Neutral atoms are widely used for quantum computing and quantum information applications due to their scalability and high-fidelity Rydberg i nteractions. Recently, dual-species single atom arrays have been demonstrated in which one species is used for computation and the other is used to perform auxiliary mid-circuit measurements. We propose the co-location of two ensembles of ultracold 85Rb and 87Rb in a crossed-beam optical dipole trap for quantum information applications. Due to the isotope shift, crosstalk between the ensembles is small and each ensemble can be addressed independently. The trapped ensembles can be made to support only a single collective Rydberg excitation while providing robustness against collisional losses. We present progress towards the independent control of two Rb ensembles co-located in a dual-species crossed beam optical dipole trap and discuss measurements of the crosstalk between the ensembles.

We convert atomic photons of the 87Rb D1 transition at 795 nm to telecom photons at 1529 nm with efficiency of 6% by employing four-wave mixing in a warm vapor. Optical pumping enhances the four-wave mixing process, enabling such high efficiency.

We describe the application of structured imaging with a single-pixel camera to imaging through fog. We demonstrate the use of a high-pass filter on the detected bucket signals to suppress the effects of temporal variations of fog density and enable an effective reconstruction of the image. A quantitative analysis and comparison of several high-pass filters are demonstrated for the application. Both computational ghost imaging and compressive sensing techniques were used for image reconstruction and compressive sensing was observed to give a higher reconstructed image quality.

We study decoherence in continuously cooled atom interferometers by performing Raman-Ramsey fringe measurements in a continuous beam of 3D-sub-Doppler-cooled rubidium atoms. The atom beam is produced by a two-stage cold atom source that is designed to mitigate the decoherence of atomic interference caused by cooling induced fluorescence. The atom beam source produces a collimated beam of over 109 atoms/s that is cooled by polarization gradient cooling to temperatures as low as 14 µK. We infer the potential performance of this atom beam source in a cold-atom gyroscope and use numerical models of motion in 6 degrees of freedom to study the expected performance on dynamic platforms.

We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom beam source originates in a pushed two-dimensional magneto-optical trap (2D$^+$ MOT) feeding a slightly off-axis three-dimensional moving optical molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, $\sim 3$ m/s, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross-section of cooling-induced fluorescence. Near-resonance light from the 2D$^+$ MOT and the push beam does not propagate to the output atomic trajectory due to a 10 degree bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to $1.6(3)\times 10^9\;\textrm{atoms/s}$, with an optimized temperature of $15.0(2)\;\mu$K. We employ continuous Raman-Ramsey interference measurements at the atom beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom beam source effectively preserves high fringe contrast even during cooling. This cold-atom beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom beam velocity (6 - 16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.

We convert telecom photons at 1530 nm to atomic photons on the 87Rb D1 transition at 795 nm in a warm vapor with efficiency near 10% by employing efficient optical pumping and four-wave mixing.

We show that, when the integration time of the single photon detectors is longer than the correlation time of the biphoton, the attainable spatial resolution in ghost imaging with entangled signal idler pairs generated in type II spontaneous parametric down conversion is limited by the angular spread of single-frequency-signal idler pairs. If, however, the detector integration time is shorter than the biphoton correlation time, the transverse k-vectors of different spectral components combine coherently in the image, improving the spatial resolution.

Interferometric stability of polarization-entangled photons in quantum repeaters for long time intervals is an important capability for future scalable quantum networks linked over distances greater than hundreds of kilometers. A quantum memory node is a necessary component of the quantum repeater, where entanglement is prepared and swapped to extend entangled states from remote to distant nodes. Room temperature fluctuations can have significant effects on phase stability of the polarization states stored in the quantum memory. Although common-path stabilization in a quantum memory has been demonstrated, passive stabilization to room temperature variations has not been realized. Our approach to the quantum memory uses a single collective excitation encoded in two separate spatial modes in a cold ensemble of rubidium atoms. The two spatial modes are combined into a single path using the birefringence of two calcite crystals. However, normal lab temperature changes introduces a phase shift between the ordinary and extraordinary pathways on the order of 2π. We demonstrate passive temperature stabilization by alignment of the ordinary path in one crystal to the extraordinary path in the second crystal and vice versa. We show a phase stability on the order of ten hours by homodyne detection of classical light modes exiting the interferometer. We corroborate the phase stability of the quantum memory with a correlation measurement between polarization states of a signal photon generated at the formation of the collective atomic excitation and a retrieved idler photon during the destruction of the atomic excitation. We measure a Bell-CHSH parameter for both the unstable configuration and for the stable configuration. For an unstable calcite crystal configuration, we do not measure a violation of the Bell-CHSH inequality1 (S≤2) with S = 1.42 ± 0.087. For the stable calcite crystal configuration, we measure a violation of Bell-CHSH inequality (S>2) with S = 2.48±0.099.

Quantum key distribution (QKD) can be used to produce a cryptographic key whose security is guaranteed by quantum mechanics. The range of fiber-based QKD links is limited, by loss, to a few hundred kilometers, and cannot be used between mobile platforms. Free space QKD can, in principle, overcome these limitations. In practice, very narrow beam divergences must be used, requiring highly accurate pointing of the transmitting terminal to the receiver. This makes deployment very difficult. Here we describe the experimental implementation of a new type of free space QKD link, using modulating retro-reflectors (MRR). The MRR-QKD link eases the pointing requirements by more than three orders of magnitude, from microradians to degrees, while maintaining the narrow beam divergence necessary for long-range communication links. The system uses new, high extinction surface-normal multiple quantum well modulators with a modulation rate of 100 MHz. A laboratory-based BB84 QKD link using multiple quantum well MRRs is demonstrated, link budgets for possible applications are discussed, and security issues are considered.

We report progress toward the development of a chip-based cold atom trap based on nanoscale waveguides, which incorporates a fabricated two-wire magnetic trap to assist in transferring laser-cooled atoms to the waveguides.

With the development of quantum computers, that can break current classical encryption schemes, unconditionally secure quantum key distribution (QKD) will become very important. Current fiber-based QKD implementations are limited to a few hundred kilometers due to optical losses in fiber and cannot be used with mobile platforms. A free space QKD system has recently been demonstrated over very large distances using entangled photons. However, due to the extremely high pointing accuracy required, the implementation of this QKD approach is very challenging and power demanding Here we describe a new type of QKD link that uses modulating retro-reflectors. Our approach reduces pointing requirements by orders of magnitude, allowing an increase in pointing tolerance from microradians to tens of milliradians. Additionally, it reduces power requirements on the moving platform and has potential of reducing some influence of turbulence on the secure key distribution rate. Our approach relies on new, high extinction surface-normal multiple quantum well modulators with a maximum modulation rate of 100 MHz. We report on a BB84 QKD link using our system in the laboratory.

Quantum key distribution (QKD) can be used to produce a cryptographic key whose security is unconditionally guaranteed by quantum mechanics. The range of fiber-based QKD links is limited, by loss, to a few hundred kilometers, and cannot be used between mobile platforms. Free space QKD can, in principle, overcome these limitations. In practice, very narrow beam divergences must be used, requiring highly accurate pointing of the transmitting terminal to the receiver. This makes deployment very difficult. Here we describe an entirely new type of free space QKD link, using modulating retro-reflectors (MRR). The MRR-QKD link eases the pointing requirements A laboratory-based BB84 QKD link using multiple quantum well MRRs is demonstrated, and link budgets for possible applications are discussed.

Quantum key distribution (QKD) using free space optical (FSO) systems will, in most applications, involve atmospheric propagation. As is well known from classical FSO communication links, turbulence can cause large power variation in the link strength. Optical scintillation can cause fades below and surges above the mean power that last tens of milliseconds. Fades can be as deep as 20-30 dB. Previously we have demonstrated a system that allows laboratory studies of the effects of scintillation that faithfully represent the effects seen in the field. Scintillation is recorded using a modified FSO system and then played back in the laboratory using a fiber optic based system. The result is a laboratory experiment that reproduces, with high fidelity, the field conditions and component performance of the actual link. We have applied this same technique to studying scintillation effects on a QKD link. Scintillation was recorded at the US Naval Research Laboratory’s Maritime Lasercom Testbed This facility has sites on both sides of Chesapeake Bay separated by 16 km. A single-photon scintillation playback system was constructed. This scintillation playback system was designed to implement a BB84 protocol, but other QKD protocols could also be used. After the playback experiment the data can be analyzed to determine key length, error rate and other parameters. The set up can be used to study a variety of protocols for QKD in scintillation. Application to studies such as this will be presented.

We describe an optical configuration that is predicted to exhibit the behavior described by Popper in his challenge to conventional quantum mechanics. Popper rejected this behavior on the grounds that it was unphysical because it relied on observer knowledge as a causative agent. We offer an interpretation in which the behavior arises simply out of the mode properties of an entangled system. In this interpretation the observer knowledge reveals in which mode an excitation occurs, but does not affect future behavior as asserted by Popper. We also discuss the relation of our system to the quantum eraser.