A. S. Coelho
University of São Paulo
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Featured researches published by A. S. Coelho.
Science | 2009
A. S. Coelho; F. A. S. Barbosa; K. N. Cassemiro; Alessandro S. Villar; Marcelo Martinelli; P. Nussenzveig
Entangling Rainbows Quantum mechanical entanglement is at the heart of quantum information processing. In the future, practical systems will contain a network of quantum components, possibly operating at different frequencies. Coelho et al. (p. 823, published online 17 September) present a technique that can entangle light beams of three different frequencies. The ability to swap entanglement between different light fields should prove useful in advanced quantum information protocols on systems comprising different operating frequencies. Three bright light beams of different colors can be entangled. Entanglement is an essential quantum resource for the acceleration of information processing as well as for sophisticated quantum communication protocols. Quantum information networks are expected to convey information from one place to another by using entangled light beams. We demonstrated the generation of entanglement among three bright beams of light, all of different wavelengths (532.251, 1062.102, and 1066.915 nanometers). We also observed disentanglement for finite channel losses, the continuous variable counterpart to entanglement sudden death.
Physical Review A | 2012
M. Bellini; A. S. Coelho; S. Filippov; Alessandro Zavatta; E. Fermi; P. N. Lebedev
We present the results of an operational use of experimentally measured optical tomograms to determine state characteristics (purity) avoiding any reconstruction of quasiprobabilities. We also develop a natural way how to estimate the errors (including both statistical and systematic ones) by an analysis of the experimental data themselves. Precision of the experiment can be increased by postselecting the data with minimal (systematic) errors. We demonstrate those techniques by considering coherent and photon-added coherent states measured via the time-domain improved homodyne detection. The operational use and precision of the data allowed us to
Nature Photonics | 2010
F. A. S. Barbosa; A. S. Coelho; A. J. de Faria; K. N. Cassemiro; Alessandro S. Villar; P. Nussenzveig; Marcelo Martinelli
Quantum entanglement — used for quantum key distribution, communication and teleportation — is a fragile resource. Researchers investigate the conditions under which optical loss destroys entanglement, and report states that are particularly robust to such losses.
Physical Review Letters | 2013
F. A. S. Barbosa; A. S. Coelho; K. N. Cassemiro; P. Nussenzveig; Claude Fabre; Marcelo Martinelli; Alessandro S. Villar
Spectral homodyne detection, a widely used technique for measuring quantum properties of light beams, cannot retrieve all the information needed to reconstruct the quantum state of spectral field modes. We show that full quantum state reconstruction can be achieved with the alternative measurement technique of resonator detection. We experimentally demonstrate this difference by engineering a quantum state with features that go undetected by homodyne detection but are clearly revealed by resonator detection.
Physical Review A | 2011
F. A. S. Barbosa; A. J. de Faria; A. S. Coelho; K. N. Cassemiro; Alessandro S. Villar; P. Nussenzveig; Marcelo Martinelli
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 situation 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 | 2013
F. A. S. Barbosa; A. S. Coelho; K. N. Cassemiro; P. Nussenzveig; Claude Fabre; Alessandro S. Villar; Marcelo Martinelli
We revisit the problem of quantum state reconstruction of light beams from the photocurrent quantum noise. As is well-known, but often overlooked, two longitudinal field modes contribute to each spectral component of the photocurrent (sideband modes). We show that spectral homodyne detection is intrinsically incapable of providing all the information needed for the full reconstruction of the two-mode spectral quantum state. Such a limitation is overcome by the technique of resonator detection. A detailed theoretical description and comparison of both methods is presented, as well as an experiment to measure the six-mode quantum state of pump-signal-idler beams of an optical parametric oscillator above the oscillation threshold.
european quantum electronics conference | 2009
A. S. Coelho; J. E. S. Cesar; K. N. Cassemiro; Alessandro S. Villar; P. Nussenzveig; Marcelo Martinelli
Recent experiments with Optical Parametric Oscillators have shown [1–3] that an unpredicted extra noise on the phase of the fields reduces the level of squeezing or quantum correlations. In some cases, it can hinder the attempts to observe entanglement in those systems [4]. It is probably the main reason why signal and idler entanglement above threshold remained unobserved by almost 20 years after its prediction [5].
Physica Scripta | 2013
S. Filippov; V. I. Man'ko; A. S. Coelho; Alessandro Zavatta; M. Bellini
Travelling modes of single-photon-added coherent states (SPACS) are characterized via optical homodyne tomography. Given a set of experimentally measured quadrature distributions, we estimate parameters of the state and also extract information about the detector efficiency. The method used is a minimal distance estimation between theoretical and experimental quantities, which additionally allows to evaluate the precision of estimated parameters. Given experimental data, we also estimate the lower and upper bounds on fidelity. The results are believed to encourage preciser engineering and detection of SPACS.
Physical Review Letters | 2016
A. S. Coelho; Luca S. Costanzo; Alessandro Zavatta; Catherine Hughes; M. S. Kim; Marco Bellini
We experimentally demonstrate a universal strategy for producing a quantum state that is orthogonal to an arbitrary, infinite-dimensional, pure input one, even if only a limited amount of information about the latter is available. Arbitrary coherent superpositions of the two mutually orthogonal states are then produced by a simple change in the experimental parameters. We use input coherent states of light to illustrate two variations of the method. However, we show that the scheme works equally well for arbitrary input fields and constitutes a universal procedure, which may thus prove a useful building block for quantum state engineering and quantum information processing with continuous-variable qubits.
Physical Review Letters | 2016
L. S. Costanzo; A. S. Coelho; D. Pellegrino; Milrian S. Mendes; L. H. Acioli; K. N. Cassemiro; D. Felinto; Alessandro Zavatta; M. Bellini
Broadband single photons are usually considered not to couple efficiently to atomic gases because of the large mismatch in bandwidth. Contrary to this intuitive picture, here we demonstrate that the interaction of ultrashort single photons with a dense resonant atomic sample deeply modifies the temporal shape of their wave packet mode without degrading their nonclassical character, and effectively generates zero-area single-photon pulses. This is a clear signature of strong transient coupling between single broadband (THz-level) light quanta and atoms, with intriguing fundamental implications and possible new applications to the storage of quantum information.