TY - JOUR

T1 - Prospects and challenges for squeezing-enhanced optical atomic clocks

AU - Schulte, Marius

AU - Lisdat, Christian

AU - Schmidt, Piet O.

AU - Sterr, Uwe

AU - Hammerer, Klemens

N1 - Funding Information: We acknowledge valuable contributions from I. D. Leroux in initiating the numerical simulation of atomic clocks applied here. This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through CRC 1227 DQ-mat projects A05, A06, B02, B03 and Germany’s excellence strategy-EXC-2123 QuantumFrontiers-390837967. P.O.S. and U.S. acknowledge funding from EMPIR under project USOQS. EMPIR projects are co-funded by the European Union’s Horizon 2020 research and innovation program and the EMPIR participating states.

PY - 2020/11/24

Y1 - 2020/11/24

N2 - Optical atomic clocks are a driving force for precision measurements due to the high accuracy and stability demonstrated in recent years. While further improvements to the stability have been envisioned by using entangled atoms, squeezing the quantum mechanical projection noise, evaluating the overall gain must incorporate essential features of an atomic clock. Here, we investigate the benefits of spin squeezed states for clocks operated with typical Brownian frequency noise-limited laser sources. Based on an analytic model of the closed servo-loop of an optical atomic clock, we report here quantitative predictions on the optimal clock stability for a given dead time and laser noise. Our analytic predictions are in good agreement with numerical simulations of the closed servo-loop. We find that for usual cyclic Ramsey interrogation of single atomic ensembles with dead time, even with the current most stable lasers spin squeezing can only improve the clock stability for ensembles below a critical atom number of about one thousand in an optical Sr lattice clock. Even with a future improvement of the laser performance by one order of magnitude the critical atom number still remains below 100,000. In contrast, clocks based on smaller, non-scalable ensembles, such as ion clocks, can already benefit from squeezed states with current clock lasers.

AB - Optical atomic clocks are a driving force for precision measurements due to the high accuracy and stability demonstrated in recent years. While further improvements to the stability have been envisioned by using entangled atoms, squeezing the quantum mechanical projection noise, evaluating the overall gain must incorporate essential features of an atomic clock. Here, we investigate the benefits of spin squeezed states for clocks operated with typical Brownian frequency noise-limited laser sources. Based on an analytic model of the closed servo-loop of an optical atomic clock, we report here quantitative predictions on the optimal clock stability for a given dead time and laser noise. Our analytic predictions are in good agreement with numerical simulations of the closed servo-loop. We find that for usual cyclic Ramsey interrogation of single atomic ensembles with dead time, even with the current most stable lasers spin squeezing can only improve the clock stability for ensembles below a critical atom number of about one thousand in an optical Sr lattice clock. Even with a future improvement of the laser performance by one order of magnitude the critical atom number still remains below 100,000. In contrast, clocks based on smaller, non-scalable ensembles, such as ion clocks, can already benefit from squeezed states with current clock lasers.

KW - quant-ph

KW - physics.atom-ph

UR - http://www.scopus.com/inward/record.url?scp=85096615422&partnerID=8YFLogxK

U2 - 10.1038/s41467-020-19403-7

DO - 10.1038/s41467-020-19403-7

M3 - Article

VL - 11

JO - Nature Communications

JF - Nature Communications

SN - 2041-1723

IS - 1

M1 - 5955

ER -