RESUMO
The establishment of nonlocal correlations, guaranteed through the violation of a Bell inequality, is not only important from a fundamental point of view but constitutes the basis for device-independent quantum information technologies. Although several nonlocality tests have been conducted so far, all of them suffered from either locality or detection loopholes. Among the proposals for overcoming these problems are the use of atom-photon entanglement and hybrid photonic measurements (for example, photodetection and homodyning). Recent studies have suggested that the use of atom-photon entanglement can lead to Bell inequality violations with moderate transmission and detection efficiencies. Here we combine these ideas and propose an experimental setup realizing a simple atom-photon entangled state that can be used to obtain nonlocality when considering realistic experimental parameters including detection efficiencies and losses due to required propagation distances.
RESUMO
We present a method to implement ultrafast two-qubit gates valid for the ultrastrong coupling and deep strong coupling regimes of light-matter interaction, considering state-of-the-art circuit quantum electrodynamics technology. Our proposal includes a suitable qubit architecture and is based on a four-step sequential displacement of the intracavity field, operating at a time proportional to the inverse of the resonator frequency. Through ab initio calculations, we show that these quantum gates can be performed at subnanosecond time scales while keeping a fidelity above 99%.
RESUMO
We investigated the preservation of information encoded into the relative phase and amplitudes of optical pulses during storage and retrieval in an optical memory based on stimulated photon echo. By interfering photon echoes produced in a single-mode Ti:Er:LiNbO(3) waveguide, we found that decoherence in the medium translates only as loss and not as degradation of information. We measured a visibility for interfering echoes close to 100%. These results may have important implications for future long-distance quantum communication protocols.
RESUMO
We consider a family of quantum communication protocols involving N partners. We demonstrate the existence of a link between the security of these protocols against individual attacks by the eavesdropper, and the violation of some Bell's inequalities, generalizing the link that was noticed some years ago for two-partners quantum cryptography. The arguments are independent of the local hidden variable debate.
RESUMO
We evaluated frequency and type of adverse events (AE) and measures adopted in outpatients attending a hospital hypertension unit in a two-part study: (1) a retrospective review of the charts of the 412 patients seen in 1991 with at least one follow-up visit and (2) a prospective study of the 491 patients seen in 1993 with at least one follow-up visit for whom physicians were asked to fill out an AE form. In 1991 18.6% of patients spontaneously reported an AE; those with an AE were older (p<0.001) than those without and included a greater proportion of females (p<0.002). This retrospective analysis of AE is reproducible as demonstrated by a blind review of 30 randomly selected charts undertaken by two independent observers (McNemar's test:p=ns). In 1993 AE were reported by 24.4% of patients who had more follow-up visits (p<0.001) and included a higher proportion of females (p=0.016) than the subgroup without AE. AE were different in the two studies (p<0.001), more specific and drug-related in 1993. AE were usually considered as mild or moderate (87.4%), the drugs most often involved were calcium antagonists and ACE-inhibitors and the measure adopted was switching to another substance (44%). The frequency of AE reporting varied widely between different physicians.