16,941 research outputs found
Implications of Lorentz covariance for the guidance equation in two-slit quantum interference
It is known that Lorentz covariance fixes uniquely the current and the
associated guidance law in the trajectory interpretation of quantum mechanics
for spin particles. In the non-relativistic domain this implies a guidance law
for the electron which differs by an additional spin-dependent term from that
originally proposed by de Broglie and Bohm. In this paper we explore some of
the implications of the modified guidance law. We bring out a property of
mutual dependence in the particle coordinates that arises in product states,
and show that the quantum potential has scalar and vector components which
implies the particle is subject to a Lorentz-like force. The conditions for the
classical limit and the limit of negligible spin are given, and the empirical
sufficiency of the model is demonstrated. We then present a series of
calculations of the trajectories based on two-dimensional Gaussian wave packets
which illustrate how the additional spin-dependent term plays a significant
role in structuring both the individual trajectories and the ensemble. The
single packet corresponds to quantum inertial motion. The distinct features
encountered when the wavefunction is a product or a superposition are explored,
and the trajectories that model the two-slit experiment are given. The latter
paths exhibit several new characteristics compared with the original de
Broglie-Bohm ones, such as crossing of the axis of symmetry.Comment: 27 pages including 6 pages of figure
Entangled-state cryptographic protocol that remains secure even if nonlocal hidden variables exist and can be measured with arbitrary precision
Standard quantum cryptographic protocols are not secure if one assumes that
nonlocal hidden variables exist and can be measured with arbitrary precision.
The security can be restored if one of the communicating parties randomly
switches between two standard protocols.Comment: Shortened version, accepted in Phys. Rev.
Dynamics of spin 1/2 quantum plasmas
The fully nonlinear governing equations for spin 1/2 quantum plasmas are
presented. Starting from the Pauli equation, the relevant plasma equations are
derived, and it is shown that nontrivial quantum spin couplings arise, enabling
studies of the combined collective and spin dynamics. The linear response of
the quantum plasma in an electron--ion system is obtained and analyzed.
Applications of the theory to solid state and astrophysical systems as well as
dusty plasmas are pointed out.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
EMCCDs for space applications
This paper describes a qualification programme for Electron-Multiplication Charge Coupled Devices (EMCCDs) for use in space applications. While the presented results are generally applicable, the programme was carried out in the context of CCD development for the Radial Velocity Spectrometer (RVS) instrument on the European Space Agency's cornerstone Gaia mission. We discuss the issues of device radiation tolerance, charge transfer efficiency at low signal levels and life time effects on the electron-multiplication gain. The development of EMCCD technology to allow operation at longer wavelengths using high resistivity silicon, and the cryogenic characterisation of EMCCDs are also described
Relativistic quantum mechanics and the Bohmian interpretation
Conventional relativistic quantum mechanics, based on the Klein-Gordon
equation, does not possess a natural probabilistic interpretation in
configuration space. The Bohmian interpretation, in which probabilities play a
secondary role, provides a viable interpretation of relativistic quantum
mechanics. We formulate the Bohmian interpretation of many-particle wave
functions in a Lorentz-covariant way. In contrast with the nonrelativistic
case, the relativistic Bohmian interpretation may lead to measurable
predictions on particle positions even when the conventional interpretation
does not lead to such predictions.Comment: 10 pages, revised, to appear in Found. Phys. Let
Importance of charge capture in interphase regions during readout of charge-coupled devices
The current understanding of charge transfer dynamics in charge-coupled devices (CCDs) is that charge is moved so quickly from one phase to the next in a clocking sequence and with a density so low that trapping of charge in the interphase regions is negligible. However, simulation capabilities developed at the Centre for Electronic Imaging, which includes direct input of electron density simulations, have made it possible to investigate this assumption further. As part of the radiation testing campaign of the Euclid CCD273 devices, data have been obtained using the trap pumping method, a method that can be used to identify and characterize single defects within CCDs. Combining these data with simulations, we find that trapping during the transfer of charge among phases is indeed necessary to explain the results of the data analysis. This result could influence not only trap pumping theory and how trap pumping should be performed but also how a radiation-damaged CCD is readout in the most optimal way
Quantum Kinetic Theory III: Simulation of the Quantum Boltzmann Master Equation
We present results of simulations of a em quantum Boltzmann master equation
(QBME) describing the kinetics of a dilute Bose gas confined in a trapping
potential in the regime of Bose condensation. The QBME is the simplest version
of a quantum kinetic master equations derived in previous work. We consider two
cases of trapping potentials: a 3D square well potential with periodic boundary
conditions, and an isotropic harmonic oscillator. We discuss the stationary
solutions and relaxation to equilibrium. In particular, we calculate particle
distribution functions, fluctuations in the occupation numbers, the time
between collisions, and the mean occupation numbers of the one-particle states
in the regime of onset of Bose condensation.Comment: 12 pages, 15 figure
Vortex interaction, chaos and quantum probabilities
The motion of a single vortex is able to originate chaos in the quantum
trajectories defined in Bohm's interpretation of quantum mechanics. In this
Letter, we show that this is also the case in the general situation, in which
many interacting vortices exist. This result gives support to recent attempts
in which Born's probability rule is derived in terms of an irreversible time
evolution to equilibrium, rather than being postulated.Comment: 4 pages, 4 figure
Discontinuous Percolation Transitions in Epidemic Processes, Surface Depinning in Random Media and Hamiltonian Random Graphs
Discontinuous percolation transitions and the associated tricritical points
are manifest in a wide range of both equilibrium and non-equilibrium
cooperative phenomena. To demonstrate this, we present and relate the
continuous and first order behaviors in two different classes of models: The
first are generalized epidemic processes (GEP) that describe in their spatially
embedded version - either on or off a regular lattice - compact or fractal
cluster growth in random media at zero temperature. A random graph version of
GEP is mapped onto a model previously proposed for complex social contagion. We
compute detailed phase diagrams and compare our numerical results at the
tricritical point in d = 3 with field theory predictions of Janssen et al.
[Phys. Rev. E 70, 026114 (2004)]. The second class consists of exponential
("Hamiltonian", or formally equilibrium) random graph models and includes the
Strauss and the 2-star model, where 'chemical potentials' control the densities
of links, triangles or 2-stars. When the chemical potentials in either graph
model are O(logN), the percolation transition can coincide with a first order
phase transition in the density of links, making the former also discontinuous.
Hysteresis loops can then be of mixed order, with second order behavior for
decreasing link fugacity, and a jump (first order) when it increases
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