Quantum State Discrimination Circuits Inspired by Deutschian Closed Timelike Curves

TL;DR

This paper presents a practical quantum circuit method inspired by Deutschian closed timelike curves for discriminating multiple non-orthogonal quantum states, achieving optimal asymptotic performance and implementability.

Contribution

It introduces a new circuit-based approach for quantum state discrimination inspired by D-CTCs, with proven optimality and experimental feasibility.

Findings

Achieves the multiple Chernoff bound for pure qubit states

Characterizes the circuit's asymptotic performance

Recasts the circuit as a local, adaptive implementation

Abstract

It is known that a party with access to a Deutschian closed timelike curve (D-CTC) can perfectly distinguish multiple non-orthogonal quantum states. In this paper, we propose a practical method for discriminating multiple non-orthogonal states, by using a previously known quantum circuit designed to simulate D-CTCs. This method relies on multiple copies of an input state, multiple iterations of the circuit, and a fixed set of unitary operations. We first characterize the performance of this circuit and study its asymptotic behavior. We also show how it can be equivalently recast as a local, adaptive circuit that may be implemented simply in an experiment. Finally, we prove that our state discrimination strategy achieves the multiple Chernoff bound when discriminating an arbitrary set of pure qubit states.