Abstracts

Quantum channel parameter estimation with noisy initial states

Presenting Author: David Collins, Colorado Mesa University
Contributing Author(s): Jaimie Stephens, University of New Mexico

Quantum channel parameter estimation considers how to use physical resources to construct procedures for estimating parameters associated with an evolution process or channel of known type. Using the quantum Fisher information per channel invocation as a measure of the estimation accuracy, searching for an optimal estimation protocol reduces to finding optimal initial states for the physical system in use. In general, pure initial states are optimal: for the bit flip channel these are single qubit pure states and for the qubit depolarizing channel these are pairs of entangled qubits. We ask whether these results, particularly those involving entanglement or other quantum correlations, persist when pure initial states are unavailable, such as in nuclear magnetic resonance (NMR). We consider bit-flip and qubit depolarizing channel parameter estimation when the initial states are mixed. We compare protocols that use qubits in product states to a protocol that uses multiple qubits in a correlated state. We show that, for certain parameter values and initial state purities, the correlated state protocol provides a greater accuracy than the product state protocol. We show that, when comparing protocols using mixed initial states, not only do any estimation accuracy enhancements typical of the pure initial-state cases survive but that additional advantages emerge. Specifically, we show that the estimation accuracy can increase with more than two qubits in a correlated state and the enhancement in the accuracy for the mixed-state case can exceed the enhancement in the accuracy for the pure initial-state case.

Read this article online: http://dx.doi.org/10.1103/PhysRevA.92.032324

(Session 5 : Thursday from 5:00 - 7:00 pm)

 

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