Quantum-amplified global-phase spectroscopy on an optical clock transition.
basic_science · Level V
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- Record sourced from PubMed, PMID 41062728.
- Also identified by DOI 10.1038/s41586-025-09578-8.
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Abstract
Optical lattice clocks are at the forefront of precision metrology<sup>1-6</sup>, operating near a standard quantum limit set by quantum noise<sup>4,7</sup>. Harnessing quantum entanglement offers a promising route to surpass this limit<sup>8-15</sup>; however, there are practical difficulties in terms of scalability and measurement resolution requirements<sup>16,17</sup>. Here we adapt the holonomic quantum gate concept<sup>18</sup> to develop a new Rabi-type 'global-phase spectroscopy' that uses the detuning-sensitive global Aharonov-Anandan phase<sup>19</sup>. With this approach, we can demonstrate quantum-amplified time-reversal spectroscopy on an optical clock transition that achieves directly measured 2.4(7) dB metrological gain and 4.0(8) dB improvement in laser noise sensitivity beyond the standard quantum limit. To this end, we introduce rotary echo to protect the dynamics from inhomogeneities in light-atom coupling and implement a laser-noise-cancelling differential measurement through symmetric phase encoding in two nuclear spin states. Our technique is not limited by measurement resolution, scales easily because of the global nature of entangling interaction and exhibits high resilience to typical experimental imperfections. We expect it to be broadly applicable to next-generation atomic clocks and other quantum sensors approaching the fundamental quantum precision limits<sup>20-22</sup>.