5,309 research outputs found
Model tests of cluster separability in relativistic quantum mechanics
A relativistically invariant quantum theory first advanced by Bakamjian and
Thomas has proven very useful in modeling few-body systems. For three particles
or more, this approach is known formally to fail the constraint of cluster
separability, whereby symmetries and conservation laws that hold for a system
of particles also hold for isolated subsystems. Cluster separability can be
restored by means of a recursive construction using unitary transformations,
but implementation is difficult in practice, and the quantitative extent to
which the Bakamjian-Thomas approach violates cluster separability has never
been tested. This paper provides such a test by means of a model of a scalar
probe in a three-particle system for which (1) it is simple enough that there
is a straightforward solution that satisfies Poincar\'e invariance and cluster
separability, and (2) one can also apply the Bakamjian-Thomas approach. The
difference between these calculations provides a measure of the size of the
corrections from the Sokolov construction that are needed to restore cluster
properties. Our estimates suggest that, in models based on nucleon degrees of
freedom, the corrections that restore cluster properties are too small to
effect calculations of observables.Comment: 13 pages, 15 figure
A quantum volume hologram
We propose a new scheme for parallel spatially multimode quantum memory for
light. The scheme is based on counter-propagating quantum signal wave and
strong classical reference wave, like in a classical volume hologram, and
therefore can be called a quantum volume hologram. The medium for the hologram
consists of a spatially extended ensemble of atoms placed in a magnetic field.
The write-in and read-out of this quantum hologram is as simple as that of its
classical counterpart and consists of a single pass illumination. In addition
we show that the present scheme for a quantum hologram is less sensitive to
diffraction and therefore is capable of achieving higher density of storage of
spatial modes as compared to previous proposals. A quantum hologram capable of
storing entangled images can become an important ingredient in quantum
information processing and quantum imaging.Comment: 8 pages, 2 figure
Thermally activated breakdown in a simple polymer model
We consider the thermally activated fragmentation of a homopolymer chain. In
our simple model the dynamics of the intact chain is a Rouse one until a bond
breaks and bond breakdown is considered as a first passage problem over a
barrier to an absorbing boundary. Using the framework of the Wilemski-Fixman
approximation we calculate activation times of individual bonds for free and
grafted chains. We show that these times crucially depend on the length of the
chain and the location of the bond yielding a minimum at the free chain ends.
Theoretical findings are qualitatively confirmed by Brownian dynamics
simulations
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