Critical dynamics of decoherence
(Submitted on 30 Nov 2009)
The quantum-classical border Niels Bohr postulated to account for the definiteness of measurement outcomes is explained by decoherence. Decoherence, as a destroyer of quantum coherence and entanglement, is also a respected foe in novel applications of quantum physics (such as quantum computing or quantum metrology). So far, studies of decoherence focused on systems prepared typically in a Schroedinger cat-like superposition, and then instantaneously coupled to an otherwise static environment. We study decoherence induced by many-body dynamic environment undergoing a non-equilibrium (quantum) phase transition. As environment "monitors" the quantum system, its sensitivity -- and, consequently, efficiency of decoherence -- is amplified by a phase transition, as is often the case in the real world detectors (bubble chambers, photographic emulsions, or rhodopsin in our eyes). We show that decoherence happens almost exclusively as the critical point of the environment is traversed, and is significantly enhanced by its non-equilibrium phase transition dynamics. Our calculation yields a simple expression that relates decoherence to the universal critical exponents in a way that parallels theory of topological defect creation in non-equilibrium phase transitions.