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1. Efficient electro-optical modulation on thin-film lithium niobate

   https://doi.org/10.1364/OL.419597  

   Jin, Mingwei; Chen, Jiayang; Sua, Yongmeng; Kumar, Prajnesh; Huang, Yuping (April 2021, Optics Letters)

   Thin-film lithium niobate has emerged as an excellent, multifaceted platform for integrated photonics and opto-electronics, in both classical and quantum domains. We introduce a novel, to the best of our knowledge, dual-capacitor electrode layout for an efficient interface between electrical and optical signals on this platform. It significantly enhances the electro-optical modulation efficiency to an exceptional voltage–length product of $0.64\mathrm{V}\cdot <\#comment/>\mathrm{c}\mathrm{m}$, thereby lowering the required electric power by many times. This technique can boost the performance of growing applications at the interface of integrated electronics and optics, such as microwave photonics, frequency comb generation, and telecommunication transmission. 

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2. Ultrasensitive multispecies spectroscopic breath analysis for real-time health monitoring and diagnostics

   https://doi.org/10.1073/pnas.2105063118  

   Liang, Qizhong; Chan, Ya-Chu; Changala, P. Bryan; Nesbitt, David J.; Ye, Jun; Toscano, Jutta (October 2021, Proceedings of the National Academy of Sciences)

   Breath analysis enables rapid, noninvasive diagnostics, as well as long-term monitoring of human health, through the identification and quantification of exhaled biomarkers. Here, we demonstrate the remarkable capabilities of mid-infrared (mid-IR) cavity-enhanced direct-frequency comb spectroscopy (CE-DFCS) applied to breath analysis. We simultaneously detect and monitor as a function of time four breath biomarkers— ${\mathrm{C}\mathrm{H}}_3$OH, ${\mathrm{C}\mathrm{H}}_4$, ${\mathrm{H}}_2$O, and HDO—as well as illustrate the feasibility of detecting at least six more ( ${\mathrm{H}}_2$CO, ${\mathrm{C}}_2{\mathrm{H}}_6$, OCS, ${\mathrm{C}}_2{\mathrm{H}}_4$, ${\mathrm{C}\mathrm{S}}_2$, and ${\mathrm{N}\mathrm{H}}_3$) without modifications to the experimental apparatus. We achieve ultrahigh detection sensitivity at the parts-per-trillion level. This is made possible by the combination of the broadband spectral coverage of a frequency comb, the high spectral resolution afforded by the individual comb teeth, and the sensitivity enhancement resulting from a high-finesse cavity. Exploiting recent advances in frequency comb, optical coating, and photodetector technologies, we can access a large variety of biomarkers with strong carbon–hydrogen-bond spectral signatures in the mid-IR. 

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3. Efficient pathway to NaCs ground state molecules

   https://doi.org/10.1088/1367-2630/acd411  

   Warner, Claire; Bigagli, Niccolò; Lam, Aden Z.; Yuan, Weijun; Zhang, Siwei; Stevenson, Ian; Will, Sebastian (June 2023, New Journal of Physics)

   Abstract We present a study of two-photon pathways for the transfer of NaCs molecules to their rovibrational ground state. Starting from NaCs Feshbach molecules, we perform bound-bound excited state spectroscopy in the wavelength range from 900 nm to 940 nm, covering more than 30 vibrational states of the $c^3{\mathrm{\Sigma }}^{+}$, $b^3\mathrm{\Pi }$, and $B^1\mathrm{\Pi }$electronic states. Analyzing the rotational substructure, we identify the highly mixed $c^3{\mathrm{\Sigma }}_1^{+}|v=22⟩\sim b^3{\mathrm{\Pi }}_1|v=54⟩$state as an efficient bridge for stimulated Raman adiabatic passage. We demonstrate transfer into the NaCs ground state with an efficiency of up to 88(4)%. Highly efficient transfer is critical for the realization of many-body quantum phases of strongly dipolar NaCs molecules and high fidelity detection of single molecules, for example, in spin physics experiments in optical lattices and quantum information experiments in optical tweezer arrays. 

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4. Complexity of frustration: A new source of non-local non-stabilizerness

   https://doi.org/10.21468/SciPostPhys.15.4.131  

   Odavić, Jovan; Haug, Tobias; Torre, Gianpaolo; Hamma, Alioscia; Franchini, Fabio; Giampaolo, Salvatore Marco (January 2023, SciPost Physics)

   We advance the characterization of complexity in quantum many-body systems by examiningW $W$-states embedded in a spin chain. Such states show an amount of non-stabilizerness or “magic”, measured as the Stabilizer Rényi Entropy, that grows logarithmically with the number of qubits/spins. We focus on systems whose Hamiltonian admits a classical point with extensive degeneracy. Near these points, a Clifford circuit can convert the ground state into aW $W$-state, while in the rest of the phase to which the classical point belongs, it is dressed with local quantum correlations. Topological frustrated quantum spin-chains host phases with the desired phenomenology, and we show that their ground state’s Stabilizer Rényi Entropy is the sum of that of theW $W$-states plus an extensive local contribution. Our work reveals thatW $W$-states/frustrated ground states display a non-local degree of complexity that can be harvested as a quantum resource and has no counterpart in GHZ states/non-frustrated systems. 

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5. An optical atomic clock using $4D_J$ states of rubidium

   https://doi.org/10.1088/2058-9565/ad77ef  

   Duspayev, A.; Owens, C.; Dash, B.; Raithel, G. (September 2024, Quantum Science and Technology)

   Abstract We analyze an optical atomic clock using two-photon $5S_{1/2}\to 4D_J$transitions in rubidium. Four one- and two-color excitation schemes to probe the $4D_{3/2}$and $4D_{5/2}$fine-structure states are considered in detail. We compare key characteristics of Rb $4D_J$and $5D_{5/2}$two-photon clocks. The $4D_J$clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal black-body shifts. Ac Stark shifts from the clock interrogation lasers are compensated by two-color Rabi-frequency matching. We identify a ‘magic’ wavelength near 1060 nm, which allows for in-trap, Doppler-free clock-transition interrogation with lattice-trapped cold atoms. From our analysis of clock statistics and systematics, we project a quantum-noise-limited relative clock stability at the ${10}^{-13}/\sqrt{\tau \left(s\right)}$-level, with integration timeτin seconds, and a relative accuracy of $\sim {10}^{-13}$. We describe a potential architecture for implementing the proposed clock using a single telecom clock laser at 1550 nm, which is conducive to optical communication and long-distance clock comparisons. Our work could be of interest in efforts to realize small and portable Rb clocks and in high-precision measurements of atomic properties of Rb $4D_J$-states. 

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