677 research outputs found
On the Relation Between Quantum Mechanical and Classical Parallel Transport
We explain how the kind of ``parallel transport'' of a wavefunction used in
discussing the Berry or Geometrical phase induces the conventional parallel
transport of certain real vectors. These real vectors are associated with
operators whose commutators yield diagonal operators; or in Lie algebras those
operators whose commutators are in the (diagonal) Cartan subalgebra.Comment: 3 pages, no figure
Investigation of electrochemical behavior of plasma nitrided Ti-6Al-7Nb alloy in Hanks’ Solution
Titanium alloy Ti-6Al-7Nb was plasma nitrided using inductively coupled RF Plasma with 100% Nitrogen at 750, 800 and 850°C for 4 h. Micro Raman studies show the formation of titanium nitrides. Potentiodynamic polarization studies in Hanks’ solution show the corrosion resistance of the untreated samples to be better than the treated samples. Electrochemical Impedance Spectroscopy (EIS) studies show higher charge transfer resistance and lower double layer capacitance for the substrate compared to the nitrided samples. FESEM images of samples immersed in SBF show that growth of apatite is more and the size of deposits are larger on nitrided samples as compared to that on the untreated substrate. Nitrided samples immersed in Hanks’ solution for 7 days show higher amount of calcium, phosphorous and oxygen than the substrate
Geometric phases for mixed states in interferometry
We provide a physical prescription based on interferometry for introducing
the total phase of a mixed state undergoing unitary evolution, which has been
an elusive concept in the past. We define the parallel transport condition that
provides a connection-form for obtaining the geometric phase for mixed states.
The expression for the geometric phase for mixed state reduces to well known
formulas in the pure state case when a system undergoes noncyclic and unitary
quantum evolution.Comment: Two column, 4 pages, Latex file, No figures, Few change
Continuous Time-Dependent Measurements: Quantum Anti-Zeno Paradox with Applications
We derive differential equations for the modified Feynman propagator and for
the density operator describing time-dependent measurements or histories
continuous in time. We obtain an exact series solution and discuss its
applications. Suppose the system is initially in a state with density operator
and the projection operator is measured
continuously from to , where is a projector obeying and a unitary operator obeying and some smoothness
conditions in . Then the probability of always finding from to is unity. Generically and the watched system is sure to
change its state, which is the anti-Zeno paradox noted by us recently. Our
results valid for projectors of arbitrary rank generalize those obtained by
Anandan and Aharonov for projectors of unit rank.Comment: 16 pages, latex; new material and references adde
Reply to `Singularities of the mixed state phase'
The only difference between Bhandari's viewpoint [quant-ph/0108058] and ours
[Phys. Rev. Lett. 85, 2845 (2000)] is that our phase is defined modulo ,
whereas Bhandari argues that two phases that differ by , integer,
may be distinguished experimentally in a history-dependent manner.Comment: 2 page
Model for Entangled States with Spin-Spin Interaction
A system consisting of two neutral spin 1/2 particles is analyzed for two
magnetic field perturbations: 1) an inhomogeneous magnetic field over all
space, and 2) external fields over a half space containing only one of the
particles. The field is chosen to point from one particle to the other, which
results in essentially a one-dimensional problem. A number of interesting
features are revealed for the first case: the singlet, which has zero potential
energy in the unperturbed case, remains unstable in the perturbing field. The
spin zero component of the triplet evolves into a bound state with a double
well potential, with the possibility of tunneling. Superposition states can be
constructed which oscillate between entangled and unentangled states. For the
second case, we show that changes in the magnetic field around one particle
affect measurements of the spin of the entangled particle not in the magnetic
field nonlocally. By using protective measurements, we show it is possible in
principle to establish a nonlocal interaction using the two particles, provided
the dipole-dipole potential energy does not vanish and is comparable to the
potential energy of the particle in the external field
The non-Abelian state-dependent gauge field in optics
The covariant formulation of the quantum dynamics in CP(1) should lead to the
observable geometrodynamical effects for the local dynamical variable of the
light polarization states.Comment: 8 pages, 3 figures, LaTe
On the spin of gravitational bosons
We unearth spacetime structure of massive vector bosons, gravitinos, and
gravitons. While the curvatures associated with these particles carry a
definite spin, the underlying potentials cannot be, and should not be,
interpreted as single spin objects. For instance, we predict that a spin
measurement in the rest frame of a massive gravitino will yield the result 3/2
with probability one half, and 1/2 with probability one half. The simplest
scenario leaves the Riemannian curvature unaltered; thus avoiding conflicts
with classical tests of the theory of general relativity. However, the quantum
structure acquires additional contributions to the propagators, and it gives
rise to additional phases.Comment: Honorable mention, 2002 Gravity Research Foundation Essay
Comments on Proposed Gravitational Modifications of Schrodinger Dynamics and their Experimental Implications
We discuss aspects of gravitational modifications of Schrodinger dynamics
proposed by Diosi and Penrose. We consider first the Diosi-Penrose criterion
for gravitationally induced state vector reduction, and compute the reduction
time expected for a superposition of a uniform density cubical solid in two
positions displaced by a small fraction of the cube side. We show that the
predicted effect is much smaller than would be observable in the proposed
Marshall et al. mirror experiment. We then consider the ``Schrodinger -Newton''
equation for an N-particle system. We show that in the independent particle
approximation, it differs from the usual Hartree approximation applied to the
Newtonian potential by self-interaction terms, which do not have a consistent
Born rule interpretation. This raises doubts about the use of the
Schrodinger-Newton equation to calculate gravitational effects on molecular
interference experiments. When the effects of Newtonian gravitation on
molecular diffraction are calculated using the standard many-body Schrodinger
equation, no washing out of the interference pattern is predicted.Comment: Tex, 17
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