Distinguishability of hyperentangled Bell state by linear evolution and local projective measurement. (arXiv:1109.1584v1 [quant-ph])

Measuring an entangled state of two particles is crucial to many quantum
communication protocols. Yet Bell state distinguishability using a finite
apparatus obeying linear evolution and local measurement is theoretically
limited. We extend known bounds for Bell-state distinguishability in one and
two variables to the general case of entanglement in $ n$ two-state variables.
We show that at most $ 2^{n+1}-1$ classes out of $ 4^n$ hyper-Bell states can be
distinguished with one copy of the input state. With two copies, complete
distinguishability is possible. We present optimal schemes in each case.

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Encoded Universality of Quantum Computations on the Multi-Atomic Ensembles in the QED Cavity. (arXiv:1109.0291v1 [quant-ph])

We propose an effective set of elementary quantum gates which provide an
encoded universality and demonstrate the physical feasibility of these gates
for the solid-state quantum computer based on the multi-atomic systems in the
QED cavity. We use the two-qubit encoding and swapping-based operations to
simplify a physical realization of universal quantum computing and add the
immunity to a number of errors. This approach allows to implement any encoded
single-qubit operation by three elementary gates and the encoded controlled-
NOT operation can be performed in a single step. The considerable advantages
are also shown for implementing some commonly used controlled gates.

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On the similarity of Sturm-Liouville operators with non-Hermitian boundary conditions to self-adjoint and normal operators. (arXiv:1108.4946v1 [math.SP])

We consider one-dimensional Schroedinger-type operators in a bounded interval
with non-self-adjoint Robin-type boundary conditions. It is well known that
such operators are generically conjugate to normal operators via a similarity
transformation. Motivated by recent interests in quasi-Hermitian Hamiltonians
in quantum mechanics, we study properties of the transformations in detail. We
show that they can be expressed as the sum of the identity and an integral
Hilbert-Schmidt operator. In the case of parity and time reversal boundary
conditions, we establish closed integral-type formulae for the similarity
transformations, derive the similar self-adjoint operator and also find the
associated “charge conjugation” operator, which plays the role of fundamental
symmetry in a Krein-space reformulation of the problem.

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Quantum rate distortion, reverse Shannon theorems, and source-channel separation. (arXiv:1108.4940v1 [quant-ph])

We derive quantum counterparts of two key theorems of classical information
theory, namely, the rate distortion theorem and the source-channel separation
theorem. The rate-distortion theorem gives the ultimate limits on lossy data
compression, and the source-channel separation theorem implies that a two-stage
protocol consisting of compression and channel coding is optimal for
transmitting a memoryless source over a memoryless channel. In spite of their
importance in the classical domain, there has been surprisingly little work in
these areas for quantum information theory. In the present work, we prove that
the quantum rate distortion function is given in terms of the regularized
entanglement of purification. Although this formula is regularized, at the very
least it demonstrates that Barnum’s conjecture on the achievability of the
coherent information for quantum rate distortion is generally false. We also
determine single-letter expressions for entanglement-assisted quantum rate
distortion. Moreover, we prove several quantum source-channel separation
theorems. The strongest of these are in the entanglement-assisted setting, in
which we establish a necessary and sufficient codition for transmitting a
memoryless source over a memoryless quantum channel up to a given distortion.

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Entanglement Dynamics between Inertial and Non-uniformly Accelerated Detectors. (arXiv:1108.3377v1 [gr-qc])

We study how the correlators of two Unruh-DeWitt detectors change in time,
with one detector at rest in a Minkowski frame, the other accelerated
non-uniformly in some specified way, mediated by a scalar quantum field without
direct interaction. The primary challenge in problems of this sort arises from
the fact that an event horizon is absent and Unruh temperature is ill-defined.
By numerical calculation we demonstrate that the response of the accelerated
detector, assuming that the back reaction from the detectors to the field is
negligible, behaves like an oscillator in a bath of time-varying “temperature”
proportional to the instantaneous proper acceleration of the detector, with
oscillatory modifications due to non-adiabatic effects. We then calculate the
evolution of quantum entanglement between the two detectors in Minkowski time
in the weak-coupling regime without mutual influences. In this setup the
acceleration of the detector in effect slows down the disentanglement process
in Minkowski time due to time dilation in that moving detector.

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Current-Controlled Negative Differential Resistance due to Joule Heating in TiO2. (arXiv:1108.3120v1 [cond-mat.mes-hall])

We show that Joule heating causes current-controlled negative differential
resistance (CC-NDR) in TiO2 by constructing an analytical model of the
voltage-current V(I) characteristic based on polaronic transport for Ohm’s Law
and Newton’s Law of Cooling, and fitting this model to experimental data. This
threshold switching is the ‘soft breakdown’ observed during electroforming of
TiO2 and other transition-metal-oxide based memristors, as well as a precursor
to ‘ON’ or ‘SET’ switching of unipolar memristors from their high to their low
resistance states. The shape of the V(I) curve is a sensitive indicator of the
nature of the polaronic conduction.

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How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problem. (arXiv:1108.3080v1 [hep-th])

We analyze cosmology assuming unitary quantum mechanics, using a tripartite
partition into system, observer and environment degrees of freedom. This
generalizes the second law of thermodynamics to “The system’s entropy can’t
decrease unless it interacts with the observer, and it can’t increase unless it
interacts with the environment.” We show that because of the long-range
entanglement created by cosmological inflation, the cosmic entropy decreases
exponentially rather than linearly with the number of bits of information
observed, so that a given observer can reduce entropy by much more than the
amount of information her brain can store. Indeed, we argue that as long as
inflation has occurred in a non-neglible fraction of the volume, almost all
sentient observers will find themselves in a post-inflationary low-entropy
Hubble volume, and we humans have no reason to be surprised that we do as well,
which solves the so-called inflationary entropy problem. An arguably worse
problem for unitary cosmology involves gamma-ray-burst constraints on the “Big
Snap”, a fourth cosmic doomsday scenario alongside the “Big Crunch”, “Big
Chill” and “Big Rip”, where an increasingly granular nature of expanding space
modifies our life-supporting laws of physics.

Our tripartite framework also clarifies when it is valid to make the popular
quantum gravity approximation that the Einstein tensor equals the quantum
expectation value of the stress-energy tensor, and how problems with recent
attempts to explain dark energy as gravitational backreaction from
super-horizon scale fluctuations can be understood as a failure of this
approximation.

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Quantum correlations in the thermodynamic limit: the XY-model. (arXiv:1108.2285v1 [quant-ph])

We investigate thermal properties of quantum correlations in the
thermodynamic limit with reference to the XY-model

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Bell argument: Locality or Realism? Time to make the choice. (arXiv:1108.0001v1 [quant-ph])

We discuss a possibility of resolution nonobjectivity-nonlocality dilemma in
the light of experimental tests of the Bell inequality for two entangled
photons and Bell-like inequality for a single neutron. Our conclusion is that
on the basis of these experiments we can conclude that quantum mechanics is
nonobjective, i.e., values of physical observables cannot be assigned to a
system before measurement. The Bell’s assumption of nonlocality has to be
rejected as having no direct experimental confirmation.

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Resonances for symmetric two-barrier potentials. (arXiv:1107.4092v1 [quant-ph])

We describe a method for the accurate calculation of bound-state and
resonance energies for one-dimensional potentials. We calculate the shape
resonances for symmetric two-barrier potentials and compare them with those
coming from the Siegert approximation, the complex scaling method and the
box-stabilization method. The agreement between the Breit-Wigner profile and
the transmission coefficient about its maximum is more accurate the sharper the
resonance.

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