41,731 research outputs found
Characterization and quantification of symmetric Gaussian state entanglement through a local classicality criterion
A necessary and sufficient condition for characterization and quantification
of entanglement of any bipartite Gaussian state belonging to a special symmetry
class is given in terms of classicality measures of one-party states. For
Gaussian states whose local covariance matrices have equal determinants it is
shown that separability of a two-party state and classicality of one party
state are completely equivalent to each other under a nonlocal operation,
allowing entanglement features to be understood in terms of any available
classicality measure.Comment: 5 pages, 1 figure. Replaced with final published versio
Vortes solutions in nonabelian Higgs theories
A new class of vortex solutions is found in SU(2) gauge theories with two
adjoint representation Higgs bosons. Implications of these new solutions and
their possible connection with Center Gauge fixed pure gauge theories are
discussed.Comment: 8 pages, added references, other changes, including title and
abstrac
On the P-representable subset of all bipartite Gaussian separable states
P-representability is a necessary and sufficient condition for separability
of bipartite Gaussian states only for the special subset of states whose
covariance matrix are locally invariant. Although this
special class of states can be reached by a convenient
transformation over an arbitrary covariance matrix, it represents a loss of
generality, avoiding inference of many general aspects of separability of
bipartite Gaussian states.Comment: Final version with new results added. Slightly more detailed than the
accepted manuscript (to appear in Phys. Rev. A
Fermions in spherical field theory
We derive the spherical field formalism for fermions. We find that the
spherical field method is free from certain difficulties which complicate
lattice calculations, such as fermion doubling, missing axial anomalies, and
computational problems regarding internal fermion loops.Comment: corrected journal inf
Towards Very Large Aperture Massive MIMO: a measurement based study
Massive MIMO is a new technique for wireless communications that claims to
offer very high system throughput and energy efficiency in multi-user
scenarios. The cost is to add a very large number of antennas at the base
station. Theoretical research has probed these benefits, but very few
measurements have showed the potential of Massive MIMO in practice. We
investigate the properties of measured Massive MIMO channels in a large indoor
venue. We describe a measurement campaign using 3 arrays having different shape
and aperture, with 64 antennas and 8 users with 2 antennas each. We focus on
the impact of the array aperture which is the main limiting factor in the
degrees of freedom available in the multiple antenna channel. We find that
performance is improved as the aperture increases, with an impact mostly
visible in crowded scenarios where the users are closely spaced. We also test
MIMO capability within a same user device with user proximity effect. We see a
good channel resolvability with confirmation of the strong effect of the user
hand grip. At last, we highlight that propagation conditions where
line-of-sight is dominant can be favorable
Reversible Pebbling Game for Quantum Memory Management
Quantum memory management is becoming a pressing problem, especially given
the recent research effort to develop new and more complex quantum algorithms.
The only existing automatic method for quantum states clean-up relies on the
availability of many extra resources. In this work, we propose an automatic
tool for quantum memory management. We show how this problem exactly matches
the reversible pebbling game. Based on that, we develop a SAT-based algorithm
that returns a valid clean-up strategy, taking the limitations of the quantum
hardware into account. The developed tool empowers the designer with the
flexibility required to explore the trade-off between memory resources and
number of operations. We present three show-cases to prove the validity of our
approach. First, we apply the algorithm to straight-line programs, widely used
in cryptographic applications. Second, we perform a comparison with the
existing approach, showing an average improvement of 52.77%. Finally, we show
the advantage of using the tool when synthesizing a quantum circuit on a
constrained near-term quantum device.Comment: In Proc. Design Automation and Test in Europe (DATE 2019
Phase motion in the amplitude in decay
In view of the proliferation in the number of new charmonium states, it is
really important to have a experimental way to prove that an observed bump is,
indeed, a real resonance. To do that, in this paper we present an alternative
method to demonstrate the resonant behavior of a state. With this method, the
phase variation of a generic complex amplitude can be directly revealed through
interference in the Dalitz-plot region where it crosses a well established
resonant state, used as a probe. We have tested the method for the
state by generating Monte Carlo samples for the
decay channel. We have shown that the proposed method gives a clear oscillation
behavior, related to the phase variation associated to a real resonant state,
in the case where the is considered as a regular resonance with a
strong phase variation. We have also discussed the possibility of using the
proposed method complementary to the Argand diagram to determine the internal
structure of the state.Comment: 6 pages, 2 figures -- submitted to Phys. Lett.
Noisy One-Way Quantum Computations: The Role of Correlations
A scheme to evaluate computation fidelities within the one-way model is
developed and explored to understand the role of correlations in the quality of
noisy quantum computations. The formalism is promptly applied to many
computation instances, and unveils that a higher amount of entanglement in the
noisy resource state does not necessarily imply a better computation.Comment: 10 pages, 6 figures, extension of a previous versio
Entanglement versus mixedness for coupled qubits under a phase damping channel
Quantification of entanglement against mixing is given for a system of
coupled qubits under a phase damping channel. A family of pure initial joint
states is defined, ranging from pure separable states to maximally entangled
state. An ordering of entanglement measures is given for well defined initial
state amount of entanglement.Comment: 9 pages, 2 figures. Replaced with final published versio
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