Describing mixed spin-space entanglement of pure states of indistinguishable particles using an occupation number basis

Quantum mechanical entanglement is a resource for quantum computation, quantum teleportation, and quantum cryptography. The ability to quantify this resource correctly has thus become of great interest to those working in the field of quantum information theory. In this paper, we show that all existing entanglement measures but one fail important tests of fitness when applied to n particle, m site states of indistinguishable particles, where n,m>=2. The accepted method of measuring the entanglement of a bipartite system of distinguishable particles is to use the von Neumann entropy of the reduced density matrix of one half of the system. We show that expressing the full density matrix using a site-spin occupation number basis, and reducing with respect to that basis, gives an entanglement which meets all currently known fitness criteria for systems composed of either distinguishable or indistinguishable particles. We consider an output state from a previously published thought experiment, a state which is entangled in both spin and spatial degrees of freedom, and show that the site entropy measure gives the correct total entanglement. We also show how the spin-space entanglement transfer occurring within the apparatus can be understood in terms of the transfer of probability from single-occupancy to double-occupancy sectors of the density matrix.Comment: 2 figures; added Appendix A; added Figure 2; made changes to take account of v2 of quant-ph/0105120; some typos remove

Photon Channelling in Foams

We report on the absorption of diffuse photons in aqueous foams by a dye added to the continuous liquid phase. For very wet and for dry foams, the absorption of the diffuse photons equals the absorption length of the liquid divided by the liquid volume fraction. This indicates that the diffuse photons propagate by a random walk, sampling each phase in proportion to its volume. Foams of intermediate wetness, by contrast, absorb photons more strongly than expected. A 2D computer simulation, modeling photons scattering in a foam crystal, also shows enhanced absorption. This encourages us to consider novel transport effects, such as the total internal reflection of photons inside the Plateau borders

Bi-partite mode entanglement of bosonic condensates on tunneling graph

We study a set of $L$ spatial bosonic modes localized on a graph $\Gamma.$ The particles are allowed to tunnel from vertex to vertex by hopping along the edges of $\Gamma.$ We analyze how, in the exact many-body eigenstates of the system i.e., Bose-Einstein condensates over single-particle eigenfunctions, the bi-partite quantum entanglement of a lattice vertex with respect to the rest of the graph depends on the topology of $\Gamma.$Comment: 3 Pages LaTeX, 2 Figures include

Speckle-visibility spectroscopy: A tool to study time-varying dynamics

We describe a multispeckle dynamic light scattering technique capable of resolving the motion of scattering sites in cases that this motion changes systematically with time. The method is based on the visibility of the speckle pattern formed by the scattered light as detected by a single exposure of a digital camera. Whereas previous multispeckle methods rely on correlations between images, here the connection with scattering site dynamics is made more simply in terms of the variance of intensity among the pixels of the camera for the specified exposure duration. The essence is that the speckle pattern is more visible, i.e. the variance of detected intensity levels is greater, when the dynamics of the scattering site motion is slow compared to the exposure time of the camera. The theory for analyzing the moments of the spatial intensity distribution in terms of the electric field autocorrelation is presented. It is demonstrated for two well-understood samples, a colloidal suspension of Brownian particles and a coarsening foam, where the dynamics can be treated as stationary. However, the method is particularly appropriate for samples in which the dynamics vary with time, either slowly or rapidly, limited only by the exposure time fidelity of the camera. Potential applications range from soft-glassy materials, to granular avalanches, to flowmetry of living tissue.Comment: review - theory and experimen

Laboratory Experiments, Numerical Simulations, and Astronomical Observations of Deflected Supersonic Jets: Application to HH 110

Collimated supersonic flows in laboratory experiments behave in a similar manner to astrophysical jets provided that radiation, viscosity, and thermal conductivity are unimportant in the laboratory jets, and that the experimental and astrophysical jets share similar dimensionless parameters such as the Mach number and the ratio of the density between the jet and the ambient medium. Laboratory jets can be studied for a variety of initial conditions, arbitrary viewing angles, and different times, attributes especially helpful for interpreting astronomical images where the viewing angle and initial conditions are fixed and the time domain is limited. Experiments are also a powerful way to test numerical fluid codes in a parameter range where the codes must perform well. In this paper we combine images from a series of laboratory experiments of deflected supersonic jets with numerical simulations and new spectral observations of an astrophysical example, the young stellar jet HH 110. The experiments provide key insights into how deflected jets evolve in 3-D, particularly within working surfaces where multiple subsonic shells and filaments form, and along the interface where shocked jet material penetrates into and destroys the obstacle along its path. The experiments also underscore the importance of the viewing angle in determining what an observer will see. The simulations match the experiments so well that we can use the simulated velocity maps to compare the dynamics in the experiment with those implied by the astronomical spectra. The experiments support a model where the observed shock structures in HH 110 form as a result of a pulsed driving source rather than from weak shocks that may arise in the supersonic shear layer between the Mach disk and bow shock of the jet's working surface.Comment: Full resolution figures available at http://sparky.rice.edu/~hartigan/pub.html To appear in Ap

Quantifying Entanglement Production of Quantum Operations

The problem of entanglement produced by an arbitrary operator is formulated and a related measure of entanglement production is introduced. This measure of entanglement production satisfies all properties natural for such a characteristic. A particular case is the entanglement produced by a density operator or a density matrix. The suggested measure is valid for operations over pure states as well as over mixed states, for equilibrium as well as nonequilibrium processes. Systems of arbitrary nature can be treated, described either by field operators, spin operators, or any other kind of operators, which is realized by constructing generalized density matrices. The interplay between entanglement production and phase transitions in statistical systems is analysed by the examples of Bose-Einstein condensation, superconducting transition, and magnetic transitions. The relation between the measure of entanglement production and order indices is analysed.Comment: 20 pages, Revte

Swinging open or slamming shut? The implications of China's open-door policy for women, educational choice and work.

This paper explores the link between international tertiary education and evolving attitudes about women and work in China. The paper reviews literature about gender and education in China, commenting on the late-twentieth-century post-reform environment. It goes on to present illustrative primary research material from two studies carried out between 1999 and 2004 with students studying for UK Business degrees in China and the UK. The research data is presented as extracts from oral histories, where participants discuss education and attitudes about work, gender and identity. The main conclusions are that women in post-reform China have been educationally and socially disadvantaged compared to men; traditional gender attitudes about women, work and education persist in contemporary China; women are seeking opportunities in international higher education to overcome domestic prejudices; and degree-educated professional women may be developing as a new social class in contemporary Chinese society