Task Progress:
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The project team currently consists of Principal Investigator (PI) Kolkowitz, postdoctoral researchers Dr. Shuo Ma and Dr. Dhruva Ganapathy, graduate students Jonathan Dolde and Anke Stoeltzel, and undergraduate researchers Jenny Chen and Bennett Christensen. Over the course of the first year of performance, we have made significant progress towards our goals, and also developed new techniques and research directions that are complementary to our initial proposed approaches.
We have already achieved the goals of one of the three proposed primary thrusts of our research program, and have even built upon them. We originally proposed the use of two atomic ensembles in a single atomic clock in order to double the operational Ramsey free precession time without incurring phase slips. We successfully experimentally demonstrated this approach, and confirmed that it does indeed significantly enhance the achievable absolute stability of an optical atomic clock operating with otherwise identical resources, including the same local oscillator and the exact same number of atoms. We demonstrated joint Ramsey interrogation of two spatially-resolved strontium-87 atom ensembles that are 90% out of phase with respect to each other, which we call "Quadrature Ramsey spectroscopy", doubling the achievable coherent interrogation time without incurring phase slips and resulting in a factor of 1.36(5) reduction in absolute clock instability as measured with interleaved self-comparisons.
We then went beyond what we had originally proposed, and leveraged the rich hyperfine structure of strontium-87 to realize independent coherent control over multiple ensembles with only global laser addressing. We utilized this independent control over 4 atom ensembles to implement a form of phase estimation, achieving a factor of greater than 3 enhancement in coherent interrogation time and a factor of 2.08(6) reduction in instability over an otherwise identical single ensemble clock with the same local oscillator and the same number of atoms. The manuscript describing this work was published in Physical Review X. [Ed. Note: See Bibliography.] We believe this work represents the start of a new research direction focused on the more efficient allocation and utilization of the resources (both classical and quantum) that make up optical lattice atomic clocks, with the potential for significant improvements in clock stability and accuracy for the same number of atoms, local oscillator, and basic experimental apparatus. We note that we began work on this research thrust immediately after the selection of this grant for funding had been officially announced in March of 2023, but due to administrative delays in the awarding of the grant, we completed this work and published the results before the official start date of the award in July of 2024. However, this work was still enabled by this award and the knowledge that we would be receiving the financial support.
The second primary thrust of this research program focuses on determining what ultimately limits the achievable coherence times and instabilities of synchronous differential clock comparisons. Over the first year of performance, we therefore also undertook a detailed and comprehensive set of measurements to develop a complete model of depolarization and atom loss in strontium-87 optical lattice clocks. We performed lifetime measurements for the 1S0 and 3P0 clock states, where we monitored the populations in both states as a function of time, trap depth, and density, in both strontium-88 and strontium-87. We definitively observed radiative decay on the clock transition of strontium-87, and measured the value for the natural radiative lifetime of this transition to be 167 (+79) (-40) seconds. The manuscript describing these results has been submitted to a physics journal and posted to the physics arXiv.
The final thrust of our research program focuses on characterizing and demonstrating a new "magic wavelength'' "for strontium at 497 nm that has the potential to substantially reduce the optical power requirements for strontium optical lattice clocks. During the first year of performance, we therefore designed, purchased, received, and installed a custom Vertical-External-Cavity Surface-Emitting Laser (VECSEL) laser at 497 nm for this purpose. We expect to begin taking measurements of the 497 nm magic wavelength using this new laser in the coming weeks.
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Articles in Other Journals or Periodicals
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Ma S, Dolde J, Zheng X, Ganapathy D, Shtov A, Chen J, Stoeltzel A, Kolkowitz S. "Enhancing optical lattice clock coherence times with erasure conversion." Physics arXiv preprint server. Posted May 9, 2025. https://doi.org/10.48550/arXiv.2505.06437 , May-2025
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Articles in Other Journals or Periodicals
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Dolde J, Ganapathy D, Zheng X, Ma S, Beloy K, Kolkowitz S. "Direct measurement of the 3P0 clock state natural lifetime in 87Sr." Physics arXiv preprint server. Posted May 9, 2025. https://doi.org/10.48550/arXiv.2505.06440
, May-2025
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Articles in Peer-reviewed Journals
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Niroula P, Dolde J, Zheng X, Bringewatt J, Ehrenberg A, Cox KC, Thompson J, Gullans MJ, Kolkowitz S, Gorshkov AV. "Quantum sensing with erasure qubits." Phys. Rev. Lett. 2024 Aug 23;133(8):080801. https://doi.org/10.1103/PhysRevLett.133.080801 , Aug-2024
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Articles in Peer-reviewed Journals
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Zheng X, Dolde J, Kolkowitz S. "Reducing the instability of an optical lattice clock using multiple atomic ensembles." Physical Review X. 2024 Jan 1;14(1):011006. https://doi.org/10.1103/PhysRevX.14.011006 , Jan-2024
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Awards
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Kolkowitz S. "Experimental Physics Investigator award, The Gordon and Betty Moore Foundation, August 21, 2024." Aug-2024
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