Abstracts
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Relativistic Quantum Metrology
Jim van Meter, National Institute of Standards and Technology
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Utilizing a generally covariant formalism developed by Brunetti, Fredenhagen, and Verch for handling quantum fields in a locally perturbed, classical spacetime background, Downes, Milburn, and Caves recently introduced the idea of applying the Cramer-Rao bound to optimizing gravitational parameter estimation. This results in a Heisenberg-like uncertainty relation between quantum field observables and classical gravitational quantities. Building on their work I show how this general method can be adapted to global spacetime parameters and discuss various applications, from cosmological observations to gravimeters to accelerometers. In particular, I derive a bound on the accuracy of laser-interferometric gravitational wave observatories.
Distributed Management of Density Matrices
Rodney Van Meter, Keio University
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The density matrix (d.m.) of a quantum state is a statistical construct, describing our best understanding of the actual state based on our prior experience with, and constant monitoring of, the experimental apparatus and its ability to store and manipulate quantum states. An operational problem arises when a multi-particle state is held in physically distributed locations and each node must make real-time decisions on the disposition of the quantum state, as in a quantum repeater network. Each node holding part of the state may independently choose to manipulate the state, affecting its fidelity. Software systems must concern themselves with the discrepancy between (in a two-party state) Alice's notion of the d.m., Bob's notion of the d.m., and the d.m. that would be compiled by an observer Orville not subject to relativistic constraints on information. We have developed a set of principles for guiding the implementation, and compare four methods for meeting the constraints: by contract, by centralized control, by distributed calculation and decision, and by direct monitoring. Simulations including direct monitoring will be presented.