Tomography of a displacement photon counter for discrimination of single-rail optical qubits

TL;DR

This paper experimentally evaluates a Kennedy receiver for quantum state discrimination of single-rail optical qubits, demonstrating it surpasses homodyne detection in error rate performance.

Contribution

The study provides the first experimental characterization of a Kennedy receiver for single-rail qubits and compares its performance to Gaussian-based methods.

Findings

Kennedy receiver achieves lower error rates than homodyne detection.

Quantum detector tomography accurately characterizes the measurement operators.

Theoretical minimum error rate with Gaussian transformations is derived.

Abstract

We investigate the performance of a Kennedy receiver, which is known as a beneficial tool in optical coherent communications, to the quantum state discrimination of the two superpositions of vacuum and single photon states corresponding to the $\hat\sigma_x$ eigenstates in the single-rail encoding of photonic qubits. We experimentally characterize the Kennedy receiver in vacuum-single photon two-dimensional space using quantum detector tomography and evaluate the achievable discrimination error probability from the reconstructed measurement operators. We furthermore derive the minimum error rate obtainable with Gaussian transformations and homodyne detection. Our proof of principle experiment shows that the Kennedy receiver can achieve a discrimination error surpassing homodyne detection.