85 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
Nou mètode per detectar estats "exòtics" de la matèria condensada
El grup de computació quàntica de la UAB ha participat en una recerca internacional que proposa un mètode nou, superior als que existeixen fins ara, per detectar estats "exòtics" de la matèria condensada, de tal manera que la mostra (àtoms ultrafreds) no es destrueixi en ser observada. Aquest mètode s'ha anomenat Quantum non demolition, i és la mesura menys destructiva possible que permeten les lleis de la mecànica quàntica. Aquest treball, publicat a Nature, s'ha dut a terme en col·laboració amb l'Institut de Ciències Fotòniques (ICFO) i el Niels Bohr Institute de Dinamarca.El grupo de computación cuántica de la UAB ha liderado una investigación que propone un método nuevo, superior a los que existen hasta ahora, para detectar estados "exóticos" de la materia condensada de tal manera que la muestra (átomos ultrafríos) no se destruya al ser observada. Este método se ha llamado Quantum non demolition, y es la medida menos destructiva posible que permiten las leyes de la mecánica cuántica. Este trabajo, publicado en Nature, se ha llevado a cabo en colaboración con el Instituto de Ciencias Fotónicas (ICFO) y el Niels Bohr Institute de Dinamarca
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