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1. High Optical Access Cryogenic System for Rydberg Atom Arrays with a 3000-Second Trap Lifetime

   https://doi.org/10.1103/PRXQuantum.6.020337  

   Zhang, Zhenpu; Hsu, Ting-Wei; Tan, Ting You; Slichter, Daniel H; Kaufman, Adam M; Marinelli, Matteo; Regal, Cindy A (May 2025, PRX Quantum)

   We present an optical tweezer array of 87Rb atoms housed in an cryogenic environment that successfully combines a 4-K cryopumping surface, a <50-K cold box surrounding the atoms, and a room-temperature high-numerical-aperture objective lens. We demonstrate a 3000-s atom-trap lifetime, which enables us to optimize and measure losses at the 10−4 level that arise during imaging and cooling, which are important to array rearrangement. We perform both ground-state qubit manipulation with an integrated microwave antenna and two-photon coherent Rydberg control, with the local electric field tuned to zero via inte- grated electrodes. We anticipate that the reduced blackbody radiation at the atoms from the cryogenic environment, combined with future electrical shielding, should decrease the rate of undesired transitions to nearby strongly interacting Rydberg states, which cause many-body loss and impede Rydberg gates. This low-vibration, high-optical-access cryogenic platform can be used with a wide range of optically trapped atomic or molecular species for applications in quantum computing, simulation, and metrology. 

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2. The Time Programmable Frequency Comb: Generation and Application to Quantum-Limited Dual-Comb Ranging

   https://doi.org/10.48550/arXiv.2205.01147  

   Caldwell, E.D.; Sinclair, L.C.; Newbury, N.R.; Deschenes, J-D (July 2022, ArXivorg)

   The classic self-referenced frequency comb acts as an unrivaled ruler for precision optical metrology in both time and frequency. Two decades after its invention, the frequency comb is now used in numerous active sensing applications. Many of these applications, however, are limited by the tradeoffs inherent in the rigidity of the comb output and operate far from quantum-limited sensitivity. Here we demonstrate an agile programmable frequency comb where the pulse time and phase are digitally controlled with +/- 2 attosecond accuracy. This agility enables quantum-limited sensitivity in sensing applications since the programmable comb can be configured to coherently track weak returning pulse trains at the shot-noise limit. To highlight its capabilities, we use this programmable comb in a ranging system, reducing the detection threshold by ~5,000-fold to enable nearly quantum-limited ranging at mean pulse photon number of 1/77 while retaining the full accuracy and precision of a rigid frequency comb. Beyond ranging and imaging, applications in time/frequency metrology, comb-based spectroscopy, pump-probe experiments, and compressive sensing should benefit from coherent control of the comb-pulse time and phase. 

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3. Strongly interacting Rydberg atoms in synthetic dimensions with a magnetic flux

   https://doi.org/10.1038/s41467-024-46823-6  

   Chen, Tao; Huang, Chenxi; Velkovsky, Ivan; Hazzard, Kaden R. A.; Covey, Jacob P.; Gadway, Bryce (March 2024, Nature Communications)

   Abstract Synthetic dimensions, wherein dynamics occurs in a set of internal states, have found great success in recent years in exploring topological effects in cold atoms and photonics. However, the phenomena thus far explored have largely been restricted to the non-interacting or weakly interacting regimes. Here, we extend the synthetic dimensions playbook to strongly interacting systems of Rydberg atoms prepared in optical tweezer arrays. We use precise control over driving microwave fields to introduce a tunableU(1) flux in a four-site lattice of coupled Rydberg levels. We find highly coherent dynamics, in good agreement with theory. Single atoms show oscillatory dynamics controllable by the gauge field. Small arrays of interacting atoms exhibit behavior suggestive of the emergence of ergodic and arrested dynamics in the regimes of intermediate and strong interactions, respectively. These demonstrations pave the way for future explorations of strongly interacting dynamics and many-body phases in Rydberg synthetic lattices. 

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4. Long-lived Bell states in an array of optical clock qubits

   https://doi.org/10.48550/arXiv.2111.14653  

   Schine, N.; Young, A.W.; Eckner, W.J.; Martin, M. J.; Kaufman, A. M. (July 2022, ArXivorg)

   The generation of long-lived entanglement on an optical clock transition is a key requirement to unlocking the promise of quantum metrology. Arrays of neutral atoms constitute a capable quantum platform for accessing such physics, where Rydberg-based interactions may generate entanglement between individually controlled and resolved atoms. To this end, we leverage the programmable state preparation afforded by optical tweezers along with the efficient strong confinement of a 3d optical lattice to prepare an ensemble of strontium atom pairs in their motional ground state. We engineer global single-qubit gates on the optical clock transition and two-qubit entangling gates via adiabatic Rydberg dressing, enabling the generation of Bell states, |ψ⟩=12√(|gg⟩+i|ee⟩), with a fidelity of F=92.8(2.0)%. For use in quantum metrology, it is furthermore critical that the resulting entanglement be long lived; we find that the coherence of the Bell state has a lifetime of τbc=4.2(6) s via parity correlations and simultaneous comparisons between entangled and unentangled ensembles. Such Bell states can be useful for enhancing metrological stability and bandwidth. Further rearrangement of hundreds of atoms into arbitrary configurations using optical tweezers will enable implementation of many-qubit gates and cluster state generation, as well as explorations of the transverse field Ising model and Hubbard models with entangled or finite-range-interacting tunnellers. 

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5. Quantum sensing and metrology for fundamental physics with molecules

   https://doi.org/10.1038/s41567-024-02499-9  

   DeMille, David; Hutzler, Nicholas R; Rey, Ana Maria; Zelevinsky, Tanya (May 2024, Nature Physics)

   Quantum sensing and metrology use coherent superposition states of quantum systems to detect and measure physical effects of interest. Their sensitivity is typically limited by the standard quantum limit, which bounds the achievable precision in measurements involving nominally identical but uncorrelated quantum systems. Fully quantum metrology involves entanglement in an array of quantum systems, enabling uncertainty reduction below the standard quantum limit. Although ultracold atoms have been widely used for applications such as atomic clocks or gravitational sensors, molecules show higher sensitivity to many interesting phenomena, including the existence of new, symmetry-violating forces mediated by massive particles. Recent advancements in molecular cooling, trapping and control techniques have enabled the use of molecules for quantum sensing and metrology. This Review describes these advancements and explores the potential of the rich internal structure and enhanced coupling strengths of molecules to probe fundamental physics and drive progress in the field. 

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