The fundamental constants of nature, by their very definition, are assumed to remain constant across time and space. However, since the late 1930s, there have been suggestions that these constants might vary over time. Interest in such temporal evolution was reignited about 20 years ago by astrophysical observations, however, a significant challenge with astrophysical observations is the difficulty in controlling all relevant parameters. To counteract this, it is natural to conduct highly precise measurements of the time variation of fundamental constants with clocks. While astrophysical observations can examine the cumulative effects of time variation over billions of years, clock-based measurements are limited to much shorter periods, typically spanning days or years. Nevertheless, clocks offer unparalleled precision compared to astrophysical measurements when it comes to detecting potential changes in fundamental constants over time. Therefore, the exceptional precision of clocks makes them invaluable tools for investigating variations in fundamental constants.

The QSNET consortium will create a world-leading programme to search for spatial and temporal variations of fundamental constants using high-precision spectroscopy in networked quantum clocks. The network will include existing Sr, Yb+ and Cs atomic clocks at the National Physical Laboratory in London. In addition, several new clocks are being developed: N2+ molecular ion clock at the University of Sussex, a CaF molecular optical lattice clock at Imperial College London, and a Cf highly-charged ion clock at the University of Birmingham.

Individually, these sensors allow searches for dark matter and dark energy, variations in fundamental constants, Lorentz symmetry breaking, new forces, tests of the equivalence principle, neutrino oscillations and quantum gravity. Collectively, the network will allow greater sensitivity and enable detection of transient effects through correlations in the data from different locations.

Researchers at Imperial College are establishing a molecular lattice clock aimed at examining fluctuations in the proton-to-electron mass ratio over time. This clock will rely on the fundamental vibrational transition found in calcium monofluoride (CaF), oscillating at the Mid-InfraRed frequency of 17.472 THz. To prepare the molecules for incorporation into the lattice, they undergo pre-cooling within a magneto-optical trap, followed by sub-Doppler cooling to achieve microkelvin temperatures. Within the lattice, the clock transition undergoes coherent interrogation using a pair of Raman lasers, each precisely locked to the same high-finesse cavity to ensure frequency stability. This setup allows for driving the clock transition with coherence times on the order of a second, facilitating a sensitive exploration of potential variations in the proton-to-electron mass ratio.

Find out more

You can find out more on the Imperial project page Molecule clock or main QSNET website https://qsnet.org.uk/ .


For more information, please contact Prof. Mike Tarbutt (m.tarbutt@imperial.ac.uk).