Nondestructive Detection of an Optical Photon

All optical detectors to date annihilate photons upon detection, thus excluding repeated measurements. Here, we demonstrate a robust photon detection scheme which does not rely on absorption. Instead, an incoming photon is reflected off an optical resonator containing a single atom prepared in a superposition of two states. The reflection toggles the superposition phase which is then measured to trace the photon. Characterizing the device with faint laser pulses, a single-photon detection efficiency of 74% and a survival probability of 66% is achieved. The efficiency can be further increased by observing the photon repeatedly. The large single-photon nonlinearity of the experiment should enable the development of photonic quantum gates and the preparation of novel quantum states of light.Comment: published online in Science Express, 14 November 201

Efficient Teleportation between Remote Single-Atom Quantum Memories

We demonstrate teleportation of quantum bits between two single atoms in distant laboratories. Using a time-resolved photonic Bell-state measurement, we achieve a teleportation fidelity of (88.0+/-1.5)%, largely determined by our entanglement fidelity. The low photon collection efficiency in free space is overcome by trapping each atom in an optical cavity. The resulting success probability of 0.1% is almost 5 orders of magnitude larger than in previous experiments with remote material qubits. It is mainly limited by photon propagation and detection losses and can be enhanced with a cavity-based deterministic Bell-state measurement.Comment: 7 pages, 4 figures, 1 tabl

Heralded Storage of a Photonic Quantum Bit in a Single Atom

Combining techniques of cavity quantum electrodynamics, quantum measurement, and quantum feedback, we have realized the heralded transfer of a polarization qubit from a photon onto a single atom with 39% efficiency and 86% fidelity. The reverse process, namely, qubit transfer from the atom onto a given photon, is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In contrast to previous work based on two-photon interference, our scheme is robust against photon arrival-time jitter and achieves much higher efficiencies. Thus, it constitutes a key step toward the implementation of a long-distance quantum network.Comment: 6 pages, 4 figure

Optimization and Design for Heavy Lift Launch Vehicles

The simulation and evaluation of an orbital launch vehicle requires consideration of numerous factors. These factors include, but are not limited to the propulsion system, aerodynamic effects, rotation of the earth, oblateness, and gravity. A trajectory simulation that considers these different factors is generated by a code developed for this thesis titled Trajectories for Heavy-lift Evaluation and Optimization (THEO). THEO is a validated trajectory simulation code with the ability to model numerous launch configurations. THEO also has the capability to provide the means for an optimization objective. Optimization of a launch vehicle can be specified in terms of many different variables. For a heavy lift launch vehicle in this thesis, the goal of optimization is to minimize Gross Lift Off Weight (GLOW). THEO provides the capability to optimize by simulating hundreds of thousands of trajectories for a single configuration through the variation of preset independent variables. The sheer volume of these trajectories provides the means to locate configurations that minimize GLOW. Optimization can also be performed by determining the minimum amount of energy necessary to reach target burnout conditions. The energy requirements are then correlated to the propellant mass which can be used to estimate GLOW. This thesis first discusses the validation of THEO as a simulation program and the properties associated with accurately modeling a trajectory. It then relates how THEO and other developed tools can be utilized to determine a configuration that is optimized to minimize GLOW to orbit for adaptable payload sizes

Breakdown of atomic hyperfine coupling in a deep optical-dipole trap

We experimentally study the breakdown of hyperfine coupling for an atom in a deep optical-dipole trap. One-color laser spectroscopy is performed at the resonance lines of a single $^{87}$Rb atom for a trap wavelength of 1064 nm. Evidence of hyperfine breakdown comes from three observations, namely a nonlinear dependence of the transition frequencies on the trap intensity, a splitting of lines which are degenerate for small intensities, and the ability to drive transitions which would be forbidden by selection rules in the absence of hyperfine breakdown. From the data, we infer the hyperfine interval of the $5P_{1/2}$ state and the scalar and tensor polarizabilities for the $5P_{3/2}$ state

Increased Dimensionality of Raman Cooling in a Slightly Nonorthogonal Optical Lattice

We experimentally study the effect of a slight nonorthogonality in a two-dimensional optical lattice onto resolved-sideband Raman cooling. We find that when the trap frequencies of the two lattice directions are equal, the trap frequencies of the combined potential exhibit an avoided crossing and the corresponding eigenmodes are rotated by 45 degrees relative to the lattice beams. Hence, tuning the trap frequencies makes it possible to rotate the eigenmodes such that both eigenmodes have a large projection onto any desired direction in the lattice plane, in particular, onto the direction along which Raman cooling works. Using this, we achieve two-dimensional Raman ground-state cooling in a geometry where this would be impossible, if the eigenmodes were not rotated. Our experiment is performed with a single atom inside an optical resonator but this is inessential and the scheme is expected to work equally well in other situations

Generation of single photons from an atom-cavity system

A single rubidium atom trapped within a high-finesse optical cavity is an efficient source of single photons. We theoretically and experimentally study single-photon generation using a vacuum stimulated Raman adiabatic passage. We experimentally achieve photon generation efficiencies of up to 34% and 56% on the D1 and D2 line, respectively. Output coupling with 89% results in record-high efficiencies for single photons in one spatiotemporally well-defined propagating mode. We demonstrate that the observed generation efficiencies are constant in a wide range of applied pump laser powers and virtual level detunings. This allows for independent control over the frequency and wave packet envelope of the photons without loss in efficiency. In combination with the long trapping time of the atom in the cavity, our system constitutes a significant advancement toward an on-demand, highly efficient single-photon source for quantum information processing tasks.Comment: 7 pages, 5 figure

Irradiation-driven mass transfer cycles in compact binaries

We elaborate on the analytical model of Ritter, Zhang, and Kolb (2000, A&A 360, 959) which describes the basic physics of irradiation-driven mass transfer cycles in semi-detached compact binary systems. In particular, we take into account a contribution to the thermal relaxation of the donor star which is unrelated to irradiation and which was neglected in previous studies. We present results of simulations of the evolution of compact binaries undergoing mass transfer cycles, in particular also of systems with a nuclear evolved donor star. These computations have been carried out with a stellar evolution code which computes mass transfer implicitly and models irradiation of the donor star in a point source approximation, thereby allowing for more realistic simulations than were hitherto possible. We find that low-mass X-ray binaries and cataclysmic variables with orbital periods less than about 6 hours can undergo mass transfer cycles only for low angular momentum loss rates. CVs containing a giant donor or one near the terminal age main sequence are more stable than previously thought, but can possibly also undergo mass transfer cycles.Comment: 6 pages, LaTeX, one eps figure, requires asp2004.sty, to appear in: The Astrophysics of Cataclysmic Variables and Related Objects, ASP Conf. Ser., Vol. ?, 2005, J.M. Hameury and J.P. Lasota (eds.

ZTBus: A Dataset of 1000+ Complete, Second-Resolved Driving Missions of Inner-City Transit Buses

This paper presents the Zurich Transit Bus (ZTBus) dataset, which consists of data recorded during driving missions of electric city buses in Zurich, Switzerland. The data was collected over several years on two trolley buses as part of multiple research projects. It involves more than a thousand missions across all seasons, each mission usually covering a full day of operation. The ZTBus dataset contains detailed information on the vehicle's power demand, propulsion system, odometry, global position, ambient temperature, door openings, number of passengers, dispatch patterns within the public transportation network, etc. All signals are synchronized in time and include an absolute timestamp in tabular form. The dataset can be used as a foundation for a variety of studies and analyses. For example, the data can serve as a basis for simulations to estimate the performance of different public transit vehicle types, or to evaluate and optimize control strategies of hybrid electric vehicles. Furthermore, numerous influencing factors on vehicle operation, such as traffic, passenger volume, etc., can be analyzed in detail.Comment: This work has been submitted to Scientific Data for possible publicatio