Direct Observation of the Superfluid Phase Transition in Ultracold Fermi Gases

Abstract

Water freezes into ice, atomic spins spontaneously align in a magnet, liquid helium becomes superfluid: Phase transitions are dramatic phenomena. However, despite the drastic change in the system's behaviour, observing the transition can sometimes be subtle. The hallmark of Bose-Einstein condensation (BEC) and superfluidity in trapped, weakly interacting Bose gases is the sudden appearance of a dense central core inside a thermal cloud. In strongly interacting gases, such as the recently observed fermionic superfluids, this clear separation between the superfluid and the normal parts of the cloud is no longer given. Condensates of fermion pairs could be detected only using magnetic field sweeps into the weakly interacting regime. The quantitative description of these sweeps presents a major theoretical challenge. Here we demonstrate that the superfluid phase transition can be directly observed by sudden changes in the shape of the clouds, in complete analogy to the case of weakly interacting Bose gases. By preparing unequal mixtures of the two spin components involved in the pairing, we greatly enhance the contrast between the superfluid core and the normal component. Furthermore, the non-interacting wings of excess atoms serve as a direct and reliable thermometer. Even in the normal state, strong interactions significantly deform the density profile of the majority spin component. We show that it is these interactions which drive the normal-to-superfluid transition at the critical population imbalance of 70(5)%.

16 pages (incl. Supplemental Material), 5 figures

References in corpus (8)

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Cited by in corpus (147)

• Theory of ultracold Fermi gases
• Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
• Orbital superfluidity in the $P$-band of a bipartite optical square lattice
• Phase diagram of a two-component Fermi gas with resonant interactions
• Three-body recombination in a three-state Fermi gas with widely tunable interactions
• Normal state of a polarized Fermi gas at unitarity
• Phase diagram of a strongly interacting polarized Fermi gas in one dimension
• Ultra-cold Polarized Fermi Gases
• Bragg spectroscopy of a strongly interacting Fermi gas
• Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture
• Pairing states of a polarized Fermi gas trapped in a one-dimensional optical lattice
• Two-terminal transport measurements with cold atoms
• Quasi-one-dimensional polarized Fermi superfluids
• Thermodynamic Measurements in a Strongly Interacting Fermi Gas
• Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in one-dimensional optical lattices
• Phase Transitions and Pairing Signature in Strongly Attractive Fermi Atomic Gases
• Exact quantum Monte Carlo study of one dimensional trapped fermions with attractive contact interactions
• Generic Phase Diagram of Fermion Superfluids with Population Imbalance
• Exact Numerical Study of Pair Formation with Imbalanced Fermion Populations
• Realization of a strongly interacting Bose-Fermi mixture from a two-component Fermi gas
• The FFLO state in the one-dimensional attractive Hubbard model and its fingerprint in the spatial noise correlations
• Fermi gas near unitarity around four and two spatial dimensions
• Direct observation of excitonic instability in Ta2NiSe5
• Finite temperature phase diagram of a polarized Fermi gas in an optical lattice
• Coherent and dissipative dynamics at quantum phase transitions
• Theory of quasi-one dimensional imbalanced Fermi gases
• Zero Temperature Thermodynamics of Asymmetric Fermi Gases at Unitarity
• Energetics and Structural Properties of Trapped Two-Component Fermi Gases
• Trionic phase of ultracold fermions in an optical lattice: A variational study
• Polarized Fermi condensates with unequal masses: Tuning the tricritical point
• Larkin-Ovchinnikov state in resonant Fermi gas
• Pairing in fermionic systems: A quantum information perspective
• Is a gas of strongly interacting atomic fermions a nearly perfect fluid?
• Determination of the Equation of State of a Two-Component Fermi Gas at Unitarity
• FFLO state in 1, 2, and 3 dimensional optical lattices combined with a non-uniform background potential
• Finite temperature phase diagram of a spin-polarized ultracold Fermi gas in a highly elongated harmonic trap
• Mean field thermodynamics of a spin-polarized spherically trapped Fermi gas at unitarity
• Phase structure of mass- and spin-imbalanced unitary Fermi gases
• The effect of population imbalance on the Berezinskii-Kosterlitz-Thouless phase transition in a superfluid Fermi gas
• Spin diffusion in Fermi gases
• Quantum mixtures of ultracold gases of neutral atoms
• Quantum phase diagram of fermion mixtures with population imbalance in one-dimensional optical lattices
• Radio frequency spectroscopy of a strongly imbalanced Feshbach-resonant Fermi gas
• Stable Fulde-Ferrell-Larkin-Ovchinnikov pairing states in 2D and 3D optical lattices
• Superfluid shells for trapped fermions with mass and population imbalance
• Superfluid Expansion of a Strongly Interacting Fermi Gas
• Magnetic Phase Transitions in One-dimensional Strongly Attractive Three-Component Ultracold Fermions
• Probing the FFLO phase by double occupancy modulation spectroscopy
• Phase structure of spin-imbalanced unitary Fermi gases
• Expansion of 1D polarized superfluids: The FFLO state reveals itself
• Casimir interaction among heavy fermions in the BCS-BEC crossover
• Co-existence and shell structures of several superfluids in trapped three-component Fermi mixtures
• Magnetic ordering and quantum statistical effects in strongly repulsive Fermi-Fermi and Bose-Fermi mixtures
• Imbalanced Superfluid Phase of a Trapped Fermi Gas in the BCS-BEC Crossover Regime
• Normal-Superfluid Interface Scattering For Polarized Fermion Gases
• Pair formation and collapse in imbalanced Fermion populations with unequal masses
• Polarized superfluidity in the attractive Hubbard model with population imbalance
• Finite temperature QMC study of the one-dimensional polarized Fermi gas
• Dimer, trimer and FFLO liquids in mass- and spin-imbalanced trapped binary mixtures in one dimension
• Exotic paired states with anisotropic spin-dependent Fermi surfaces
• Vortex Core Structure in Neutral Fermion Superfluids with Population Imbalance
• Visualization of vortex bound states in polarized Fermi gases at unitarity
• Molecular Bose-Einstein condensation in a versatile low power crossed dipole trap
• Non-BCS superfluidity in trapped ultracold Fermi gases
• Small mass- and trap-imbalanced two-component Fermi systems
• Mott insulators and correlated superfluids in ultracold Bose-Fermi mixtures
• Imaginary polarization as a way to surmount the sign problem in ab initio calculations of spin-imbalanced Fermi gases
• Concomitant Modulated Superfluidity In Polarized Fermionic Gases
• Phase separation in imbalanced fermion superfluids beyond mean-field
• Finite temperature phase diagram of trapped Fermi gases with population imbalance
• Resonant enhancement of the FFLO-state in 3D by a one-dimensional optical potential
• Destroying superfluidity by rotating a Fermi gas at unitarity
• Bogoliubov-de Gennes study of trapped spin-imbalanced unitary Fermi gases
• Critical behaviour in one dimension: unconventional pairing, phase separation, BEC-BCS crossover and magnetic Lifshitz transition
• Minimizing nonadiabaticities in optical-lattice loading
• Finite-size and confinement effects in spin-polarized trapped Fermi gases
• Resonant control of elastic collisions between ${}^{23}$Na${}^{40}$K molecules and ${}^{40}$K atoms
• Exact vortex nucleation and cooperative vortex tunneling in dilute BECs
• Trapped Resonant Fermions above Superfluid Transition Temperature
• Collective modes and the speed of sound in the Fulde-Ferrell-Larkin-Ovchinnikov state
• Density profiles of polarized Fermi gases confined in harmonic traps
• Magnetism and quantum phase transitions in spin-1/2 attractive fermions with polarization
• Cold Fermionic Atoms in Two-Dimensional Traps -- Pairing versus Hund's Rule
• Noise correlations of the ultra-cold Fermi gas in an optical lattice
• Collective Excitations of Trapped Imbalanced Fermion Gases
• Nonequilibrium pairing instability in ultracold Fermi gases with population imbalance
• Spinodal decomposition in polarised Fermi superfluids
• Correlation Effects on Atom Density Profiles of 1-D and 2-D Polarized Atomic-Fermi-Gas Loaded on Optical Lattice
• Phase-separated Ferromagnetism in Spin-imbalanced Fermi Atoms Loaded on an Optical Ladder: a DMRG study
• Normal-Superfluid Interface for Polarized Fermion Gases
• Monte Carlo studies of extensions of the Blume-Emery-Griffiths model
• Vortex formation in a rotating two-component Fermi gas
• Larkin-Ovchinnikov superfluidity in a two-dimensional imbalanced atomic Fermi gas
• Narrow-linewidth cooling of ${}^6$Li atoms using the 2S-3P transition
• Superconductivity induced by strong electron-exciton coupling in doped atomically thin semiconductor heterostructures
• The Trapped Polarized Fermi Gas at Unitarity
• Insulating charge density wave for a half-filled SU(N) Hubbard model with an attractive on-site interaction in one dimension
• Spin Susceptibility Above the Superfluid Onset in Ultracold Fermi Gases
• Unitary polarized Fermi gas under adiabatic rotation
• Spin-polarized vortices with reversed circulation
• Inhomogeneity driven by Higgs instability in gapless superconductor
• Polarized fermions in the unitarity limit
• Radial Fulde-Ferrell-Larkin-Ovchinnikov state in a population-imbalanced Fermi gas
• Mott Phase in Polarized Two-component Atomic Fermi Lattice Gas:A Playground for S=1/2 Heisenberg Model in Magnetic Field
• Possible quantum phase-manipulation of a two-leg ladder in mixed-dimensional fermionic cold atoms
• Thermodynamical approaches to efficient sympathetic cooling in ultracold Fermi-Bose atomic mixtures
• Pairing patterns in polarized unitary Fermi gases above the superfluid transition
• Spontaneous spatial order in two-dimensional ferromagnetic spin-orbit coupled uniform spin-1 condensate solitons
• Generalized Galitskii approach for the vertex function of a Fermi gas with resonant interaction
• Heteronuclear fermionic superfluids with spin degrees of freedom
• The self-energy of an impurity in an ideal Fermi gas to second order in the interaction strength
• Thermodynamics of low-dimensional trapped Fermi gases
• Correlated Phases of Population Imbalanced Fermi-Fermi Mixtures on an Optical Lattice
• Dynamical properties of the unitary Fermi gas: collective modes and shock waves
• Collective Modes and Stability of Bose-Fermi Mixtures with a BCS-BEC Crossover
• Quench Dynamics and Emergence of Phase Separation in Two-Component Atomic Bose Gases at Zero Temperature and above the BEC Critical Temperature
• Structure and stability of quasi-two-dimensional boson-fermion mixtures with vortex-antivortex superposed states
• Coupled pair approach for strongly-interacting trapped fermionic atoms
• Suppression or enhancement of the Fulde-Ferrell-Larkin-Ovchinnikov order in a one-dimensional optical lattice with particle correlated tunnelling
• Microscopic Eilenberger theory of Fulde-Ferrell-Larkin-Ovchinnikov states in the presence of vortices
• A Non-Gaussian Variational Approach to Fermi Polarons in One- and Two-dimensional Lattices
• Supersolid-like states in a two-dimensional trapped spin-orbit-coupled spin-1 condensate
• A generalized effective spin-chain formalism for strongly interacting spinor gases in optical lattice
• Effects of boundaries and density inhomogeneity on states of vortex matter in Bose--Einstein condensates at finite temperature
• Phase diagram of imbalanced fermions in optical lattices
• Competition between the Fulde-Ferrell-Larkin-Ovchinnikov phase and the BCS phase in the presence of an optical potential
• Development of an apparatus for cooling 6Li-87Rb Fermi-Bose mixtures in a light-assisted magnetic trap
• Dimensional crossover on multileg attractive-$U$ Hubbard ladders
• Phase diagram of imbalanced strongly interacting fermions on a one-dimensional optical lattice
• Ground states of atomic Fermi gases in a two-dimensional optical lattice with and without population imbalance
• Superfluidity in atomic Fermi gases
• Supersolid-like solitons in two-dimensional nonmagnetic spin-orbit coupled spin-1 and spin-2 condensates
• Spatial order in a two-dimensional spin-orbit-coupled spin-1/2 condensate: superlattice, multi-ring and stripe formation
• Superfluid-Normal Quantum Phase Transitions in an Imbalanced Fermi Gas
• Unitary Fermi gas in the epsilon expansion
• The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas in the presence of impurities
• Spin-polarized superconducting phase in semiconducting system with next-nearest-neighbor hopping on the honeycomb lattice
• Pair-breaking of multi-gap superconductivity under parallel magnetic fields in electric-field-induced surface metallic state
• The normal state of attractive Fermi gases from coupled-cluster theory
• Quantum Monte Carlo study of the metal-insulator crossover in the square-lattice Hubbard model
• Manifold formation and crossings of ultracold lattice spinor atoms in the intermediate interaction regime
• Spontaneous symmetry breaking in rotating condensates of ultracold atoms
• Universality in rotating strongly interacting gases
• Unconventional Color Superconductor
• A Fortran 90 program to solve the Hartree-Fock equations for interacting spin-1/2 Fermions confined in Harmonic potentials
• Odd-frequency superfluidity from a particle-number-conserving perspective
• Molecular regimes in ultracold Fermi gases