Session Q4: Atom Optics

Evidence for the role of core electrons in Van der Waals atom-surface potentials

Van der Waals (VdW) and Casimir-Polder potentials are the dominant interactions between charge-neutral objects at nano- to micrometer length scales. They have attracted considerable interest in the field of nanotechnology. Understanding of these potentials is important in searches for new forces such as deviations from Newtonian potentials at very short length scales and vacuum friction. We measured ratios of the VdW potential strength (C3) by diffracting different atoms from the same nano-structure. We report ratios of C3 with a precision better than 3\%. At this level of precision we are sensitive to the contribution of core electrons in the atom. These ratios are insensitive to surface properties and independent of the shape of the potential.   

Cavity-EIT with single atoms

Coherent dark states, such as electromagnetically induced transparency (EIT), can be used to control nonlinear effects for light fields. So far, these phenomena have been studied in media involving a macroscopic number of atoms. In order to scale down these systems to the single quantum level of matter (single atoms) and light (single photons) one has to enhance the matter-light interaction. We report on a new experiment where we use a high finesse optical cavity in which an exactly defined number of atoms can be coupled to the mode of the cavity. We discuss prospects for cavity-based EIT with single atoms and will present its first experimental observation.   

Cavity-Mediated Matter Wave Bistability in a Spin-1 Condensate

We study matter wave bistability in a spin-1 Bose-Einstein condensate dispersively coupled to a high-finesse unidirectional ring cavity. A unique feature is that the population exchange among different modes of matter fields are accomplished via the spin-exchange collisions. We show that the interplay between the atomic spin mixing and the cavity light field can lead to a strong matter wave nonlinearity, making matter wave bistability in a cavity at the single-photon level achievable.   

Atom-chip based tunable optomechanical system

The interaction of photons with ultracold atoms inside high-finesse cavities has provided a new perspective on optomechanics. In these systems, atoms act collectively as both a nonlinear dielectric medium and a cantilever strongly coupled to the circulating light field. Contrary to typical solid-state optomechanical systems, these atom-based systems benefit from low thermal occupation number and little coupling to the surroundings. Here, we present an atom-chip based optomechanical setup. Atoms are tightly trapped and freely positioned relative to the standing wave, enabling both linear and quadratic optomechanical couplings. The mechanical resonator frequency and the light-oscillator coupling strength can both be tuned by varying the intracavity field intensity and the detuning from atomic resonance. To date, research efforts have been geared towards optical bistability, optomechanical frequency shift and heating in both coupling regimes. Outstanding goals include quantum-limited measurements of the collective oscillator position. We report on recent results from this work.   

Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics

We investigate the atom-optical analog of degenerate four-wave mixing of photons by colliding two Bose-Einstein condensates (BECs) of metastable helium and measuring the resulting momentum distribution of the scattered atoms with a time and space resolved detector. For the case of photons, phase matching conditions completely define the final state of the system, and in the case of two colliding BECs, simple analogy implies a spherical momentum distribution of scattered atoms. We find, however, that the final momenta of the scattered atoms instead lie on an ellipsoid whose radii are smaller than the initial collision momentum. Our first-principles numerical simulations using the positive-P method and approximate analytical calculations agree well with the measurements, and reveal a subtle interplay between many-body effects, mean-field interaction, and the anisotropy of the source condensate.   

Crystal Atom Optics: Helium on Lithium Fluoride

We report progress on our experiments reflecting Helium from Lithium Fluoride (LiF). We have undertaken a systematic study of the production of atomically flat single crystal LiF surfaces, which are produced by cleaving the crystal. The flatness of the cleaved surface depends on the defect density in the crystal, which we produce via varying doses of gamma irradiation. We measure the flatness via atomic force microscopy, and correlate these results with the reflected intensity of the beam from the crystal. Matter wave effects, such as diffraction of the beam from the crystal surface, will be discussed.   

Long-range interaction of single atoms through nanowires with nontrivial topology of couplings

We investigate the long-range coupling of individual atoms placed close to metallic nanowires. Putting the emitter close to the surface of the wire, a strong Purcell effect can be observed: the emitter will decay into guided surface plasmon modes of the wire with a rate exceeding that of free space by a large factor. This strong coupling is due to the extremely small mode volume of the surface plasmon modes, their being tightly confined near the wire surface. There is an optimal, sub-wavelength emitter-wire distance where the coupling is maximal due to the losses originating from local circulating currents. Placing two emitters along the wire, we observe a strong, wire-mediated long-range interaction between the emitters. As a result, super- and subradiance can occur over distances large compared to the resonant wavelength. The states with enhanced or suppressed decay rate are the symmetric or anti-symmetric Dicke states. Coupling more atoms to a wire network with a nontrivial coupling topology leads to interesting entangled subradiant states of the system.   

A Compact, Transportable, Microchip-Based System for High Repetition Rate Production of Bose-Einstein Condensates

We present a compact, transportable system that produces Bose-Einstein condensates (BECs) near the surface of an integrated atom microchip. Occupying a volume of 0.4~m$^{3}$ and consuming an average power of 525~W, the system contains all of the components needed to produce and image BECs, including an ultra-high vacuum system, lasers, data acquisition hardware, electronics, and imaging equipment. RF evaporative cooling forms nearly-pure condensates containing 1.9$\times $10$^{4} \quad ^{87}$Rb atoms in the $\vert $F=2,m$_{F}$=+2$\rangle $ ground hyperfine state. With trap frequencies of several kHz, evaporative cooling times as short as 1.5~s have been used to create BECs, resulting in production repetition rates as high as 0.3~Hz. The system can be easily reconfigured for use with atom chips having wire patterns designed for different applications. As such, it can serve as a standardized platform for a variety of portable experiments that utilize ultracold matter.   

Subwavelength Optical Microscopy in Far-Field

We present a complete procedure for subwavelenth optical microscopy. The identical atoms are distributed on a plane disk and shined with a standing wave. We rotate the disk to different angles and record the resonant fluorescence spectra in far-field, from which we can obtain their distance and location information. This procedure also works for atomic separation above one wavelength and so provides a seamless microscopy.