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Register a new userA supersolid-based gravimeter in a ring cavity
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We propose a novel type of composite light-matter interferometer based on a supersolid-like phase of a driven Bose-Einstein condensate coupled to a pair of degenerate counterpropagating electromagnetic modes of an optical ring cavity. The supersolid-like condensate under the influence of the gravity drags the cavity optical potential with itself, thereby changing the relative phase of the two {cavity electromagnetic fields}. Monitoring the phase evolution of the cavity output fields thus allows for a nondestructive measurement of the gravitational acceleration. We show that the sensitivity of the proposed gravimeter exhibits Heisenberg-like scaling with respect to the atom number. As the relative phase of the cavity fields is insensitive to photon losses, the gravimeter is robust against these deleterious effects. For state-of-the-art experimental parameters, the relative sensitivity $Delta g/g$ of such a gravimeter could be of the order of $10^{-10}$--$10^{-8}$ for a condensate of a half a million atoms and interrogation time of the order of a few seconds.
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We investigate the dynamics of a Bose-Einstein condensate interacting with two non-interfering and counterpropagating modes of a ring resonator. Superfluid, supersolid and dynamic phases are identified experimentally and theoretically. The supersolid phase is obtained for sufficiently equal pump strengths for the two modes. In this regime we observe the emergence of a steady state with crystalline order, which spontaneously breaks the continuous translational symmetry of the system. The supersolidity of this state is demonstrated by the conservation of global phase coherence at the superfluid to supersolid phase transition. Above a critical pump asymmetry the system evolves into a dynamic run-away instability commonly known as collective atomic recoil lasing. We present a phase diagram and characterize the individual phases by comparing theoretical predictions with experimental observations.
Atomic interferometry in optical lattices is a new trend of developing practical quantum gravimeter. Here, we propose a compact and portable gravimetry scheme with an ensemble of ultracold atoms in gravitationally tilted spin-dependent optical lattices. The fast, coherent separation and recombination of atoms can be realized via polarization-synthesized optical lattices. The input atomic wavepacket is coherently split into two parts by a spin-dependent shift and a subsequent $frac{pi}{2}$ pulse. Then the two parts are held for accumulating a relative phase related to the gravity. Lastly the two parts are recombined for interference by a $frac{pi}{2}$ pulse and a subsequent spin-dependent shift. The $frac{pi}{2}$ pulses not only preclude the spin-dependent energies in the accumulated phase, but also avoid the error sources such as dislocation of optical lattices in the holding process. In addition, we develop an analytical method for the sensitivity in multi-path interferometry.
Collective interaction of light with an atomic gas can give rise to superradiant instabilities. We experimentally study the sudden build-up of a reverse light field in a laser-driven high-finesse ring cavity filled with ultracold thermal or condensed atoms. While superradiant Rayleigh scattering from atomic clouds is normally only observed at very low temperatures (i.e. well below $1 mu$K), the presence of the ring cavity enhances cooperativity and allows for superradiance with thermal clouds as hot as several $10 mu$K. A characterization of the superradiance at various temperatures and cooperativity parameters allows us to link it to the collective atomic recoil laser.
We investigate the collective decay dynamics of atoms with a generic multilevel structure (angular momenta $Fleftrightarrow F$) coupled to two light modes of different polarization inside a cavity. In contrast to two-level atoms, we find that multilevel atoms can harbour eigenstates that are perfectly dark to cavity decay even within the subspace of permutationally symmetric states (collective Dicke manifold). The dark states arise from destructive interference between different internal transitions and are shown to be entangled. Remarkably, the superradiant decay of multilevel atoms can end up stuck in one of these dark states, where a macroscopic fraction of the atoms remains excited. This opens the door to the preparation of entangled dark states of matter through collective dissipation useful for quantum sensing and quantum simulation. Our predictions should be readily observable in current optical cavity experiments with alkaline-earth atoms or Raman-dressed transitions.
Cold atoms in an optical lattice execute Bloch-Zener oscillations when they are accelerated. We have performed a theoretical investigation into the case when the optical lattice is the intra-cavity field of a driven Fabry-Perot resonator. When the atoms oscillate inside the resonator, we find that their back-action modulates the phase and intensity of the light transmitted through the cavity. We solve the coupled atom-light equations self-consistently and show that, remarkably, the Bloch period is unaffected by this back-action. The transmitted light provides a way to observe the oscillation continuously, allowing high precision measurements to be made with a small cloud of atoms.
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