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 $N$ 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 $N>3$. 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