanics can not only effectively freeze the quantum system (the quantum Zeno effect) but also accelerate the time evolution of the system (the quantum anti-Zeno effect). In studies of these effects, a quantum state is prepared repeatedly by projecting the quantum state onto the initial state. In this paper, we repeatedly prepare the initial quantum state in a different manner. Instead of only performing projective measurements, we allow unitary operations to be performed, on a very short time-scale, after each measurement. We can then repeatedly prepare the initial state by performing some projective measurement and then, after each measurement, we perform a suitable unitary operation to end up with the same initial state as before. Our objective is to find the projective measurements that minimize the effective decay rate of the quantum state. We find such optimal measurements and the corresponding decay rates for a variety of system-environment models such as the pure dephasing model and the spin-boson model. We find that there can be considerable differences between this optimized effective decay rate and the usual decay rate obtained by repeatedly projecting onto the initial state. In particular, the Zeno and anti-Zeno regimes can be considerably modified.