A low phase noise cavity transmission self-injection locked laser system for atomic physics experiments

TL;DR

This paper presents a self-injection locked diode laser system with a medium finesse cavity that significantly reduces phase noise, enhancing the fidelity of atomic qubit manipulation for quantum computing and spectroscopy.

Contribution

The authors demonstrate a novel cavity-based self-injection locking technique that suppresses phase noise in diode lasers by 20-30 dB, surpassing previous stabilization methods.

Findings

Phase noise suppressed to -110 to -120 dBc/Hz from 100 kHz to >2 MHz.

Improved laser stability enhances quantum gate fidelity and reduces spin flip errors.

Benchmarking with a trapped calcium ion confirms performance improvements.

Abstract

Lasers with high spectral purity are indispensable for optical clocks and coherent manipulation of atomic and molecular qubits for applications such as quantum computing and quantum simulation. Stabilisation of the laser to a reference can provide a narrow linewidth and high spectral purity. However, widely-used diode lasers exhibit fast phase noise that prevents high fidelity qubit manipulation. Here we demonstrate a self-injection locked diode laser system utilizing a medium finesse cavity. The cavity not only provides a stable resonance frequency, but at the same time acts as a low-pass filter for phase noise beyond the cavity linewidth of around 100 kHz, resulting in low phase noise from dc to the injection lock limit. We model the expected laser performance and benchmark it using a single trapped $^{40}$Ca$^{+}$-ion as a spectrum analyser. We show that the fast phase noise of the laser at relevant Fourier frequencies of 100 kHz to >2 MHz is suppressed to a noise floor of between -110 dBc/Hz and -120 dBc/Hz, an improvement of 20 to 30 dB over state-of-the-art Pound-Drever-Hall-stabilized extended-cavity diode lasers. This strong suppression avoids incoherent (spurious) spin flips during manipulation of optical qubits and improves laser-driven gates in using diode lasers with applications in quantum logic spectroscopy, quantum simulation and quantum computation.