Quantum Fluctuation Dynamics of Dispersive Superradiant Pulses in a Hybrid Light-Matter System.

We consider theoretically a driven-dissipative quantum many-body system consisting of an atomic ensemble in a single-mode optical cavity as described by the open Tavis-Cummings model. In this hybrid light-matter system, the interplay between coherent and dissipative processes leads to superradiant pulses with a buildup of strong correlations, even for systems comprising hundreds to thousands of particles. A central feature of the mean-field dynamics is a self-reversal of two spin degrees of freedom due to an underlying time-reversal symmetry, which is broken by quantum fluctuations. We demonstrate a quench protocol that can maintain highly non-Gaussian states over long timescales. This general mechanism offers interesting possibilities for the generation and control of complex fluctuation patterns, as suggested for the improvement of quantum sensing protocols for dissipative spin amplification.

Proposal for a Deterministic Single-Atom Source of Quasisuperradiant N-Photon Pulses.

We propose a single-atom, cavity quantum electrodynamics system, compatible with recently demonstrated, fiber-integrated micro- and nanocavity setups, for the on-demand production of optical number-state, 0N-state, and binomial-code-state pulses. The scheme makes use of Raman transitions within an entire atomic ground-state hyperfine level and operates with laser and cavity fields detuned from the atomic transition by much more than the excited-state hyperfine splitting. This enables reduction of the dynamics to that of a simple, cavity-damped Tavis-Cummings model with the collective spin determined by the total angular momentum of the ground hyperfine level.

Cavity Dark Mode of Distant Coupled Atom-Cavity Systems.

We report on a combined experimental and theoretical investigation into the normal modes of an all-fiber coupled cavity-quantum-electrodynamics system. The interaction between atomic ensembles and photons in the same cavities, and that between the photons in these cavities and the photons in the fiber connecting these cavities, generates five nondegenerate normal modes. We demonstrate our ability to excite each normal mode individually. We study particularly the "cavity dark mode," in which the two cavities coupled directly to the atoms do not exhibit photonic excitation. Through the observation of this mode, we demonstrate remote excitation and nonlocal saturation of atoms.

Rapid Production of Many-Body Entanglement in Spin-1 Atoms via Cavity Output Photon Counting.

We propose a simple and efficient method for generating metrologically useful quantum entanglement in an ensemble of spin-1 atoms that interacts with a high-finesse optical cavity mode. It requires straightforward preparation of N atoms in the m_{F}=0 sublevel, tailoring of the atom-field interaction to give an effective Tavis-Cummings model for the collective spin-1 ensemble, and a photon counting measurement on the cavity output field. The photon number provides a projective measurement of the collective spin length S, which, for the chosen initial state, is heavily weighted around values S≃sqrt[N], for which the corresponding spin states are strongly entangled and exhibit Heisenberg scaling of the metrological sensitivity with N, as quantified by the quantum Fisher information.

Observation of dressed states of distant atoms with delocalized photons in coupled-cavities quantum electrodynamics.

In a cavity quantum electrodynamics (QED) system, where atoms coherently interact with photons in a cavity, the eigenstates of the system are the superposition states of atoms and cavity photons, the so-called dressed states of atoms. When two cavities are connected by an optical fiber with negligible loss, the coherent coupling between the cavities gives rise to photonic normal modes. One of these normal modes is the fiber-dark mode, in which photons are delocalized in the two distant cavities. Here we demonstrate the setting of coupled-cavities QED, where two nanofiber cavity-QED systems are coherently connected by a meter-long low-loss channel in an all-fiber fashion. Specifically, we observe dressed states of distant atoms with delocalized photons of the fiber-dark normal mode. Our system will provide a platform for the study of delocalized atomic and photonic states, photonic many-body physics, and distributed quantum computation.

Cavity QED Engineering of Spin Dynamics and Squeezing in a Spinor Gas.

We propose a method for engineering spin dynamics in ensembles of integer-spin atoms confined within a high-finesse optical cavity. Our proposal uses cavity-assisted Raman transitions to engineer a Dicke model for integer-spin atoms, which, in a dispersive limit, reduces to effective atom-atom interactions within the ensemble. This scheme offers a promising and flexible new avenue for the exploration of a wide range of spinor many-body physics. As an example of this, we present results showing that this method can be used to generate spin-nematic squeezing in an ensemble of spin-1 atoms. With realistic parameters, the scheme should enable substantial squeezing on time scales much shorter than current experiments with spin-1 Bose-Einstein condensates.

Erratum: Realization of the Dicke Model Using Cavity-Assisted Raman Transitions [Phys. Rev. Lett. 113, 020408 (2014)].

This corrects the article DOI: 10.1103/PhysRevLett.113.020408.

Realization of the Dicke model using cavity-assisted Raman transitions.

We realize an open version of the Dicke model by coupling two hyperfine ground states using two cavity-assisted Raman transitions. The interaction due to only one of the couplings is described by the Tavis-Cummings model and we observe a normal mode splitting in the transmission around the dispersively shifted cavity. With both couplings present the dynamics are described by the Dicke model and we measure the onset of superradiant scattering into the cavity above a critical coupling strength.

Scaling law and stability for a noisy quantum system.

We show that a scaling law exists for the near-resonant dynamics of cold kicked atoms in the presence of a randomly fluctuating pulse amplitude. Analysis of a quasiclassical phase-space representation of the quantum system with noise allows a new scaling law to be deduced. The scaling law and associated stability are confirmed by comparison with quantum simulations and experimental data.

Ballistic and localized transport for the atom optics kicked rotor in the limit of a vanishing kicking period.

We present mean energy measurements for the atom optics kicked rotor as the kicking period tends to zero. A narrow resonance is observed marked by quadratic energy growth, in parallel with a complete freezing of the energy absorption away from the resonance peak. Both phenomena are explained by classical means, taking proper account of the atoms' initial momentum distribution.

Deviations from early-time quasilinear behavior for the atom-optics kicked rotor near the classical limit.

We present experimental measurements of the mean energy for the atom-optics kicked rotor after just two kicks. The energy is found to deviate from the quasilinear value for small kicking periods. The observed deviation is explained by recent theoretical results which include the effect of a nonuniform initial momentum distribution, previously applied only to systems using much colder atoms than ours.

Observation of robust quantum resonance peaks in an atom optics kicked rotor with amplitude noise.

The effect of pulse train noise on the quantum resonance peaks of the atom optics kicked rotor is investigated experimentally. Quantum resonance peaks in the late time mean energy of the atoms are found to be surprisingly robust against all levels of noise applied to the kicking amplitude, while even small levels of noise on the kicking period lead to their destruction. The robustness to amplitude noise of the resonance peak and of the fall-off in mean energy to either side of this peak are explained in terms of the occurrence of stable, epsilon classical dynamics [Nonlinearity 16, 1381 (2003)]] around each quantum resonance.

Unconditional preparation of entanglement between atoms in cascaded optical cavities.

We propose a scheme to unconditionally entangle the internal states of atoms trapped in separate high-finesse optical cavities. The scheme uses the technique of quantum reservoir engineering in a cascaded cavity-QED setting, and for ideal (lossless) coupling between the cavities generates an entangled pure state. Highly entangled states are also shown to be possible for realizable cavity-QED parameters and with nonideal coupling.