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Published on: May 3, 2019
Prospects and challenges for squeezing-enhanced optical atomic clocks.
Marius Schulte1, Christian Lisdat2, Piet O Schmidt2,3
1Institute for Theoretical Physics and Institute for Gravitational Physics (Albert-Einstein-Institute), Leibniz University Hannover, Appelstrasse 2, 30167, Hannover, Germany. marius.schulte@itp.uni-hannover.de.
Spin squeezing enhances optical atomic clock stability for smaller atom numbers, particularly benefiting ion clocks. For larger Sr lattice clocks, significant laser improvements are needed for spin squeezing to offer substantial gains.
Area of Science:
- Atomic, Molecular, and Optical Physics
- Quantum Metrology
- Precision Measurement
Background:
- Optical atomic clocks achieve high accuracy and stability, crucial for precision measurements.
- Spin squeezing entangled atoms offers potential for improved clock stability by reducing quantum projection noise.
- Evaluating the practical benefits of spin squeezing requires considering realistic atomic clock operational features.
Purpose of the Study:
- To investigate the benefits of spin-squeezed states for optical atomic clocks.
- To analyze clock stability under typical Brownian frequency noise-limited laser sources.
- To provide quantitative predictions for optimal clock stability considering dead time and laser noise.
Main Methods:
- Development of an analytic model for the closed servo-loop of an optical atomic clock.
- Incorporation of spin squeezing and realistic laser noise characteristics into the model.
- Comparison of analytic predictions with numerical simulations of the closed servo-loop.
Main Results:
- Spin squeezing offers limited improvement for large atomic ensembles (e.g., Sr lattice clocks) with current laser technology.
- A critical atom number (around 1000 for Sr lattice clocks) exists below which spin squeezing is beneficial.
- Even with a tenfold improvement in laser performance, this critical atom number remains below 100,000 for lattice clocks.
- Ion clocks, using smaller non-scalable ensembles, can already benefit from spin squeezing with current lasers.
Conclusions:
- The practical advantage of spin squeezing in optical atomic clocks is highly dependent on atom number and laser stability.
- Spin squeezing is most beneficial for smaller atomic ensembles like those in ion clocks under current conditions.
- Significant advancements in laser performance are necessary to realize substantial gains from spin squeezing in large-scale lattice clocks.

