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

2026-03-17

AI Summary

This work addresses the challenge of performing efficient arbitrary measurements on single-rail qubits in the XY Bloch plane, which is hindered by the absence of strong nonlinear interactions and traditionally limited to a success probability of 1/2. The authors propose a purely linear-optical scheme that combines an unentangled ancillary single-rail qubit, an eight-port interferometer, and single-photon detection to construct a programmable measurement device. This approach surpasses the theoretical 1/2 success probability bound, achieving a record success rate of 147/256 (approximately 57.4%) for arbitrary XY-plane measurements—without requiring any entanglement resources. The result represents a significant advancement in the measurement capabilities of single-rail photonic qubits.

Technology Category

• Machine Learning: Quantum Machine Learning
• Planning, Routing, and Scheduling: Plan Execution and Monitoring
• Intelligent Robots: State Estimation

Application Category

• Security and Privacy: Large-scale security measurements
• Web Mining and Content Analysis: Web measurements
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

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.

Problem

• single-rail qubits
• quantum measurement
• linear optics
• photon detection
• quantum information

Innovation

• single-rail qubits
• linear optics
• unentangled ancillas
• quantum measurement
• interferometry