Consistent Histories Approach to the Unruh Effect

C. H. Woo

Duncan Noltingk

Using the HPO approach to consistent histories we re-derive Unruh's result that an observer constantly accelerating through the Minkowski vacuum appears to be immersed in a thermal bath. We show that propositions about any symmetry of the system always form a consistent set and that the probabilities associated with such propositions are decided by their value in the initial state. We use this fact to postulate a condition on the decoherence functional in the HPO set-up. Finally we show that the Unruh effect arises from the fact that the initial density matrix corresponding to the inertial vacuum can be written as a thermal density matrix in the Fock basis associated with the accelerating observer.

Claus Kiefer

Claus Kiefer

Jürgen Audretsch, Michael B. Mensky, Rainer Müller

We consider the influence of continuous decoherence on the excitation of an accelerated detector, an effect which must be taken into account in physically realistic realizations of the Unruh effect. As a model we use a quantum two-level system (as the detector) coupled to a massless scalar quantum field. This composite quantum system is treated as an open system which interacts with an environment so that continuous decoherence results. We develop a formalism that models the interaction with an environment approximately as a continuous measurement, represented by a sequence of state reductions. This leads to a description in terms of ``histories'' of the detector. Evolution operators corresponding to different histories of the detector can then be considered separately. The density matrix for the mixed state which results after a sequence of nonselective measurements is worked out explicitly. Based on the same formalism, it is also possible to correlate the time of the transition of the detector with the trajectories of the Minkowski particles which are emitted during this process, thus localizing the space-time region where they are created.

Danko Dimchev Georgiev

We discuss the origin of quantum complementarity using Feynman's sum-over-histories approach to Quantum Mechanics (QM). We analyze two experimental setups introduced by W. G. Unruh and S. Afshar and show how one should consistently calculate the existence of which-way information using interfering quantum histories. Then we discuss the possible problems associated with the notion of which way information and provide an explanation why Englert-Greenberger duality relation cannot be violated experimentally if the standard QM postulates are accepted.