26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Absolute Frequency Noise Characterisation of a 674 nm VECSEL for Trapped Ion Quantum Computing via Three-Cornered Hat Measurement

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster AIP | Quantum Science and Technology (QST)

Description

We report the frequency stabilisation of a 674-nm vertical external-cavity surface-emitting laser (VECSEL) and characterisation of its absolute frequency noise, utilising a three-cornered hat measurement. The 674 nm wavelength addresses the $\textrm{S}_{1/2}$ → $\textrm{D}_{5/2}$ electric quadrupole transition in $^{88}\textrm{Sr}⁺$. This ion species is widely used for quantum computing, including as a network qubit for remote entanglement between separate ion traps in distributed quantum computing experiments. High-fidelity coherent control, needed for remote entanglement and subsequent single- and two-qubit logic gates, requires extremely low and well-characterised laser phase noise, with close-in linewidths at the single-Hz level.

VECSELs have recently emerged as an attractive source at this wavelength, offering high output power, a near-Gaussian mode, and good cost-to-performance ratio. However, their frequency stability and phase noise require rigorous independent characterisation before deployment in quantum information applications. We report the absolute frequency measurement of a 674 nm VECSEL stabilised to a high-finesse ultra-low-expansion (ULE) reference cavity. We first use a three-cornered hat method to establish the absolute phase noise of three ULE reference cavities, using a 674-nm Ti:Sapph laser locked to one cavity and referenced to the other two. By independently analysing the in-loop error of the Ti:Sapph and VECSEL lasers when subsequently locked to two of these cavities, we establish the phase noise of each laser and its lock, and the combined phase noise of the output light. Further verification and insights into the phase noise properties of the respective systems can be achieved via optical beat-note measurement as well as direct precision spectroscopy of single strontium ions.

Preliminary measurements suggest the line-width and noise spectrum of the VECSEL is comparable to that of the existing, deployed 674 nm Ti:Sapph laser, suggesting that the VECSEL platform provides a promising solution for high power coherent manipulations of dipole-forbidden quadrupole transitions in strontium ions.