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- Murilo P. Almeida, Fernando M de Melo, +4 authors Luiz Davidovich
- Science
- 2007

We demonstrate the difference between local, single-particle dynamics and global dynamics of entangled quantum systems coupled to independent environments. Using an all-optical experimental setup, we showed that, even when the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear. This "sudden death" constitutes… (More)

- S. P. Walborn, D. S. Lemelle, Murilo P. Almeida, P. H. Souto Ribeiro
- Physical review letters
- 2006

We present a proof of principle demonstration of a quantum key distribution scheme in higher-order -dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate… (More)

- Daniel Cavalcanti, Paul Skrzypczyk, Giovanna Aguilar, Rowena Nery, P. H. Souto Ribeiro, S. P. Walborn
- Nature communications
- 2015

The future of quantum communication relies on quantum networks composed by observers sharing multipartite quantum states. The certification of multipartite entanglement will be crucial to the usefulness of these networks. In many real situations it is natural to assume that some observers are more trusted than others in the sense that they have more… (More)

- Regina M. Gomes, Alejo Salles, Fabricio Toscano, P. H. Souto Ribeiro, S. P. Walborn
- Physical review letters
- 2009

We report the observation of an optical vortex in the correlations of photons produced from spontaneous parametric down-conversion. The singularity appears in a nonlocal coordinate plane consisting of 1 degree of freedom of each photon.

- P. H. Souto Ribeiro, C. H. Monken, Geraldo A. Barbosa
- Applied optics
- 1994

The coherence area is measured in a simple Young's experiment using parametric downconversion light produced in a nonlinear crystal (LiIO(3)) pumped by a continuous argon-ion laser. The normalized mutual intensity or degree of coherence is obtained from the intensity distribution interference patterns and compared with a standard theory in which the light… (More)

- Douglas Soares Gonçalves, Márcia A. Gomes-Ruggiero, Carlile Lavor, Osvaldo Jiménez Farias, P. H. Souto Ribeiro
- Quantum Information & Computation
- 2012

Maximum likelihood estimation is one of the most used methods in quantum state tomography, where the aim is to find the best density matrix for the description of a physical system. Results of measurements on the system should match the expected values produced by the density matrix. In some cases however, if the matrix is parameterized to ensure positivity… (More)

- Giovanna Aguilar, Osvaldo Jiménez Farias, Jonas Maziero, Roberto M Serra, P. H. Souto Ribeiro, S. P. Walborn
- Physical review letters
- 2012

The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system's state and numerical optimization procedures. Thus, it is natural to seek methods involving… (More)

- E. C. Paul, M O Hor-Meyll, P. H. Souto Ribeiro, S. P. Walborn
- Scientific reports
- 2014

We demonstrate the use of a phase-only spatial light modulator for the measurement of transverse spatial distributions of coincidence counts between twin photon beams, in a fully automated fashion. This is accomplished by means of the polarization dependence of the modulator, which allows the conversion of a phase pattern into an amplitude pattern. We also… (More)

- Gabriela Barreto Lemos, P. H. Souto Ribeiro, S. P. Walborn
- Journal of the Optical Society of America. A…
- 2014

We experimentally implement an optical algorithm for integration of a real-valued bivariate function. A user-defined function is encoded in the position-dependent phase of one of the polarization components of an optical beam. The integral of this function is retrieved by measuring a Stokes parameter of the polarization. We analyze the performance of the… (More)

- Marcio Fernando Cornelio, Osvaldo Jiménez Farias, +7 authors P. H. Souto Ribeiro
- Physical review letters
- 2012

We use the classical correlation between a quantum system being measured and its measurement apparatus to analyze the amount of information being retrieved in a quantum measurement process. Accounting for decoherence of the apparatus, we show that these correlations may have a sudden transition from a decay regime to a constant level. This transition… (More)