Photon number resolution using a time-multiplexed single-photon detector

Photon number resolving detectors are needed for a variety of applications including linear-optics quantum computing. Here we describe the use of time-multiplexing techniques that allows ordinary single photon detectors, such as silicon avalanche photodiodes, to be used as photon number-resolving detectors. The ability of such a detector to correctly measure the number of photons for an incident number state is analyzed. The predicted results for an incident coherent state are found to be in good agreement with the results of a proof-of-principle experimental demonstration.Comment: REVTeX4, 6 pages, 8 eps figures, v2: minor changes, v3: changes in response to referee report, appendix added, 1 reference adde

Preliminary Arc-Jet tests of ablator/RSI joints in simulated space shuttle ascent and entry heating

Five ablator/RSI panels were tested in simulated Shuttle heating conditions to determine heat pulse effects on the ablator and the ablator/RSI joints. Two of the panels were subjected to both ascent and entry heating. The other three panels were subjected to entry heating only. The double-pulse heating (ascent plus entry) had no significant effect on char-layer integrity. Evaluation of the effects of entry heating on the ablator/RSI joints was difficult because, with the panel configuration used, severe pressure gradients developed within some of the joints during testing causing hot-gas flow through the joints. In joints where pressure leaks apparently did not develop, temperatures within the joints were reasonable compared to ablator and RSI back surface temperatures

Thermal performance of a mechanically attached ablator tile for on-orbit repair of shuttle TPS

The reusable surface insulation (RSI) material used in the shuttle thermal protection system is susceptible to damage. If any RSI tiles are damaged or lost during ascent, they must be repaired or replaced prior to entry. One approach to replacing a damaged or missing RSI tile consists of mechanically attaching a tile of ablation material in the place of the RSI tile. The thermal performance of this type of repair tile was evaluated in a simulated entry heating environment. The test specimen consisted of the ablator repair tile mechanically fastened to the strain isolation pad and surrounded by RSI tiles. The evaluation of the thermal performance was based on temperature response, surface integrity, and predicted flight performance. When the ablator tile protruded 1/8 inch above the surrounding RSI tiles, the forward facing steps caused significant inflow of hot gas down the ablator RSI joints and this inflow caused greatly increased back surface temperatures

All-Optical Switching Demonstration using Two-Photon Absorption and the Classical Zeno Effect

Low-contrast all-optical Zeno switching has been demonstrated in a silicon nitride microdisk resonator coupled to a hot atomic vapor. The device is based on the suppression of the field build-up within a microcavity due to non-degenerate two-photon absorption. This experiment used one beam in a resonator and one in free-space due to limitations related to device physics. These results suggest that a similar scheme with both beams resonant in the cavity would correspond to input power levels near 20 nW.Comment: 4 pages, 5 figure

Heralded generation of entangled photon pairs

Entangled photons are a crucial resource for quantum communication and linear optical quantum computation. Unfortunately, the applicability of many photon-based schemes is limited due to the stochastic character of the photon sources. Therefore, a worldwide effort has focused in overcoming the limitation of probabilistic emission by generating two-photon entangled states conditioned on the detection of auxiliary photons. Here we present the first heralded generation of photon states that are maximally entangled in polarization with linear optics and standard photon detection from spontaneous parametric down-conversion. We utilize the down-conversion state corresponding to the generation of three photon pairs, where the coincident detection of four auxiliary photons unambiguously heralds the successful preparation of the entangled state. This controlled generation of entangled photon states is a significant step towards the applicability of a linear optics quantum network, in particular for entanglement swapping, quantum teleportation, quantum cryptography and scalable approaches towards photonics-based quantum computing

Comparison of LOQC C-sign gates with ancilla inefficiency and an improvement to functionality under these conditions

We compare three proposals for non-deterministic C-sign gates implemented using linear optics and conditional measurements with non-ideal ancilla mode production and detection. The simplified KLM gate [Ralph et al, Phys.Rev.A {\bf 65}, 012314 (2001)] appears to be the most resilient under these conditions. We also find that the operation of this gate can be improved by adjusting the beamsplitter ratios to compensate to some extent for the effects of the imperfect ancilla.Comment: to appear in PR

Experimental storage of photonic polarization entanglement in a broadband loop-based quantum memory

We describe an experiment in which one member of a polarization-entangled photon pair is stored in an active "loop and switch" type quantum memory device, while the other propagates through a passive optical delay line. A comparison of Bell's inequality tests performed before and after the storage is used to investigate the ability of the memory to maintain entanglement, and demonstrate a rudimentary entanglement distribution protocol. The entangled photons are produced by a conventional Spontaneous Parametric Down Conversion source with center wavelengths at 780 nm and bandwidths of $\sim$10 THz, while the memory has an even wider operational bandwidth that is enabled by the weakly dispersive nature of the Pockels effect used for polarization-insensitive switching in the loop-based quantum memory platform.Comment: 6 pages, 4 figure

Angle of Repose and Angle of Marginal Stability: Molecular Dyanmics of Granular Particles

We present an implementation of realistic static friction in molecular dynamics (MD) simulations of granular particles. In our model, to break contacts between two particles, one has to apply a finite amount of force, determined by the Coulomb criterion. Using a two dimensional model, we show that piles generated by avalanches have a {\it finite} angle of repose $\theta_R$ (finite slopes). Furthermore, these piles are stable under tilting by an angle smaller than a non-zero tilting angle $\theta_T$, showing that $\theta_R$ is different from the angle of marginal stability $\theta_{MS}$, which is the maximum angle of stable piles. These measured angles are compared to a theoretical approximation. We also measure $\theta_{MS}$ by continuously adding particles on the top of a stable pile.Comment: 14 pages, Plain Te