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Register a new userPreparing a highly degenerate Fermi gas in an optical lattice
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We propose a method to prepare a sample of fermionic atoms in a three-dimensional (3D) optical lattice at unprecedentedly low temperatures and uniform filling factors. The process involves adiabatic loading of atoms into multiple energy bands of an optical lattice followed by a filtering stage whereby atoms from all but the ground band are removed. Of critical importance is the use of a non-harmonic trapping potential, taken here to be the radial profile of a high-order Laguerre-Gaussian laser beam, to provide external confinement for the atoms. For realistic experimental parameters, this procedure should produce samples with temperatures $sim10^{-3}$ of the Fermi temperature. This would allow the investigation of the low-temperature phase diagram of the Fermi-Hubbard model as well as the initialization of a high-fidelity quantum register.
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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 Paulis 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 lattice. The observations demonstrated here form the basis for exploring the physics of Fermi gases with two paired spin components in orbital optical lattices, including the regime of unitarity.
We demonstrate a novel technique for cooling a degenerate Fermi gas in a crossed-beam optical dipole trap, where high-energy atoms can be selectively removed from the trap by modulating the stiffness of the trapping potential with anharmonic trapping frequencies. We measure the dependence of the cooling effect on the frequency and amplitude of the parametric modulations. It is found that the large anharmonicity along the axial trapping potential allows to generate a degenerate Fermi gas with anisotropic energy distribution, in which the cloud energy in the axial direction can be reduced to the ground state value.
Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of $4 times 10^{-17}$. Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large atom number, and accuracy, which suffers from density-dependent frequency shifts. Here, we demonstrate a scalable solution which takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a $5 times 10^{-19}$ measurement precision in 1 hour of averaging time.
We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we observe a change of the density of states of the system, which is a signature of quasi two dimensional confinement. We also find that the dipolar oscillations of the Fermi gas along the tight lattice are almost completely suppressed.
In this paper we analytically investigate the ground-state properties of a two-dimensional polarized degenerate Fermi gas in a high-finesse optical cavity, which is governed by a generalized Fermi-Dicke model with tunable parameters. By solving the photon-number dependent Bogoliubov-de-Gennes equation, we find rich quantum phases and phase diagrams, which depend crucially on the fermion-photon coupling strength, the fermion-fermion interaction strength, and the atomic resonant frequency (effective Zeeman field). In particular, without the fermion-fermion interaction and with a weak atomic resonant frequency, we find a mixed phase that the normal phase with two Fermi surfaces and the superradiant phase coexist, and reveal a first-order phase transition from this normal phase to the superradiant phase. With the intermediate fermion-fermion interaction and fermion-photon coupling strengths, we predict another mixed phase that the superfluid and superradiant phases coexist. Finally, we address briefly how to detect these predicted quantum phases and phase diagrams in experiments.
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