Quantum Resource Theory of Lasers

TL;DR

This paper investigates the quantum coherence properties of lasers using resource theory, revealing how spontaneous emission and purity limit coherence and impact quantum information tasks, thus bridging photonics and quantum information science.

Contribution

It introduces a resource theory framework for laser coherence, linking physical laser properties to quantum information capabilities and providing benchmarks for coherent light sources.

Findings

Quantum coherence is limited by spontaneous emission and laser purity.

Laser coherence directly affects the maximum qubit purity achievable.

The study bridges photonics, quantum optics, and quantum information science.

Abstract

Lasers serve as the fundamental workhorses of photonic quantum technologies, with perfectly coherent light fields being essential for many protocols that generate nonclassical light, implement coherent control schemes, and initialize qubits. However, no laser is absolutely ideal and the implications of deviations from perfect coherence in quantum technological tasks remain unclear. In this study, we theoretically and experimentally explore the quantum coherence properties of lasers from a resource theory perspective, establishing a significant connection between photonics, quantum optics, and quantum information science. We demonstrate that the maximum achievable quantum coherence for laser light is constrained by spontaneous emission and the purity of the dephased laser field state. As a critical example application in quantum information protocols, we show that the quantum coherence of a laser field with a given mean photon number directly governs the maximum purity attainable when initializing a qubit in a superposition state through resonant driving. Our findings are highly relevant for bridging applied physics and engineering with integrated photonic quantum technologies and resource theories, paving the way for reliable benchmarking of various coherent light sources for applications in photonics and quantum protocols.