An optical frequency comb to support the quantum technology for fundamental physics programme

Despite the tremendous successes in understanding Nature at its most fundamental level, from the tiniest constituents to the largest structures in the Universe, there remain great gaps in our knowledge. We do not understand gravity at the quantum level. Most of the matter in the Universe is some invisible and unknown substance that we call dark matter.

And the expansion of the Universe is accelerating, driven by some unknown force that we call dark energy. There are many theories of quantum gravity, dark matter and dark energy, but little experimental evidence to support them or distinguish between them.

Several new experiments based on the latest developments in quantum science and technology aim to shed light on these mysteries. For example, many theories of quantum gravity, dark matter and dark energy predict that fundamental constants of nature, such as the electron mass divided by the proton mass, should actually vary in space or time. This prediction can be tested by comparing the tick rate of different clocks, based on different atoms and molecules, and looking to see whether this changes over time. A network of such precise clocks is being built in the UK, and these clocks are developing well.

There is a crucial piece of equipment we need in order to compare different clocks. This equipment is known as an optical frequency comb. It is a laser that emits thousands of frequency components that are perfectly uniformly spaced.

The frequency of every component can be determined to extremely high precision. This is the tool that tells us how the frequency of one clock compares to the frequency of another, and whether this frequency ratio is changing over time. Remarkably, with the help of the frequency comb, the clocks do not even need to be at the same location - they can be compared across an optical fibre network.

The aim of this proposal is to acquire the frequency comb so that the quantum technologies we are building can fulfil their potential for testing the foundations of fundamental physics and discovering what lies beyond the limits of our current knowledge.