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Register a new userDisentangling Pauli blocking of atomic decay from cooperative radiation and atomic motion in a 2D Fermi gas
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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 $Lambda$ level structure (one excited and two degenerate ground states). We identify a parameter window in which a factor of two extension in the atomic lifetime clearly attributable to Pauli blocking should be experimentally observable in deeply degenerate gases with $sim 10^{3} $ atoms. Our predictions are supported by observation of a number-dependent excited state decay rate on the ${}^{1}rm{S_0}-{}^{3}rm{P_1}$ transition in $^{87}$Sr atoms.
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Spontaneous decay of an excited atomic state is a fundamental process that originates from the interaction between matter and vacuum modes of the electromagnetic field. The rate of decay can thus be engineered by modifying the density of final states of the joint atom-photon system. Imposing suitable boundary conditions on the electromagnetic field has been shown to alter the density of vacuum modes near the atomic transition, resulting in modified atomic decay rates. Here we report the first experimental demonstration of suppression of atomic radiative decay by reducing the density of available energy-momentum modes of the atomic motion when it is embedded inside a Fermi sea.
We demonstrate clear collective atomic recoil motion in a dilute, momentum-squeezed, ultra-cold degenerate fermion gas by circumventing the effects of Pauli blocking. Although gain from bosonic stimulation is necessarily absent because the quantum gas obeys Fermi-Dirac statistics, collective atomic recoil motion from the underlying wave-mixing process is clearly visible. With a single pump pulse of the proper polarization, we observe two mutually-perpendicular wave-mixing processes occurring simultaneously. Our experiments also indicate that the red-blue pump detuning asymmetry observed with Bose-Einstein condensates does not occur with fermions.
Some thoughts regarding pairing in atomic Fermi gases were considered, meant for starting discussion on the topic.
We propose an experimental scheme to simulate the fractionalization of particle number by using a one-dimensional spin-orbit coupled ultracold fermionic gas. The wanted spin-orbit coupling, a kink-like potential, and a conjugation-symmetry-breaking mass term are properly constructed by laser-atom interactions, leading to an effective low-energy relativistic Dirac Hamiltonian with a topologically nontrivial background field. The designed system supports a localized soliton excitation with a fractional particle number that is generally irrational and experimentally tunable, providing a direct realization of the celebrated generalized-Su-Schrieffer-Heeger model. In addition, we elaborate on how to detect the induced soliton mode with the FPN in the system.
We propose a model for addressing the superfluidity of two different Fermi species confined in a bilayer geometry of square optical lattices. The fermions are assumed to be molecules with interlayer s-wave interactions, whose dipole moments are oriented perpendicularly to the layers. Using functional integral techniques we investigate the BCS-like state induced in the bilayer at finite temperatures. In particular, we determine the critical temperature as a function of the coupling strength between molecules in different layers and of the interlayer spacing. By means of Ginzburg-Landau theory we calculate the superfluid density. We also study the dimerized BEC phase through the Berezinskii-Kosterlitz-Thouless transition, where the effective mass leads to identify the crossover from BCS to BEC regimes. The possibility of tuning the effective mass as a direct consequence of the lattice confinement, allows us to suggest a range of values of the interlayer spacing, which would enable observing this superfluidity within current experimental conditions.
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