480 research outputs found
Bound entanglement in the Jaynes-Cummings model
We study in detail entanglement properties of the Jaynes-Cummings model
assuming a two-level atom (qubit) interacting with the first levels of an
electromagnetic field mode (qudit) in a cavity. In the Jaynes-Cummings model,
the number operator is the conserved quantity that allows for the exact
diagonalization of the Hamiltonian and thus we study states that commute with
this conserved quantity and whose structure is preserved under the
Jaynes-Cummings dynamics. Contrary to the common belief, we show that there are
bound entangled states that satisfy the symmetries imposed by the conservation
of the number of excitations when . Furthermore we show that \emph{the
Jaynes-Cummings interaction can be used to generate bound-entanglement} between
the atom and the mode.Comment: Improved abstract, references and new section on the generation of
bound entanglement using the JC interactio
Detection of entanglement in ultracold lattice gases
We propose the use of quantum polarization spectroscopy for detecting
multi-particle entanglement of ultracold atoms in optical lattices. This
method, based on a light-matter interface employing the quantum Farady effect,
allows for the non destructive measurement of spin-spin correlations. We apply
it to the specific example of a one dimensional spin chain and reconstruct its
phase diagram using the light signal, readily measurable in experiments with
ultracold atoms. Interestingly, the same technique can be extended to detect
quantum many-body entanglement in such systems.Comment: Submitted to the Special Issue: "Strong correlations in Quantum
Gases" in The Journal of Low Temperature Physic
Genuine quantum correlations in quantum many-body systems: a review of recent progress
Quantum information theory has considerably helped in the understanding of
quantum many-body systems. The role of quantum correlations and in particular,
bipartite entanglement, has become crucial to characterise, classify and
simulate quantum many body systems. Furthermore, the scaling of entanglement
has inspired modifications to numerical techniques for the simulation of
many-body systems leading to the, now established, area of tensor networks.
However, the notions and methods brought by quantum information do not end with
bipartite entanglement. There are other forms of correlations embedded in the
ground, excited and thermal states of quantum many-body systems that also need
to be explored and might be utilised as potential resources for quantum
technologies. The aim of this work is to review the most recent developments
regarding correlations in quantum many-body systems focussing on multipartite
entanglement, quantum nonlocality, quantum discord, mutual information but also
other non classical measures of correlations based on quantum coherence.
Moreover, we also discuss applications of quantum metrology in quantum
many-body systems.Comment: Review. Close to published version. Comments are welcome! Please
write an email to g.dechiara[(at)]qub.ac.u
Probing magnetic order in ultracold lattice gases
A forthcoming challenge in ultracold lattice gases is the simulation of
quantum magnetism. That involves both the preparation of the lattice atomic gas
in the desired spin state and the probing of the state. Here we demonstrate how
a probing scheme based on atom-light interfaces gives access to the order
parameters of nontrivial quantum magnetic phases, allowing us to characterize
univocally strongly correlated magnetic systems produced in ultracold gases.
This method, which is also nondemolishing, yields spatially resolved spin
correlations and can be applied to bosons or fermions. As a proof of principle,
we apply this method to detect the complete phase diagram displayed by a chain
of (rotationally invariant) spin-1 bosons.Comment: published versio
Entanglement scaling at first order phase transitions
First order quantum phase transitions (1QPTs) are signaled, in the
thermodynamic limit, by discontinuous changes in the ground state properties.
These discontinuities affect expectation values of observables, including
spatial correlations. When a 1QPT is crossed in the vicinity of a second order
one (2QPT), due to the correlation length divergence of the latter, the
corresponding ground state is modified and it becomes increasingly difficult to
determine the order of the transition when the size of the system is finite.
Here we show that, in such situations, it is possible to apply finite size
scaling to entanglement measures, as it has recently been done for the order
parameters and the energy gap, in order to recover the correct thermodynamic
limit. Such a finite size scaling can unambigously discriminate between first
and second order phase transitions in the vicinity of multricritical points
even when the singularities displayed by entanglement measures lead to
controversial results
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