17,520 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.
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
Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A
The first polarimetric images of the OMC-3 region of the Orion A filamentary
molecular cloud are presented. Using the JCMT, we have detected polarized
thermal emission at 850 microns from dust along a 6' length of the dense
filament. The polarization pattern is highly ordered and is aligned with the
filament throughout most of the region. The plane-of-sky magnetic field
direction is perpendicular to the measured polarization. The mean percentage
polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of
the integral-shaped filament, and active star formation is ongoing along its
length. The protostellar outflow directions do not appear to be consistently
correlated with the direction of the plane-of-sky field or the filament
structure itself. Depolarization toward the filament center, previously
detected in many other star-forming cores and protostars, is also evident in
our data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the
March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa
Intensity fluctuations in steady state superradiance
Alkaline-earth like atoms with ultra-narrow optical transitions enable
superradiance in steady state. The emitted light promises to have an
unprecedented stability with a linewidth as narrow as a few millihertz. In
order to evaluate the potential usefulness of this light source as an
ultrastable oscillator in clock and precision metrology applications it is
crucial to understand the noise properties of this device. In this paper we
present a detailed analysis of the intensity fluctuations by means of
Monte-Carlo simulations and semi-classical approximations. We find that the
light exhibits bunching below threshold, is to a good approximation coherent in
the superradiant regime, and is chaotic above the second threshold.Comment: 8 pages, 5 figure
Spin-dependent Bohm trajectories associated with an electronic transition in hydrogen
The Bohm causal theory of quantum mechanics with spin-dependence is used to
determine electron trajectories when a hydrogen atom is subjected to
(semi-classical) radiation. The transition between the 1s ground state and the
2p0 state is examined. It is found that transitions can be identified along
Bohm trajectories. The trajectories lie on invariant hyperboloid surfaces of
revolution in R^3. The energy along the trajectories is also discussed in
relation to the hydrogen energy eigenvalues.Comment: 18 pages, 8 figure
Non-destructive cavity QED probe of Bloch oscillations in a gas of ultracold atoms
We describe a scheme for probing a gas of ultracold atoms trapped in an
optical lattice and moving in the presence of an external potential. The probe
is non-destructive and uses the existing lattice fields as the measurement
device. Two counter-propagating cavity fields simultaneously set up a
conservative lattice potential and a weak quantum probe of the atomic motion.
Balanced heterodyne detection of the probe field at the cavity output along
with integration in time and across the atomic cloud yield information about
the atomic dynamics in a single run. The scheme is applied to a measurement of
the Bloch oscillation frequency for atoms moving in the presence of the local
gravitational potential. Signal-to-noise ratios are estimated to be as high as
.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
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