A technique is proposed to cool Fermi gases to the regime of quantum degeneracy based on the expected inhibition of spontaneous emission due to the Pauli principle. The reduction of the linewidth for spontaneous emission originates a corresponding reduction of the Doppler temperature, which under specific conditions may give rise to a runaway process through which fermions are progressively cooled. The approach requires a combination of a magneto-optical trap as a cooling system and an optical dipole trap to enhance quantum degeneracy. This results in expected Fermi degeneracy factors $T/T_F$ comparable to the lowest values recently achieved, with potential for a direct implementation in optical lattices. The experimental demonstration of this technique should also indirectly provide a macroscopic manifestation of the Pauli exclusion principle at the atomic physics level.
The Pauli exclusion principle is one of the most fundamental manifestations of quantum statistics. Here, we report on its local observation in a spin-polarized degenerate gas of fermions in an optical lattice. We probe the gas with single-site resolution using a new generation quantum gas microscope avoiding the common problem of light induced losses. In the band insulating regime, we measure a strong local suppression of particle number fluctuations and a low local entropy per atom. Our work opens a new avenue for studying quantum correlations in fermionic quantum matter both in and out of eq…
Fermi gas of polar molecules in the Pauli-blocked regime
JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado（科罗拉多大学物理系与美国国家标准技术研究院JILA联合研究所）；ITAMP, Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；California Institute of Technology（加州理工学院）
The Pauli exclusion principle forbids indistinguishable fermions to occupy the same quantum mechanical state. Its implications are profound and it for example accounts for the electronic shell structure of atoms. Here we perform measurements on the scattering of off-resonant light from ultracold gasses of fermionic atoms. For Fermi gases in the quantum degenerate regime, we observe a marked suppression in light scattering as compared to a similarly prepared thermal Bose gas. We attribute the observed increased transmission of light through the quantum degenerate Fermi gas to Pauli blocking, wh…
We employ metastable ultracold $^{173}$Yb atoms to study dynamics in the 1D dissipative Fermi-Hubbard model experimentally and theoretically, and observe a complete inhibition of two-body losses after initial fast transient dynamics. We attribute the suppression of particle loss to the dynamical generation of a highly entangled Dicke state. For several lattice depths and for two- and six-spin component mixtures we find very similar dynamics, showing that the creation of strongly correlated states is a robust and universal phenomenon. This offers interesting opportunities for precision measurem…
The observation of Pauli blocking of atomic spontaneous decay via direct measurements of the atomic population requires the use of long-lived atomic gases where quantum statistics, atom recoil and cooperative radiative processes are all relevant. We develop a theoretical framework capable of simultaneously accounting for all these effects in a regime where prior theoretical approaches based on semi-classical non-interacting or interacting frozen atom approximations fail. We apply it to atoms in a single 2D pancake or arrays of pancakes featuring an effective $Λ$ level structure (one excited an…
Broken rotational and translational symmetries are the hallmarks of solid state materials. In contrast, quantum liquids and gases do not exhibit such properties. However, if we regard the logarithm of the absolute square of a quantum liquid as an energy ${\cal E}= -{\rm ln}|Ψ|^2$, a geometric pattern naturally occurs at the minimum, i.e. the optimal configuration. Such geometric patterns have recently been studied for non-interacting fermions, and have been named "Pauli crystals". However, such patterns exist in all interacting gases (Bose or Fermi), independent of statistics. Here, we present…
We present photo-excitation of ultra-long-range Rydberg molecules as a probe of spatial correlations in quantum gases. Rydberg molecules can be created with well-defined internuclear spacing, set by the radius of the outer lobe of the Rydberg electron wavefunction $R_n$. By varying the principal quantum number $n$ of the target Rydberg state, the molecular excitation rate can be used to map the pair-correlation function of the trapped gas $g^{(2)}(R_n)$. We demonstrate this with ultracold Sr gases and probe pair-separation length scales ranging from $R_n = 1400 - 3200$ $a_0$, which are on the …
We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state. This directly confirms Pauli blocking in momentum space. For the spin-balanced unitary Fermi gas, we observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid tran…
We report on the experimental realization of homogeneous two-dimensional (2D) Fermi gases trapped in a box potential. In contrast to harmonically trapped gases, these homogeneous 2D systems are ideally suited to probe local as well as non-local properties of strongly interacting manybody systems. As a first measurement, we use a local probe to extract the equation of state (EOS) of a non-interacting Fermi gas. We then perform matter wave focusing to extract its momentum distribution and directly observe Pauli blocking in a near unity occupation of momentum states. Finally, we measure the momen…
Friedel oscillations appear in density of Fermi gases due to Pauli exclusion principle and translational symmetry breaking nearby a defect or impurity. In confined Fermi gases, this symmetry breaking occurs also near to boundaries. Here, density oscillations of a degenerate and confined Fermi gas are considered and characterized. True nature of density oscillations are represented by analytical formulas for degenerate conditions. Analytical characterization is first done for completely degenerate case, then temperature effects are also incorporated with a finer approximation. Envelope function…
Tuning Density and Spin Ordering of Degenerate Fermi Gases in an Optical Cavity
College of Physics and Energy, Fujian Normal University（福建师范大学物理与能源学院）；Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials（福建省量子调控与新能源材料重点实验室）；Fujian Provincial Engineering Technology Research Center of Solar Energy Conversion and Energy Storage（福建省太阳能转换与储能工程技术研究中心）
Anomalous Dimers in Quantum Mixtures near Broad Resonances: Pauli Blocking, Fermi Surface Dynamics and Implications
本文研究了在大多数原子组成的量子费米气体中，由泡利阻塞效应引起的反常二聚体在种间共振附近的能量和色散。与真空中不同，我们发现二聚体质量的符号和大小都可以通过费什巴赫共振来调节。我们还研究了粒子-空穴涨落对二聚体色散的影响，证明了费米面附近的粒子-空穴涨落（费米动量为$\hbar k_F$）通常会降低二聚体的有效二体相互作用和结合能.此外，在轻少数原子的限制下，粒子-空穴涨落不利于形成总动量为$\hbar k_F$的二聚体，因为在$\hbar k_F$附近，占主导地位的粒子-空穴涨落出现的模式是最软的。我们的计算表明，近宽种间共振时，少数-多数的质量比$m_B/m_F$小于一个临界值（估计为0.136），在有限动量通道的二聚体在零动量通道的二聚体积极青睐。我们将我们的理论应用于$^{6}$ Li $^{40}$ K，$^{6}$ Li $^{87}$ Rb，$^{40}$ K $^{87}$ Rb和$^{6}$ Li $^{23}$ Na在宽的种间共振附近的量子气体，并讨论了我们计算的局限性和意义.
Phase Coherence of Strongly Interacting Bosons in One-Dimensional Optical Lattices
Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL University, Sorbonne Université（卡斯勒·布罗塞尔实验室，法兰西公学院，法国国家科学研究中心，巴黎文理研究大学，索邦大学）；Université Paris-Saclay, CNRS, LPTMS（巴黎萨克雷大学，法国国家科学研究中心，理论物理与物质研究所）；Institut Universitaire de France (IUF)（法国高等研究院）
We derive an expression for the reduced density matrices of ideal Bose and Fermi gases in the canonical ensemble, which corresponds to the Bloch--De Dominicis (or Wick's) theorem in the grand canonical ensemble for normal-ordered products of operators. Using this expression, we study one- and two-body correlations of homogeneous ideal gases with $N$ particles. The pair distribution function $g^{(2)}(r)$ of fermions clearly exhibits antibunching with $g^{(2)}(0)=0$ due to the Pauli exclusion principle at all temperatures, whereas that of normal bosons shows bunching with $g^{(2)}(0)\approx 2$, …
We study the ground state phase diagram of population balanced and imbalanced ultracold atomic Fermi gases with a short range attractive interaction throughout the crossover from BCS to Bose-Einstein condensation (BEC), in a two-dimensional optical lattice (2DOL) comprised of two lattice and one continuum dimensions. We find that the mixing of lattice and continuum dimensions, together with population imbalance, has an extraordinary effect on pairing and the superfluidity of atomic Fermi gases. In the balanced case, the superfluid ground state prevails the majority of the phase space. However,…
Spin-polarized samples and spin mixtures of quantum degenerate fermionic atoms are prepared in selected excited Bloch bands of an optical chequerboard square lattice. For the spin-polarized case, extreme band lifetimes above $10\,$s are observed, reflecting the suppression of collisions by Pauli's exclusion principle. For spin mixtures, lifetimes are reduced by an order of magnitude by two-body collisions between different spin components, but still remarkably large values of about one second are found. By analyzing momentum spectra, we can directly observe the orbital character of the optical…
We derive the universal relations for an ultracold two-component Fermi gas with spin-orbit coupling (SOC) $\sum_{α,β=x,y,z}λ_{αβ}σ_αp_β$, where $p_{x,y,z}$ and $σ_{x,y,z}$ are the single-atom momentum and Pauli operators for pseudo spin, respectively, and the SOC intensity $λ_{αβ}$ could take arbitrary value. We consider the system with an s-wave short-range interspecies interaction, and ignore the SOC-induced modification for the value of the scattering length. Using the first-quantized approach developed by S. Tan (Phys. Rev. Lett. \textbf{107}, 145302 (2011)), we obtain the short-range and …
We report on the preparation of a quantum degenerate mixture of $^{23}$Na$^{40}$K molecules and $^{40}$K atoms. A deeply degenerate atomic mixture of $^{23}$Na and $^{40}$K atoms with a large number ratio ($N_F/N_B\approx 6$) is prepared by the mode-matching loading of atoms from a cloverleaf-type magnetic trap into a large-volume horizontal optical dipole trap and evaporative cooling in a large-volume three-beam optical dipole trap. About $3.0\times10^4$ $^{23}$Na$^{40}$K ground-state molecules are created through magneto-association followed by stimulated adiabatic Raman passage. The 2D dens…
Universal Random Matrix Behavior of a Fermionic Quantum Gas
Laboratoire Kastler Brossel, ENS-Université PSL, CNRS, Sorbonne Université, Collège de France（卡斯特勒·布罗塞尔实验室，巴黎高等师范学院-巴黎文理研究大学，法国国家科学研究中心，索邦大学，法兰西公学院）；LPTMS, CNRS, Université Paris-Sud, Université Paris-Saclay（理论与实验物理实验室，法国国家科学研究中心，巴黎第十一大学，巴黎萨克雷大学）；JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder（JILA，美国国家标准与技术研究院，科罗拉多大学博尔德分校物理系）；Laboratoire Collisions Agrégats Réactivité, UMR 5589, FERMI, UT3, Université de Toulouse, CNRS（碰撞与聚集反应实验室，法国国家科学研究中心第5589联合研究单位，FERMI，图卢兹第三大学，图卢兹大学，法国国家科学研究中心）；Sorbonne Université, Laboratoire de Physique Théorique et Hautes Energies, CNRS UMR 7589（索邦大学，理论与高能物理实验室，法国国家科学研究中心第7589联合研究单位）
