paper

Local asymptotic normality for finite dimensional quantum systems

arXiv:0804.3876 · doi:10.1007/s00220-009-0787-3

Abstract

We extend our previous results on local asymptotic normality (LAN) for qubits, to quantum systems of arbitrary finite dimension . LAN means that the quantum statistical model consisting of identically prepared -dimensional systems with joint state converges as to a statistical model consisting of classical and quantum Gaussian variables with fixed and known covariance matrix, and unknown means related to the parameters of the density matrix . Remarkably, the limit model splits into a product of a classical Gaussian with mean equal to the diagonal parameters, and independent harmonic oscillators prepared in thermal equilibrium states displaced by an amount proportional to the off-diagonal elements. As in the qubits case, LAN is the main ingredient in devising a general two step adaptive procedure for the optimal estimation of completely unknown -dimensional quantum states. This measurement strategy shall be described in a forthcoming paper.

64 pages

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