6,993 research outputs found
Directly Coupled Observers for Quantum Harmonic Oscillators with Discounted Mean Square Cost Functionals and Penalized Back-action
This paper is concerned with quantum harmonic oscillators consisting of a
quantum plant and a directly coupled coherent quantum observer. We employ
discounted quadratic performance criteria in the form of exponentially weighted
time averages of second-order moments of the system variables. A coherent
quantum filtering (CQF) problem is formulated as the minimization of the
discounted mean square of an estimation error, with which the dynamic variables
of the observer approximate those of the plant. The cost functional also
involves a quadratic penalty on the plant-observer coupling matrix in order to
mitigate the back-action of the observer on the covariance dynamics of the
plant. For the discounted mean square optimal CQF problem with penalized
back-action, we establish first-order necessary conditions of optimality in the
form of algebraic matrix equations. By using the Hamiltonian structure of the
Heisenberg dynamics and related Lie-algebraic techniques, we represent this set
of equations in a more explicit form in the case of equally dimensioned plant
and observer.Comment: 11 pages, a brief version to be submitted to the IEEE 2016 Conference
on Norbert Wiener in the 21st Century, 13-15 July, Melbourne, Australi
General relativistic effects in quantum interference of photons
Quantum mechanics and general relativity have been extensively and
independently confirmed in many experiments. However, the interplay of the two
theories has never been tested: all experiments that measured the influence of
gravity on quantum systems are consistent with non-relativistic, Newtonian
gravity. On the other hand, all tests of general relativity can be described
within the framework of classical physics. Here we discuss a quantum
interference experiment with single photons that can probe quantum mechanics in
curved space-time. We consider a single photon travelling in superposition
along two paths in an interferometer, with each arm experiencing a different
gravitational time dilation. If the difference in the time dilations is
comparable with the photon's coherence time, the visibility of the quantum
interference is predicted to drop, while for shorter time dilations the effect
of gravity will result only in a relative phase shift between the two arms. We
discuss what aspects of the interplay between quantum mechanics and general
relativity are probed in such experiments and analyze the experimental
feasibility.Comment: 16 pages, new appendix, published versio
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