Experimental quantum state discrimination using the optimal fixed rate of inconclusive outcomes strategy

TL;DR

This paper experimentally demonstrates an optimal quantum state discrimination strategy that balances unambiguous and minimum error approaches by adjusting the inconclusive outcome rate, using a versatile setup with single photons.

Contribution

It introduces a practical experimental scheme for implementing the optimal FRIO measurement on non-orthogonal quantum states with adjustable inconclusive outcomes.

Findings

Successful implementation of the FRIO protocol with high fidelity

Versatile scheme applicable to any pair of non-orthogonal states

Excellent agreement between experimental results and theoretical predictions

Abstract

The problem of non-orthogonal state discrimination underlies crucial quantum information tasks, such as cryptography and computing protocols. Therefore, it is decisive to find optimal scenarios for discrimination among quantum states. We experimentally investigate the strategy for the optimal discrimination of two non-orthogonal states considering a fixed rate of inconclusive outcomes (FRIO). The main advantage of the FRIO strategy is to interpolate between unambiguous and minimum error discrimination by solely adjusting the rate of inconclusive outcomes. We present a versatile experimental scheme that performs the optimal FRIO measurement for any pair of generated non-orthogonal states with arbitrary a priori probabilities and for any fixed rate of inconclusive outcomes. Considering different values of the free parameters in the FRIO protocol, we implement it upon qubit states encoded in the polarization mode of single photons generated in the spontaneous parametric down-conversion process. Moreover, we resort to a newfangled double-path Sagnac interferometer to perform a three-outcome non-projective measurement required for the discrimination task, showing excellent agreement with the theoretical prediction. This experiment provides a practical toolbox for a wide range of quantum state discrimination strategies using the FRIO scheme, which can greatly benefit quantum information applications and fundamental studies in quantum theory.