Boosted linear-optical measurements on single-rail qubits with unentangled ancillas

TL;DR

This paper demonstrates a method to perform arbitrary measurements on single-rail photonic qubits using unentangled ancillas, an interferometer, and photon detection, surpassing previous success probability limits.

Contribution

It introduces a boosted measurement scheme for single-rail qubits that exceeds the prior success probability limit using linear optics and unentangled ancillas.

Findings

Achieves success probability of 147/256 for measurements in the XY plane.

Surpasses the previous success probability limit of 1/2.

Uses an 8-port interferometer with unentangled ancillas and photon detection.

Abstract

Any quantum state of the radiation field, sliced in small non-overlapping space-time bins is a collection of single-rail qubits, each spanning the vacuum and single-photon Fock state of a mode. Quantum logic on these qubits would enable arbitrary measurements on information-bearing light, but is hard due to the lack of strong nonlinearities. With unentangled ancilla single-rail qubits, an $8$-port interferometer and photon detection, we show any single-rail qubit measurement in the $XY$ Bloch plane is realizable with success probability $147/256$, which beats the prior-known $1/2$ limit.