Quantum Interference between Photons from an Atomic Ensemble and a Remote Atomic Ion.

Many remote-entanglement protocols rely on the generation and interference of photons produced by nodes within a quantum network. Quantum networks based on heterogeneous nodes provide a versatile platform by utilizing the complementary strengths of the differing systems. Implementation of such networks is challenging, due to the disparate spectral and temporal characteristics of the photons generated by the different quantum systems. Here, we report on the observation of quantum interference between photons generated from a single ion and an atomic ensemble. The photons are produced on demand by each source located in separate buildings, in a manner suitable for quantum networking. Given these results, we analyze the feasibility of hybrid ion-ensemble remote entanglement generation.

Electromagnetically induced transparency in inhomogeneously broadened solid media.

We study, theoretically and experimentally, electromagnetically induced transparency (EIT) in two different solid-state systems. Unlike many implementations in homogeneously broadened media, these systems exhibit inhomogeneous broadening of their optical and spin transitions typical of solid-state materials. We observe EIT lineshapes typical of atomic gases, including a crossover into the regime of Autler-Townes splitting, but with the substitution of the inhomogeneous widths for the homogeneous values. We obtain quantitative agreement between experiment and theory for the width of the transparency feature over a range of optical powers and inhomogeneous linewidths. We discuss regimes over which analytical and numerical treatments capture the behavior. As solid-state systems become increasingly important for scalable and integratable quantum optical and photonic devices, it is vital to understand the effects of the inhomogeneous broadening that is ubiquitous in these systems. The treatment presented here can be applied to a variety of systems, as exemplified by the common scaling of experimental results from two different systems.

Anomalous Broadening in Driven Dissipative Rydberg Systems.

We observe interaction-induced broadening of the two-photon 5s-18s transition in ^{87}Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly 2 orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with blackbody induced population in nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms.

Quantum simulation. Two-dimensional superexchange-mediated magnetization dynamics in an optical lattice.

The interplay of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study nonequilibrium magnetization dynamics in an extended two-dimensional (2D) system by loading effective spin-1/2 bosons into a spin-dependent optical lattice and use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a nonequilibrium antiferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the parameters associated with superexchange and tunneling. With tunneling off-resonantly suppressed, we observe superexchange-dominated dynamics over two orders of magnitude in magnetic coupling strength. Our experiment will serve as a benchmark for future theoretical work as the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques.

Storage and retrieval of collective excitations on a long-lived spin transition in a rare-earth ion-doped crystal.

Robust, long-lived optical quantum memories are important components of many quantum information and communication protocols. We demonstrate coherent generation, storage, and retrieval of excitations on a long-lived spin transition via spontaneous Raman scattering in a rare-earth ion-doped crystal. We further study the time dynamics of the optical correlations in this system. This is the first demonstration of its kind in a solid and an enabling step toward realizing a solid-state quantum repeater.

Enhancing image contrast using coherent states and photon number resolving detectors.

We experimentally map the transverse profile of diffractionlimited beams using photon-number-resolving detectors.We observe strong compression of diffracted beam profiles for high detected photon number. This effect leads to higher contrast than a conventional irradiance profile between two Airy disk-beams separated by the Rayleigh criterion.