41 research outputs found
Natural multiparticle entanglement in a Fermi gas
We investigate multipartite entanglement in a non-interacting fermion gas, as
a function of fermion separation, starting from the many particle fermion
density matrix. We prove that all multiparticle entanglement can be built only
out of two-fermion entanglement. Although from the Pauli exclusion principle we
would always expect entanglement to decrease with fermion distance, we
surprisingly find the opposite effect for certain fermion configurations. The
von Neumann entropy is found to be proportional to the volume for a large
number of particles even when they are arbitrarily close to each other. We will
illustrate our results using different configurations of two, three, and four
fermions at zero temperature although all our results can be applied to any
temperature and any number of particles.Comment: Replaced with revised editio
Magnetic Susceptibility as a Macrosopic Entaglement Witness
We show that magnetic susceptibility can reveal spin entanglement between
individual constituents of a solid, while magnetisation describes their local
properties. We then show that these two thermodynamical quantities satisfy
complementary relation in the quantum-mechanical sense. It describes sharing of
(quantum) information in the solid between spin entanglement and local
properties of its individual constituents. Magnetic susceptibility is shown to
be a macroscopic spin entanglement witness that can be applied without complete
knowledge of the specific model (Hamiltonian) of the solid.Comment: 6 Pages, 2 figures, revtex
Equation of state for Entanglement in a Fermi gas
Entanglement distance is the maximal separation between two entangled
electrons in a degenerate electron gas. Beyond that distance, all entanglement
disappears. We relate entanglement distance to degeneracy pressure both for
extreme relativistic and non-relativistic systems, and estimate the
entanglement distance in a white dwarf. Treating entanglement as a
thermodynamical quantity, we relate the entropy of formation and concurrence to
relative electron distance, pressure, and temperature, to form a new equation
of state for entanglement.Comment: To appear in Phys. Rev. A., 4 pages, 1 figur
A scheme for entanglement extraction from a solid
Some thermodynamical properties of solids, such as heat capacity and magnetic
susceptibility, have recently been shown to be linked to the amount of
entanglement in a solid. However this entanglement may appear a mere
mathematical artifact of the typical symmetrization procedure of many-body wave
function in solid state physics.
Here we show that this entanglement is physical demonstrating the principles
of its extraction from a typical solid state system by scattering two particles
off the system. Moreover we show how to simulate this process using present-day
optical lattices technology. This demonstrates not only that entanglement
exists in solids but also that it can be used for quantum information
processing or for test of Bell's inequalities.Comment: 10 pages, 3 figures, published versio
Macroscopic Observables Detecting Genuine Multipartite Entanglement and Partial Inseparability in Many-Body Systems
We show a general approach for detecting genuine multipartite entanglement
(GME) and partial inseparability in many-body-systems by means of macroscopic
observables (such as the energy) only. We show that the obtained criteria, the
"GME gap" and "the k-entanglement gap", detect large areas of genuine
multipartite entanglement and partial entanglement in typical many body states,
which are not detected by other criteria. As genuine multipartite entanglement
is a necessary property for several quantum information theoretic applications
such as e.g. secret sharing or certain kinds of quantum computation, our
methods can be used to select or design appropriate condensed matter systems.Comment: 4 pages, 3 figures, published version, title extende
Entanglement as a quantum order parameter
We show that the quantum order parameters (QOP) associated with the
transitions between a normal conductor and a superconductor in the BCS and
eta-pairing models and between a Mott-insulator and a superfluid in the
Bose-Hubbard model are directly related to the amount of entanglement existent
in the ground state of each system. This gives a physical meaningful
interpretation to these QOP, which shows the intrinsically quantum nature of
the phase transitions considered.Comment: 5 pages. No figures. Revised version. References adde
Entanglement in spin-one Heisenberg chains
By using the concept of negativity, we study entanglement in spin-one
Heisenberg chains. Both the bilinear chain and the bilinear-biquadratic chain
are considered. Due to the SU(2) symmetry, the negativity can be determined by
two correlators, which greatly facilitate the study of entanglement properties.
Analytical results of negativity are obtained in the bilinear model up to four
spins and the two-spin bilinear-biquadratic model, and numerical results of
negativity are presented. We determine the threshold temperature before which
the thermal state is doomed to be entangled.Comment: 7 pages and 4 figure
Survival of entanglement in thermal states
We present a general sufficiency condition for the presence of multipartite
entanglement in thermal states stemming from the ground state entanglement. The
condition is written in terms of the ground state entanglement and the
partition function and it gives transition temperatures below which
entanglement is guaranteed to survive. It is flexible and can be easily adapted
to consider entanglement for different splittings, as well as be weakened to
allow easier calculations by approximations. Examples where the condition is
calculated are given. These examples allow us to characterize a minimum gapping
behavior for the survival of entanglement in the thermodynamic limit. Further,
the same technique can be used to find noise thresholds in the generation of
useful resource states for one-way quantum computing.Comment: 6 pages, 2 figures. Changes made in line with publication
recommendations. Motivation and concequences of result clarified, with the
addition of one more example, which applies the result to give noise
thresholds for measurement based quantum computing. New author added with new
result
Quantum correlations in the temporal CHSH scenario
We consider a temporal version of the CHSH scenario using projective
measurements on a single quantum system. It is known that quantum correlations
in this scenario are fundamentally more general than correlations obtainable
with the assumptions of macroscopic realism and non-invasive measurements. In
this work, we also educe some fundamental limitations of these quantum
correlations. One result is that a set of correlators can appear in the
temporal CHSH scenario if and only if it can appear in the usual spatial CHSH
scenario. In particular, we derive the validity of the Tsirelson bound and the
impossibility of PR-box behavior. The strength of possible signaling also turns
out to be surprisingly limited, giving a maximal communication capacity of
approximately 0.32 bits. We also find a temporal version of Hardy's nonlocality
paradox with a maximal quantum value of 1/4.Comment: corrected versio
Hybrid cluster state proposal for a quantum game
We propose an experimental implementation of a quantum game algorithm in a
hybrid scheme combining the quantum circuit approach and the cluster state
model. An economical cluster configuration is suggested to embody a quantum
version of the Prisoners' Dilemma. Our proposal is shown to be within the
experimental state-of-art and can be realized with existing technology. The
effects of relevant experimental imperfections are also carefully examined.Comment: 4 pages, 3 figures, RevTeX