We determine the frequency of the ultranarrow 87 Sr 1 S 0-3 P 2 transition by spectroscopy of an ultracold gas. This transition is referenced to four molecular iodine lines that are observed by Doppler-free saturation spectroscopy of hot iodine vapor. The frequency differences between the Sr and the I 2 transitions are measured with an uncertainty of 0.5 MHz. The absolute frequency of the 87 Sr 1 S 0-3 P 2 (F = 7/2) transition is 446 648 775(30) MHz and limited in accuracy by the iodine reference. This work prepares the use of the Sr 1 S 0-3 P 2 transition for quantum simulation and computation.
Imaging and manipulating individual atoms with submicrometer separation can be instrumental for quantum simulation of condensed matter Hamiltonians and quantum computation with neutral atoms. Quantum gas microscope experiments in most cases rely on quite costly solutions. Here we present an open-source design of a microscope objective for atomic strontium consisting solely of off-the-shelf lenses that is diffraction-limited for 461 nm light. A prototype built with a simple stacking design is measured to have a resolution of 0.63(4) µm, which is in agreement with the predicted value. This performance, together with the near diffraction-limited performance for 532 nm light makes this design useful for both quantum gas microscopes and optical tweezer experiments with strontium. Our microscope can easily be adapted to experiments with other atomic species such as erbium, ytterbium, and dysprosium, as well as Rydberg experiments with rubidium.
We study the correlation clustering problem using the quantum approximate optimization algorithm (QAOA) and qudits, which constitute a natural platform for such non-binary problems. Specifically, we consider a neutral atom quantum computer and propose a full stack approach for correlation clustering, including Hamiltonian formulation of the algorithm, analysis of its performance, identification of a suitable level structure for 87Sr and specific gate design. We show the qudit implementation is superior to the qubit encoding as quantified by the gate count. For single layer QAOA, we also prove (conjecture) a lower bound of 0.6367 (0.6699) for the approximation ratio on 3-regular graphs. Our numerical studies evaluate the algorithm's performance by considering complete and Erdős-Rényi graphs of up to 7 vertices and clusters. We find that in all cases the QAOA surpasses the Swamy bound 0.7666 for the approximation ratio for QAOA depths p≥2. Finally, by analysing the effect of errors when solving complete graphs we find that their inclusion severely limits the algorithm's performance.
Casimir forces, related to London-van der Waals forces, arise if the spectrum of electromagnetic fluctuations is restricted by boundaries. There is great interest both from fundamental science and technical applications to control these forces on the nano scale. Scientifically, the Casimir effect being the only known quantum vacuum effect manifesting between macroscopic objects, allows to investigate the poorly known physics of the vacuum. In this work, we experimentally investigate the influence of self-assembled molecular bio and organic thin films on the Casimir force between a plate and a sphere. We find that molecular thin films, despite being a mere few nanometers thick, reduce the Casimir force by up to 14%. To identify the molecular characteristics leading to this reduction, five different bio-molecular films with varying chemical and physical properties were investigated. Spectroscopic data reveal a broad absorption band whose presence can be attributed to the mixing of electronic states of the underlying gold layer and those of the molecular film due to charge rearrangement in the process of self-assembly. Using Lifshitz theory we calculate that the observed change in the Casimir force is consistent with the appearance of the new absorption band due to the formation of molecular layers. The desired Casimir force reduction can be tuned by stacking several monolayers, using a simple self-assembly technique in a solution. The molecules - each a few nanometers long - can penetrate small cavities and holes, and cover any surface with high efficiency. This process seems compatible with current methods in the production of micro-electromechanical systems (MEMS), which cannot be miniaturized beyond a certain size due to `stiction' caused by the Casimir effect. Our approach could therefore readily enable further miniaturization of these devices.
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