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Reply to "Comment on `Reduced coherence in double-slit diffraction of neutrons'"
No full textWe reply to the comment by Sanz and Borondo [Phys. Rev. A 77, 057601 (2008)] on our paper [Tumulka et al., Phys. Rev. A 75, 055602 (2007)] concerning the double-slit diffraction experiment with neutrons published in Zeilinger et al. [Rev. Mod. Phys. 60, 1067 (1988)]. We argue in particular that Sanz and Borondo's new arguments for the presence of significant decoherence in that experiment are unconvincing
Reduced coherence in double-slit diffraction of neutrons
No full textIn diffraction experiments with particle beams, several effects lead to a fringe visibility reduction of the interference pattern. We theoretically describe the intensity one can measure in a double-slit setup and compare the results with the experimental data obtained with cold neutrons. Our conclusion is that for cold neutrons the fringe visibility reduction is due not to decoherence, but to initial incoherence
Bohmian Trajectories for Hamiltonians with Interior–Boundary Conditions
No full textRecently, there has been progress in developing interior–boundary conditions (IBCs) as a technique of avoiding the problem of ultraviolet divergence in non-relativistic quantum field theories while treating space as a continuum and electrons as point particles. An IBC can be expressed in the particle-position representation of a Fock vector ψ as a condition on the values of ψ on the set of collision configurations, and the corresponding Hamiltonian is defined on a domain of vectors satisfying this condition. We describe here how Bohmian mechanics can be extended to this type of Hamiltonian. In fact, part of the development of IBCs was inspired by the Bohmian picture. Particle creation and annihilation correspond to jumps in configuration space; the annihilation is deterministic and occurs when two particles (of the appropriate species) meet, whereas the creation is stochastic and occurs at a rate dictated by the demand for the equivariance of the | ψ| 2 distribution, time reversal symmetry, and the Markov property. The process is closely related to processes known as Bell-type quantum field theories
Canonical Typicality
No full textIt is well known that a system, S, weakly coupled to a heat bath, B, is described by the canonical ensemble when the composite, S+B, is described by the microcanonical ensemble corresponding to a suitable energy shell. This is true both for classical distributions on the phase space and for quantum density matrices. Here we show that a much stronger statement holds for quantum systems. Even if the state of the composite corresponds to a single wave function rather than a mixture, the reduced density matrix of the system is canonical, for the overwhelming majority of wave functions in the subspace corresponding to the energy interval encompassed by the microcanonical ensemble. This clarifies, expands and justifies remarks made by Schroedinger in 1952
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