Reversible quantum measurement with arbitrary spins

We propose a physically reversible quantum measurement of an arbitrary spin-s system using a spin-j probe with a simple interaction. By the physical reversibility, the measurement has a reversing measurement, which can restore the premeasurement state from the postmeasurement state with a nonzero probability of success. In the case of a spin-1/2 system (s = 1/2), we explicitly construct such a reversing measurement and evaluate the degree of reversibility in terms of fidelity to give a criterion for the successful recovery of the measured state. When the probe has a high spin (j > 1/2), the fidelity changes drastically during both the reversible and reversing measurements. The higher spin probe thus makes the recovery of the quantum state more conspicuous, albeit with a lower probability of success. When the spin of the system is high (s > 1/2), we show that the reversing measurement for a spin-1/2 system can serve as an approximate reversing measurement for a high-spin system in two physical situations: one in which the measured system is initially in a two-dimensional subspace and the other in which the interaction is sufficiently weak. In particular, in the latter case, even a cat state can be recovered almost deterministically in spite of a large change in fidelity. PACS: 03.65.Ta, 03.67.-a