A. J. de Faria

University of São Paulo, San Paulo, São Paulo, Brazil

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Publications (4)30.3 Total impact

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    ABSTRACT: Entanglement as a collective property of quantum systems follows its own dynamics as environmental disturbances enter the quantum channel. It can either withstand undesired external influences or completely vanish even for very small disturbances. Only the first kind of quantum states are suitable for real applications in quantum networks. We show the conditions under which a bipartite Gaussian state remains entangled under partial energy loss of one party.
    10/2011;
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    ABSTRACT: Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.
    Physical Review A 09/2010; · 3.04 Impact Factor
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    ABSTRACT: Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications. Comment: To be published - Nature Photonics
    Nature Photonics 09/2010; · 27.25 Impact Factor
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    ABSTRACT: Entanglement may vanish even for a limited amount of loss imposed on the quantum state, a phenomenon known as entanglement sudden death in discrete systems, or, as proposed, early stage disentanglement (ESD) in continuous variables. The resilience to ESD, or {\it entanglement robustness}, is an essential property of entangled systems intended to convey quantum information through realistic quantum channels. We investigate the robustness of bipartite entanglement in continuous-variables systems, which we classify according to their robustness in different loss scenarios. The sufficient conditions specifying each robustness class are determined. These conditions turn out to be necessary and sufficient for Gaussian states. We find that in general states subject to ESD lie close to the border between entangled and separable states.
    01/2010;