Quantum clocks depend on more than precise atomic transitions – they also require control systems capable of delivering and detecting extremely weak optical signals with high fidelity. In 2024, EQUS researchers developed a new class of optical filters designed to address this challenge, with potential benefits for clock stability, signal quality and broader photonics-based quantum technologies.

The filters are based on fibre Bragg gratings – microscopic patterns of varying refractive index inside optical fibres. These structures reflect specific wavelengths of light, and by introducing controlled variations in the pattern, the EQUS team was able to suppress strong control beams while allowing single-photon signals to pass through with minimal loss.

Led by PhD candidate Ben Field (University  of Sydney), the study achieved more than 100 dB attenuation of unwanted light – reducing background signal intensity by a factor of 10 billion. This represents a substantial improvement over existing filter technologies and directly supports the requirements of quantum clock systems, which often depend on high dynamic range and low-loss filtering to preserve coherence.

The work complements the EQUS Quantum Clocks flagship, which explores how quantum hardware can improve timekeeping performance. Reliable filtering of control light is essential for isolating quantum signals used in optical readout, feedback and transduction processes.

The filters were fabricated in collaboration with the ANFF Advanced Fibre Bragg Grating Facility at the University of Sydney. The project also drew on expertise from classical photonics and astrophotonics, demonstrating how cross-disciplinary approaches can address hardware bottlenecks in the development of scalable quantum timing systems.