The aim of this work package is to critically evaluate the various methods to realise ultra-stable optical oscillators from quantum systems. While the quantum limits are an important contribution to the instability, for practical application, detrimental effects of the employed means need to be considered. E.g. in the case of active clocks light fields used to entangle atoms can also lead to light shifts that need to be evaluated and that need to be sufficiently stable not to limit the instability at longer averaging times. In the case of trapped ions the spatial separation of entangled qubits in combination with gradients in the surrounding fields can have detrimental effects and if fluctuating lead to decoherence. On the other hand, engineering the entanglement of multiple qubits for specific sensitivities [roo06] in combination with the control and choice over the precise position of individual qubits [kau17, kau17a] can be used to either realise sensor applications or to systematically measure [rus17], control and eliminate such gradients from a clock system.

Depending on the system and the available infrastructure, the stability will be assigned from comparison to other clocks or to ultra-stable cavities. Some of the systems can be evaluated in the individual setup, e.g. alternating between different configurations or by analysing the corresponding measurement noise.

While the accuracy of the newly developed ultrastable sources is not the primary goal of the project, nevertheless for future applications we will also investigate the accuracy that can be obtained with some of the systems. From the results on stability and accuracy achieved in the previous tasks, the future prospects of these methods, for operational optical clocks will be derived.


Lead participant

PTB (Dr Uwe Sterr)