Professor Shmuel Gurvitz

Weizmann Institute of Science, Israel

Abstract: The influence of the environment on a quantum system is mainly attributed to decoherence (dephasing), which destroys information, stored in the quantum system. However, the information is not totally lost but is hidden in the environment. It can be retrieved by a detector monitoring the environment. We investigate how such an information retrieval could influence decoherence of the quantum system. This is an issue of crucial importance in quantum cryptography, which relies on an assumption that one cannot make a measurement without perturbing the system. We demonstrate that this assumption is not always valid: one can gain information regarding the quantum system without increasing its decoherence rate, or even diminishing it. Besides its relevance for quantum cryptography, this result can be important for understanding quantum measurement and a role of information in quantum mechanics. A possible experimental realization is discussed.