Optimal quantum-programmable projective measurement with linear optics

TL;DR

This paper introduces a universal, programmable quantum measurement device using linear optics, capable of approximating any projective measurement with optimal accuracy, and demonstrates its practical implementation with simple interferometers.

Contribution

It presents a novel scheme for programmable quantum measurements that extends the swap test, achieving optimality in state discrimination and measurement approximation, with a feasible linear optics setup.

Findings

Achieves optimal state discrimination with one-sided error

Provides a universal scheme for approximating any projective measurement

Proposes a practical linear optics implementation using passive components

Abstract

We present a scheme for a universal device which can be programmed by quantum states to approximate a chosen projective measurement to a given precision. Our scheme can be viewed as an extension of the swap test to the instance where one state is supplied many times. As such, it has many potential applications given the variety of quantum information tasks which make use of the swap test. In particular, we show that our scheme is optimal for state discrimination under the one-sided error requirement, and optimally approximates any projective measurement. Furthermore, we propose a practical implementation of our scheme with passive linear optics, which involves a simple interferometer composed only of balanced beam splitters.