2,764 research outputs found

    Explicit product ensembles for separable quantum states

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    We present a general method for constructing pure-product-state representations for density operators of NN quantum bits. If such a representation has nonnegative expansion coefficients, it provides an explicit separable ensemble for the density operator. We derive the condition for separability of a mixture of the Greenberger-Horne-Zeilinger state with the maximally mixed state.Comment: 15 pages, no figure

    Thermodynamics and kinetics of pack aluminide coating formation on IN-100

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    An investigation of the effects of pack variables on the formation of aluminide coatings on nickel-base superalloy IN-100 was conducted. Also, the thermodynamics and kinetics of coating formation were analyzed. Observed coating weights were in good agreement with predictions made from the analysis. Pack temperature rather than pack aluminum activity controls the principal coating phase formed. In 1 weight percent aluminum packs, aluminum weight gains were related to the halide pack activator. Solid-state nickel diffusion controlled coating formation from sodium fluoride and chloride and ammonium fluoride activated packs. In other ammonium and sodium halide activated 1 weight percent aluminum packs, gaseous diffusion controlled coating formation

    Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic

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    Four-wave mixing near resonance in an atomic vapor can produce relative intensity squeezed light suitable for precision measurements beyond the shot-noise limit. We develop an analytic distributed gain/loss model to describe the competition of mixing and absorption through the non-linear medium. Using a novel matrix calculus, we present closed-form expressions for the degree of relative intensity squeezing produced by this system. We use these theoretical results to analyze experimentally measured squeezing from a 85^{85}Rb vapor and demonstrate the analytic model's utility as an experimental diagnostic.Comment: 10 pages, 5 figure

    A two-step MaxLik-MaxEnt strategy to infer photon distribution from on/off measurement at low quantum efficiency

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    A method based on Maximum-Entropy (ME) principle to infer photon distribution from on/off measurements performed with few and low values of quantum efficiency is addressed. The method consists of two steps: at first some moments of the photon distribution are retrieved from on/off statistics using Maximum-Likelihood estimation, then ME principle is applied to infer the quantum state and, in turn, the photon distribution. Results from simulated experiments on coherent and number states are presented.Comment: 4 figures, to appear in EPJ

    Hypersensitivity to Perturbations in the Quantum Baker's Map

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    We analyze a randomly perturbed quantum version of the baker's transformation, a prototype of an area-conserving chaotic map. By numerically simulating the perturbed evolution, we estimate the information needed to follow a perturbed Hilbert-space vector in time. We find that the Landauer erasure cost associated with this information grows very rapidly and becomes much larger than the maximum statistical entropy given by the logarithm of the dimension of Hilbert space. The quantum baker's map thus displays a hypersensitivity to perturbations that is analogous to behavior found earlier in the classical case. This hypersensitivity characterizes ``quantum chaos'' in a way that is directly relevant to statistical physics.Comment: 8 pages, LATEX, 3 Postscript figures appended as uuencoded fil

    Hydrogen-atmosphere induction furnace has increased temperature range

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    Improved hydrogen-atmosphere induction furnace operates at temperatures up to 5,350 deg F. The furnace heats up from room temperature to 4,750 deg F in 30 seconds and cools down to room temperature in 2 minutes

    Standard Quantum Limits for broadband position measurement

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    I utilize the Caves-Milburn model for continuous position measurements to formulate a broadband version of the Standard Quantum Limit (SQL) for monitoring the position of a free mass, and illustrate the use of Kalman filtering to recover the SQL for estimating a weak classical force that acts on a quantum-mechanical test particle under continuous observation. These derivations are intended to clarify the interpretation of SQL's in the context of continuous quantum measurement.Comment: Replaced version: changed title, fixed algebra error at the very end, conclusions modified accordingly. Four pages, one eps figur

    New Photodetection Method Using Unbalanced Sidebands for Squeezed Quantum Noise in Gravitational Wave Interferometer

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    Homodyne detection is one of the ways to circumvent the standard quantum limit for a gravitational wave detector. In this paper it will be shown that the same quantum-non-demolition effect using homodyne detection can be realized by heterodyne detection with unbalanced RF sidebands. Furthermore, a broadband quantum-non-demolition readout scheme can also be realized by the unbalanced sideband detection.Comment: 9 pages, 5 figure
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