Raphael C. Drumond

Asymptotic entanglement dynamics and geometry of quantum states

A given dynamics for a composite quantum system can exhibit several distinct properties for the asymptotic entanglement behavior, such as entanglement sudden death, asymptotic death of entanglement, sudden birth of entanglement, etc. A classification of the possible situations was given by Terra Cunha (2007 New J. Phys. 9 237) but for some classes there were no known examples. In this work, we give a better classification for the possible relaxing dynamics in light of the geometry of their set of asymptotic states and give explicit examples for all the classes. Although the classification is completely general, in the search for examples it is sufficient to use two qubits with dynamics given by differential equations in the Lindblad form (some of them are non-autonomous). We also investigate, in each case, the probabilities of finding each possible behavior for random initial states.

Quantum dynamics of bosons in a double-well potential : Josephson oscillations, self-trapping and ultralong tunneling times

Abstract.The dynamics of the population imbalance of bosons in a double-well potential is investigated from the point of view of many-body quantum mechanics in the framework of the two-mode model. For small initial population imbalances, coherent superpositions of almost equally spaced energy eigenstates lead to Josephson oscillations. The suppression of tunneling at population imbalances beyond a critical value is related to a high concentration of initial state population in the region of the energy spectrum with quasi-degenerate doublets. Negligible coherences among adjacent doublets result in imbalance oscillations with a very small amplitude. For unaccessible long times, however, the system recovers the regime of Josephson oscillations.

Double-slit implementation of the minimal Deutsch algorithm

We report an experimental implementation of the minimal Deutsch algorithm in an optical setting. In this version, a redundancy is removed from the most famous form of the algorithm. The original version involves manipulation of two qubits, while in its minimal version, only one qubit is used. Our qubit is encoded in the transversal spatial modes of a spontaneous parametric down-converted signal photon, with the aid of a double slit, with the idler photon playing a crucial role in creating a heralded single photon source. A spatial light modulator (SLM) is programmed to physically generate one-bit functions necessary to implement the algorithms minimal version, which shows that the SLM can be used in future implementations of quantum protocols.

Mixedness and entanglement for two-mode Gaussian states

Abstract We analytically exploit the two-mode Gaussian states nonunitary dynamics. We show that in the zero temperature limit, entanglement sudden death (ESD) will always occur for symmetric states (where initial single-mode compression is z0) provided that the two mode squeezing r0 satisfies 0 r 0 1 2 log ( cosh ( 2 z 0 ) ) . We also give the analytical expressions for the time of ESD. Finally, we show the relation between the single modes initial impurities and the initial entanglement, where we exhibit that the latter is suppressed by the former.

Small violations of full-correlation Bell inequalities for multipartite pure random states

We estimate the probability of random

Small violations of Bell inequalities for multipartite pure random states

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Universality of finite time disentanglement

-qudit pure states violating full-correlation Bell inequalities with two dichotomic observables per site. These inequalities can show violations that grow exponentially with

Nonequilibrium localization and the interplay between disorder and interactions

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Self-catalytic conversion of pure quantum states

, but we prove this is not the typical case. For many-qubit states the probability to violate any of these inequalities by an amount that grows linearly with

Geometry of Entanglement Sudden Death: Explicit Examples

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