Atomic clocks are among the most accurate measuring instruments in the world, but they can still be improved.

Until now, all metrological grade clocks use uncorrelated atoms, thus characterised by a statistical noise called "quantum projection noise", which fundamentally limits their performance. It is known that this limitation can be overcome by using a form of quantum entanglement called "spin squeezing".

However, the lifetime of spin squeezed states produced in the laboratory is typically several orders of magnitude shorter than that required for metrology grade instruments.

Today, a collaboration between SYRTE and Laboratoire Kastler Brossel has produced compressed states with a lifetime of nearly one second, which is sufficient for a metrology-grade clock or sensor.

Being able to hold the fragile quantum state for such a long period of time also allows a better understanding of its ’real life’ properties, with surprising results: the clock signal produced by the intricate state amplifies over time, reaching more than 4 times its expected value, as demonstrated by the researchers. The effect is explained by extremely weak interactions
The effect is explained by extremely weak interactions between the atoms - so weak that they remained invisible in previous short experiments. These interactions conspire with the quantum correlation created to amplify the coupling with the optical microcavity used to detect the atoms.

The microwave clock used in this experiment operates in the regime of the new generation of compact clocks for Global Navigation System satellites, triggering growing hopes for quantum improvements in compact clocks in the near future.

Atom microcircuit with fibre optic microcavities Copyright: J. Reichel

For more:
The link to the scientific paper, published in the journal Physical Review X Quantum:
Observing Spin-Squeezed States under Spin-Exchange Collisions for a Second
Meng-Zi Huang, Jose Alberto de la Paz, Tommaso Mazzoni, Konstantin Ott, Peter Rosenbusch, Alice Sinatra, Carlos L. Garrido Alzar, and Jakob Reichel
PRX Quantum 4, 020322 - Published 8 May 2023

The newson the CNRS/INSU website:

Researcher contact:
At SYRTE:
Carlos Garrido Alzar, IACI team

At the LKB:
Jakob Reichel, Atom Chips Group