Linearly independent pure-state decomposition and quantum state discrimination

Abstract

We put the pure-state decomposition mathematical property of a mixed state to a physical test. We begin by characterizing all the possible decompositions of a rank-two mixed state by means of the complex overlap between two involved states. The physical test proposes a scheme of quantum state recognition of one of the two linearly independent states which arise from the decomposition. We find that the two states associated with the balanced pure-state decomposition have the smaller overlap modulus and therefore the smallest probability of being discriminated conclusively, while in the nonconclusive scheme they have the highest probability of having an error. In addition, we design an experimental scheme which allows to discriminate conclusively and optimally two nonorthogonal states prepared with different a priori probabilities. Thus, we propose a physical implementation for this linearly independent pure-state decomposition and state discrimination test by using twin photons generated in the process of spontaneous parametric down conversion. The information-state is encoded in one photon polarization state whereas the second single-photon is used for heralded detection.

A measure for maximum similarity between outcome states

“…It is worth noting that the measurement basis leading to the maximum overlap is unbiased with the Schmidt basis of the shared state |ψ and the corresponding probabilities are p λ ⊥ a = p λa = 1/2 [15]. Besides, since the concurrence [5] of |ψ is C ab = 2|α||β|, then we obtain the following relation:…”

Equidistant-state preparation

“…In practice, a nonorthogonal set of states can be generated by projecting pure bipartite states in an appropriate (orthogonal) basis in the Hilbert space of one subsystem [10].…”