Session H11: Atomic Clocks

Improved 171Yb Optical Lattice Clock Performance Using Coherent Delocalization

We report on a quantum control technique in an ¹⁷¹Yb optical lattice clock aimed at decreasing the cold collision frequency shift and reducing two-body inelastic losses. Amplitude modulation of a vertically oriented 1D optical lattice realizes Bloch driven coherent delocalization of atoms along the lattice sites. Because Landau-Zener tunneling can be seen to cause sizeable atom loss at very low trap depths (where the tunneling rate is highest), we perform coherent delocalization with the n_z = 2 excited motional band to access higher tunneling rates with limited atom loss. We have observed delocalization that decreases the density of our atomic sample by 4.9(0.6) times. As a result, the cold collision systematic frequency shift is reduced by the same factor, and atom loss due to inelastic two-body loss in the ³P₀ excited state is negligible for our conditions. Higher atom numbers and reduced systematic frequency shifts in atomic clocks can aid in probing new physics for next-generation time and frequency metrology, and even for measuring earth’s gravitational potential.   

Towards a Spin Squeezed Strontium Optical Lattice Clock with Entanglement Enhanced Performance

The exquisite sensitivity of high stability optical atomic clocks provides a broad range of potential applications for probing fundamental physics. By avoiding the Dick noise associated with local oscillators, the current state-of-the-art optical atomic clocks has demonstrated operations at the standard quantum limit (SQL) set by quantum projection noise. Quantum engineering of entangled states of the spin ensemble provides an opportunity to reduce the SQL, resulting in improved measurement precision and frequency stability. In this talk, we report on the recent progress of the implementation of spin squeezed states, generated by cavity-mediated quantum nondemolition measurements in a 1D strontium optical lattice clock, with the aim of demonstrating spin-squeezed clock operations below the SQL.   

Differential clock comparisons with a multiplexed optical lattice clock

Optical lattice clocks are amongst the most accurate and precise devices ever built. Their remarkable stability is now giving rise to a number of novel applications. In this talk, we will report on recent results in which we have implemented a “multiplexed” strontium optical lattice clock, which enables high precision differential frequency comparisons between ensembles of ultracold strontium atoms confined in a mutually shared lattice. We will first discuss our approach to performing synchronous Ramsey interrogation between multiple ensembles, enabling observation of 26 s atom-atom coherence times, and reaching relative instability below 1×10^-17/√τ at 1 s and long-term instability at 10^-20 level simultaneously for up to 10 unique pairwise clock comparisons. Second, we will discuss our progress in measuring the gravitational redshift between ensembles separated in height by less than 1 cm. Finally, we will discuss some exciting prospects for the “multiplexed” clock, such as studying Rydberg-dressed spin-squeezing for quantum enhanced metrology, isotope-shift measurements to search for new forces, and precision tests of fundamental physics.   

A 87Sr SU(10) platform in the Mott-insulating regime

Atomic coherence is a key quantum resource in state-of-the-art optical lattice clocks, enabling record stability via simultaneous interrogation of many atoms. Preparing insulating states of matter at high density in a shallow 3D optical lattice can realize long atomic coherence times, mitigating both tunneling induced dephasing and lattice photon scattering. The SU(10) symmetry of ⁸⁷Sr provides efficient evaporative cooling to achieve a highly degenerate Fermi gas, opening the door to the realization of a well characterized, interacting system in our 3D lattice. Utilizing in situ, saturated fluorescence detection we present results studying this platform operating in the Mott-insulating regime.   

Towards continuous superradiance with a thermal atomic beam

Continuous superradiant lasers have been proposed as next generation optical atomic clocks for precision measurement, metrology, quantum sensing and the exploration of new physics [1].

Superradiance is a collective phenomenon resulting in an enhanced single atom emission rate. A way to provide the required phase synchronization is to exploit a source of cold trapped atoms coherently coupled by a cavity-mediated interaction. Pulsed superradiance has been demonstrated with this technique [2], however steady-state operation remains an open challenge.

We will report on our machine aimed at validating the proposal for a rugged superradiant laser operating on the ¹S₀-³P₁ transition of ⁸⁸Sr using a hot collimated atomic beam [3]. The elegance of this approach is that a single cooling stage and a low finesse cavity appear sufficient to fulfill the requirements for continuous superradiance. Consequently, our device promises a compact, robust and simple optical frequency reference.

The nature of the superradiant phase transition still offers many open questions and drives ongoing studies.  As an outlook we will also elaborate on the potential of our machine as a platform with which to explore new exciting many-body phenomena [4].

[1] Meiser et al., Phys. Rev. Lett. 102, 163601 (2009)

[2] Norcia et al., Sci. Adv. 2, e1601231 (2016),  Schaffer et al., Phys. Rev. A 101, 013819 (2020)

[3] Liu et al., Phys. Rev. Lett. 125, 253602 (2020)

[4] Jäger et al., Phys. Rev. A 103, 013720 (2021)   

Superconducting Nanowire Spectroscopy of the 229Th Isomer

The nucleus of ²²⁹Th has an exceptionally low-energy isomeric transition in the

vacuum-ultraviolet (VUV) spectrum around 8 eV [1]. While a precise measurement of

this transition is difficult with standard nuclear physics techniques, its low

energy provide several new pathways for measuring this laser-accessible nuclear transition.

It has been established that the isomer de-excites primarily via the internal conversion (IC)

channel when neutralized in a solid, with a half-life of 7 μs [2,3]. We will report on an effort

to measure the IC decay of isomeric ²²⁹Th within a superconducting nano-wire single-photon imager (SNSPI).

By leveraging the SNSPI's bias-current-dependent energy responsivity, we aim to measure the

energy released by the isomer into the nano-wire. This in turn will further constrain the

isomer's energy, helping to guide future laser searches.   

Performance of a portable rubidium cold-atom optical clock

There is mounting interest in portable optical atomic clocks for enhancing or replacing GPS timing signals in both commercial and defense-related applications. Optical clocks based on warm vapors are simple in implementation yet performance at long time scales is limited by systematic thermal sensitivities of the system. Vescent, in collaboration with ColdQuanta, has designed and built a portable optical clock based on trapped rubidium atoms to 1) utilize the reduced complexity of rubidium-based systems compared to higher performance cold-atom optical clocks and 2) improve on the long-term performance compared to optical clocks based on hot vapor systems. Current Allan Deviation performance is measured to be 5×10^-12/√τ and is shot-noise limited by the fluorescence detection. Improvements to the systems are on-going, and the size, weight, electrical power, performance, and limitations of the system will be discussed in detail.

    

Withdrawn

In order for an atomic frequency reference to become standardized the impact of aging on its performance must be characterized. We characterize a 3 c.c. buffer gas cooled Yb+ microwave ion trap that was sealed in 2012. The traps consist of a linear quadrupole radio frequency ion trap sealed in a titanium vacuum package backfilled with He. A non-evaporable getter provides passive pumping. Two sapphire viewports are used for coupling 369, 399, 760, and 935 nm laser light into the trap. A third sapphire viewport is used for imaging the trapped ion cloud and ion fluorescence detection.