近日，瑞士洛桑联邦理工学院物理研究所Jean-Philippe Brantut及其研究小组取得一项新进展。经过不懈努力，他们发现了具有光子介导相互作用的幺正费米气体中的密度波有序。相关研究成果已于2023年5月24日在国际权威学术期刊《自然》上发表。
该研究小组在横向驱动的高精度光学腔中成功实现了一个费米气体，同时具备强大且可调谐的接触相互作用以及光子介导的空间结构化长程相互作用。在关键的长程相互作用强度下，系统中稳定出现了密度波有序，研究人员通过超辐射光散射特性确认了这一现象。他们还定量测量了接触相互作用在Bardeen-Cooper-Schrieffer超流态和Bose-Einstein凝聚态过渡范围内对密度波序启动的影响，结果与平均场理论的预期一致。在自有序阈值以下，原子的密度波磁化率在调整长程相互作用的强度和符号时发生了数量级的变化，表明他们能够独立且同时地控制接触和长程相互作用。因此，该研究中的实验设置为研究超流性和密度波序相互作用提供了完全可调谐和微观可控的平台。
据悉，密度波（DW）是与量子物质自组织成晶体结构相关的基本长程序。密度波序与超流性的相互作用可能导致复杂情况，对理论分析提出巨大挑战。在过去几十年中，可调谐的量子费米气体成为研究强相互作用费米子物理的理想模型系统，包括磁序、配对和超流性，以及从Bardeen-Cooper-Schrieffer超流态到Bose-Einstein凝聚态的过渡。
附：英文原文
Title: Density-wave ordering in a unitary Fermi gas with photon-mediated interactions
Author: Helson, Victor, Zwettler, Timo, Mivehvar, Farokh, Colella, Elvia, Roux, Kevin, Konishi, Hideki, Ritsch, Helmut, Brantut, Jean-Philippe
Issue&Volume: 2023-05-24
Abstract: A density wave (DW) is a fundamental type of long-range order in quantum matter tied to self-organization into a crystalline structure. The interplay of DW order with superfluidity can lead to complex scenarios that pose a great challenge to theoretical analysis. In the past decades, tunable quantum Fermi gases have served as model systems for exploring the physics of strongly interacting fermions, including most notably magnetic ordering1, pairing and superfluidity2, and the crossover from a Bardeen–Cooper–Schrieffer superfluid to a Bose–Einstein condensate3. Here, we realize a Fermi gas featuring both strong, tunable contact interactions and photon-mediated, spatially structured long-range interactions in a transversely driven high-finesse optical cavity. Above a critical long-range interaction strength, DW order is stabilized in the system, which we identify via its superradiant light-scattering properties. We quantitatively measure the variation of the onset of DW order as the contact interaction is varied across the Bardeen–Cooper–Schrieffer superfluid and Bose–Einstein condensate crossover, in qualitative agreement with a mean-field theory. The atomic DW susceptibility varies over an order of magnitude upon tuning the strength and the sign of the long-range interactions below the self-ordering threshold, demonstrating independent and simultaneous control over the contact and long-range interactions. Therefore, our experimental setup provides a fully tunable and microscopically controllable platform for the experimental study of the interplay of superfluidity and DW order.
DOI: 10.1038/s41586-023-06018-3
Source: https://www.nature.com/articles/s41586-023-06018-3
Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
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