In situ observation of incompressible Mott-insulating domains in ultracold atomic gases

Abstract

The observation of the superfluid to Mott insulator phase transition of ultracold atoms in optical lattices was an enabling discovery in experimental many-body physics, providing the first tangible example of a quantum phase transition (one that occurs even at zero temperature) in an ultracold atomic gas. For a trapped gas, the spatially varying local chemical potential gives rise to multiple quantum phases within a single sample, complicating the interpretation of bulk measurements. Here we report spatially resolved, in-situ imaging of a two-dimensional ultracold atomic gas as it crosses the superfluid to Mott insulator transition, providing direct access to individual characteristics of the insulating, superfluid and normal phases. We present results for the local compressibility in all phases, observing a strong suppression in the insulator domain and suppressed density fluctuations for the Mott insulator, in accordance with the fluctuation-dissipation theorem. Furthermore, we obtain a direct measure of the finite temperature of the system. Taken together, these methods enable a complete characterization of multiple phases in a strongly correlated Bose gas, and of the interplay between quantum and thermal fluctuations in the quantum critical regime.

Thermodynamics of Ultracold Fermi Gases

“…An important exception is the realization of two-dimensional ultracold gases, where the motion is frozen in one direction (here the direction y) using very tight con nement [26,108,109,110]. In that case the optical density is proportional to the surface density n s (x, z) and has a direct physical interpretation (see section 3.1.2).…”

“…As mentioned above, two-dimensional ultracold gases are directly suited for this approach, since n(x, z) is equal to the surface density n S (x, z) (the motion is frozen along y) [26,108,109,110]. In the quasi-2D , minority radius R 2 (dots) and majority radius R 1 (crosses) as a function of polarization P , from [116].…”

Spin Gradient Demagnetization Cooling of Ultracold Atoms

“…The lowest measured temperature is 350±50 picokelvin, making this the coldest implementation of the atomic Mott insulator. An important goal for future experiments will be to develop an additional method of thermometry to measure the temperature of the kinetic degrees of freedom at this very low temperature scale (for progress towards this goal, see Refs [26][27][28]). This temperature is colder than the low-…”

Itinerant magnetic phases and quantum Lifshitz transitions in a three-dimensional repulsively interacting Fermi gas with spin-orbit coupling

“…This fact maybe important for the experimental observation of the phenomena discussed here in the In short, the SOC leads to dramatic changes in essentially all the physical quantities such as the quantum phases, excitations spectra and universality classes of quantum and classical phase transitions. All the novel phenomena can be probed by various established experimental techniques [27][28][29][30][31][32][33]. For example, the collective excitations in the PM (Fig1b), SSDW and LSDW+CDW can be detected by the angle-resolved Bragg spectroscopy [31,32], the order parameters φ T /L in Fig.3 may be directly measured by the time of flight experiments, the evolution of the FS topology in Fig.6 can be monitored by spin-injection RF spectroscopy [33], In the appendix A, we contrast the collective modes in the paramagnet with the SOC which breaks the inversion symmetry and those in the conventional FM state without SOC which breaks the Time reversal symmetry.…”

“…Near to the end of the paper, we briefly discuss the effects of the harmonic trap in observing these phenomena. In view of recent ground breaking experimental realizations of a 2d SOC [7][8][9][10], these new phenomena could be probed [27][28][29][30][31][32][33] in near future cold atom experiments and may also be relevant to some materials with SOC [4,18].…”