Atomic clocks based on transitions in the visible range of the electromagnetic spectrum, so-called optical atomic clocks, are currently among the most accurate measuring instruments in physics. They use a laser as an extremely high-frequency oscillator whose oscillations are counted by the clock. In order to achieve the highest possible stability over long periods of time, the frequency of the laser is checked against an atomic reference frequency during operation of such a clock and corrected in case of deviations. The long-term stability that can be achieved in the feedback loop results from a compromise between the noise of the laser and quantum mechanical noise of the measurements on the atoms.
Marius Schulte and a team have now investigated in which cases spin squeezed states, a special class of entangled states, can improve stability.
The standard setup of optical clocks with a single ensemble of atoms was investigated and also typical constraints such as additional dead time were considered, where the atoms are prepared and the laser frequency cannot be compared with the reference. The results of the model show that optical atomic clocks with small ensembles of less than about 1,000 atoms can already be improved by squeezed states. With new improvements in laser stability, even the use of squeezed states in atomic clocks with larger ensembles, as for example in optical lattice clocks, becomes reasonable.
The results are important to understand the application of squeezed states in metrology under realistic assumptions. The identified perspectives have a direct influence on the atomic clocks in which the use of squeezed states should already be pursued. Similarly, the challenges motivate to find new ways to improve optical atomic clocks by using squeezed states.
The authors have now published their results in Nature Communications: Prospects and challenges for squeezing-enhanced optical atomic clocks
