Next generation ultrastable lasers: reducing thermal noise limit and overcoming technical limitations with new materials and technologies

The European Metrology Network for Quantum Technologies has targeted the development of ultra-stable lasers and low perturbation cryogenic systems as necessary steps towards realising practical quantum clocks, and related potentially disruptive technologies.

Stable laser frequency sources are fundamental to workable quantum devices, such as to produce photon pairs in quantum communications, known as frequency combs, that are optical devices that shape laser light spectra into discrete, equally spaced frequency lines, for use as reference frequencies.  

However, in practice, the instability of even the most stable lasers limits the resolution of quantum devices, and despite an impressive pace of development this performance barrier may continue to slow development of quantum technologies for some time. Noise from vibrations or temperature fluctuations can be suppressed, but noise from thermal fluctuations, affecting distances between surfaces of laser cavities, remains an unaddressed cause of instability.

The project will lay the groundwork for developing quantum devices with frequency instabilities below 1×10^-17 Hz. Novel methods will be used to optimise laser sources to reduce thermal noise and improve vibration isolation. Closed-cycle cooling for enabling cryogenic operation will be investigated, as well as digital signal processes for optimising laser wavelength for stability.