Quantum fluctuations in dipolar gases: Quantum droplets, vortices and impurities

偶极气体中的量子涨落：量子液滴、涡流和杂质

• 批准号: 392530138
• 负责人: Professor Dr. Tilman Pfau
• 金额: --
• 依托单位: 5. Physikalisches Institut
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/392530138?language=en
• 关键词: Quantum; fluctuations; dipolar; gases; droplets

Correlations and fluctuations in a many-body system are the origin of physics beyond mean-field description of the system. This appears naturally if interactions are strong compared to the kinetic energy. In quantum systems, sometimes strong - and microscopically even intractable - quantum correlations can appear and lead to new physics that emerges on the macroscopic scale. However recently it was shown that weak perturbative correlations can also dominate the physics if two weak interactions almost compensate each other on the mean-field level while the fluctuations they induce add up. One first example of this kind of correlation-dominated physics was the surprising discovery of self-bound states of extremely dilute quantum liquids - so called quantum droplets. In this system long and short range interactions compensate each other while their fluctuations stabilize a many-body state that would be unstable on the mean-field level.Here we propose to investigate the fundamental properties of such droplets as well as the applications of these novel isolated quantum objects. We will do so by investigating many-body systems of strongly dipolar dysprosium atoms with a focus on quantum fluctuation effects in dipolar superfluidity, in low dimensions and on fermionic impurities. First, we will dramatically modify the behavior of dipolar quantum fluctuations via the dimensionality of the system. Interestingly, in two dimensions the theoretical description of quantum fluctuations in the presence of dipole-dipole interactions is not known to date calling for experiments to clarify their effect. In one dimension there is first theoretical work on dipolar quantum fluctuations, which however needs to be tested as there are controversial views on the validity of that theory. Again there is clear need for experimental clarification.Second we will investigate the effect of the fluctuations on the superfluid properties of the system. In the crossover from three to quasi-two dimensions we will study the anisotropy of dipolar fluctuations as well as the resulting anisotropy in the Landau critical velocity. Also the transition from Abrikosov vortex lattices to stripe arrangements of vortices will be studied. If those phenomena are observed close to mean-field instabilities they become most susceptible to the effects of fluctuations. Third, an important tool to study thermal and quantum fluctuations is to study dissolved impurities. In the case of a quantum droplet we plan to use the measured number of fermionic impurities in a droplet to do thermometry and determine thermodynamic properties like specific heat. These studies of impurities will try to answer questions on the evaporation process of the droplets. Finally we will investigate the nature of the transition from a gaseous to a liquid state using this tool.

多体系统中的相关性和涨落是系统平均场描述之外的物理起源。如果相互作用比动能强，这就会很自然地出现。在量子系统中，有时会出现强的——微观上甚至难以处理的——量子相关性，并导致宏观尺度上出现新的物理学。然而，最近的研究表明，如果两个弱相互作用在平均场水平上几乎相互补偿，而它们引起的波动加起来，则弱摄动关联也可以支配物理学。这种相关性主导的物理学的第一个例子是对极稀量子液体（即所谓的量子液滴）的自束缚态的惊人发现。在这个系统中，长程和短程相互作用相互补偿，而它们的涨落稳定了在平均场水平上不稳定的多体状态。在这里，我们建议研究这种液滴的基本性质以及这些新型孤立量子物体的应用。为此，我们将研究强偶极镝原子的多体系统，重点研究偶极超流体、低维和费米子杂质中的量子涨落效应。首先，我们将通过系统的维度显著地改变偶极量子涨落的行为。有趣的是，在二维中，偶极子-偶极子相互作用下量子涨落的理论描述至今尚不清楚，需要实验来澄清它们的影响。在一维中，有关于偶极量子涨落的第一个理论工作，然而，由于对该理论的有效性存在争议的观点，因此需要对其进行测试。同样，有必要进行实验澄清。其次，我们将研究波动对系统超流体性质的影响。在从三维到准二维的交叉中，我们将研究偶极波动的各向异性以及由此产生的朗道临界速度的各向异性。此外，还研究了Abrikosov涡格向条纹涡的转变。如果观察到这些现象接近平均场不稳定性，它们就最容易受到波动的影响。第三，研究热涨落和量子涨落的一个重要工具是研究溶解的杂质。在量子液滴的情况下，我们计划使用测量到的费米子杂质的数量来测量温度，并确定热力学性质，如比热。这些对杂质的研究将试图回答有关液滴蒸发过程的问题。最后，我们将使用这个工具来研究从气态到液态转变的性质。