1,893 research outputs found
Center of Mass and spin for isolated sources of gravitational radiation
We define the center of mass and spin of an isolated system in General
Relativity. The resulting relationships between these variables and the total
linear and angular momentum of the gravitational system are remarkably similar
to their Newtonian counterparts, though only variables at the null boundary of
an asymptotically flat spacetime are used for their definition. We also derive
equations of motion linking their time evolution to the emitted gravitational
radiation. The results are then compared to other approaches. In particular one
obtains unexpected similarities as well as some differences with results
obtained in the Post Newtonian literature . These equations of motion should be
useful when describing the radiation emitted by compact sources such as
coalescing binaries capable of producing gravitational kicks, supernovas, or
scattering of compact objects.Comment: 16 pages. Accepted for publication in Phys. Rev.
A non-Markovian optical signature for detecting entanglement in coupled excitonic qubits
We identify an optical signature for detecting entanglement in experimental
nanostructure systems comprising coupled excitonic qubits. This signature owes
its strength to non-Markovian dynamical effects in the second-order temporal
coherence function of the emitted radiation. We calculate autocorrelation and
cross-correlation functions for both selective and collective light excitation,
and prove that the coherence properties of the emitted light do indeed carry
information about the entanglement of the initial multi-qubit state.
We also show that this signature can survive in the presence of a noisy
environment.Comment: 4 pages, 4 color figures. Minor changes. Accepted version to be
published in Europhysics Letter
Ultrafast optical signature of quantum superpositions in a nanostructure
We propose an unambiguous signature for detecting quantum superposition
states in a nanostructure, based on current ultrafast spectroscopy techniques.
The reliable generation of such superposition states via Hadamard-like quantum
gates is crucial for implementing solid-state based quantum information
schemes. The signature originates from a remarkably strong photon antibunching
effect which is enhanced by non-Markovian dynamics.Comment: 4 pages, 2 figures. Published in Phys. Rev. B (Rapid Communications
New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions
We reveal universal dynamical scaling behavior across adiabatic quantum phase
transitions (QPTs) in networks ranging from traditional spatial systems (Ising
model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our
findings, which lie beyond traditional critical exponent analysis and adiabatic
perturbation approximations, are applicable even where excitations have not yet
stabilized and hence provide a time-resolved understanding of QPTs encompassing
a wide range of adiabatic regimes. We show explicitly that even though two
systems may traditionally belong to the same universality class, they can have
very different adiabatic evolutions. This implies more stringent conditions
need to be imposed than at present, both for quantum simulations where one
system is used to simulate the other, and for adiabatic quantum computing
schemes.Comment: 5 pages, 3 figures, plus supplementary material (6 pages, 1 figure
Nonequilibrium dynamics of polariton entanglement in a cluster of coupled traps
We study in detail the generation and relaxation of quantum coherences
(entanglement) in a system of coupled polariton traps. By exploiting a Lie
algebraic based super-operator technique we provide an analytical exact
solution for the Markovian dissipative dynamics (Master equation) of such
system which is valid for arbitrary cluster size, polariton-polariton
interaction strength, temperature and initial state. Based on the exact
solution of the Master equation at T=0K, we discuss how dissipation affects the
quantum entanglement dynamics of coupled polariton systems.Comment: 5 pages, 2 figures, SLAFES XIX contribution pape
Large dynamic light-matter entanglement from driving neither too fast nor too slow
A significant problem facing next-generation quantum technologies is how to
generate and manipulate macroscopic entanglement in light and matter systems.
Here we report a new regime of dynamical light-matter behavior in which a
giant, system-wide entanglement is generated by varying the light-matter
coupling at \emph{intermediate} velocities. This enhancement is far larger and
broader-ranged than that occurring near the quantum phase transition of the
same model under adiabatic conditions. By appropriate choices of the coupling
within this intermediate regime, the enhanced entanglement can be made to
spread system-wide or to reside in each subsystem separately.Comment: 7 pages, 7 figure
Direct equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems: scaling of entanglement
We show that the quantum phase transition arising in a standard
radiation-matter model (Dicke model) belongs to the same universality class as
the infinitely-coordinated, transverse field XY model. The effective
qubit-qubit exchange interaction is shown to be proportional to the square of
the qubit-radiation coupling. A universal finite-size scaling is derived for
the corresponding two-qubit entanglement (concurrence) and a size-consistent
effective Hamiltonian is proposed for the qubit subsystem.Comment: 4 pages, 3 figures. Minor changes. Published versio
Robust quantum correlations in out-of-equilibrium matter-light systems
High precision macroscopic quantum control in interacting light-matter
systems remains a significant goal toward novel information processing and
ultra-precise metrology. We show that the out-of-equilibrium behavior of a
paradigmatic light-matter system (Dicke model) reveals two successive stages of
enhanced quantum correlations beyond the traditional schemes of near-adiabatic
and sudden quenches. The first stage features magnification of matter-only and
light-only entanglement and squeezing due to effective non-linear
self-interactions. The second stage results from a highly entangled
light-matter state, with enhanced superradiance and signatures of chaotic and
highly quantum states. We show that these new effects scale up consistently
with matter system size, and are reliable even in dissipative environments.Comment: 14 pages, 6 figure
Vanishing Cosmological Constant in Modified Gauss-Bonnet Gravity with Conformal Anomaly
We consider dark energy cosmology in a de Sitter universe filled with quantum
conformal matter. Our model represents a Gauss-Bonnet model of gravity with
contributions from quantum effects. To the General Relativity action an
arbitrary function of the GB invariant, f(G), is added, and taking into account
quantum effects from matter the cosmological constant is studied. For the
considered model the conditions for a vanishing cosmological constant are
considered. Creation of a de Sitter universe by quantum effects in a GB
modified gravity is discussed.Comment: 8 pages latex, 1 figure. To appear in Int. J. Mod. Phys.
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