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Summary form only given. One of the key elements of quantum communication is the generation of maximally entangled states between distant nodes of a quantum network. We present an entanglement purification scheme which generates maximally entangled states in finite Hilbert spaces from the continuous two-mode squeezed states. With high probabilities, we get a more entangled stale, and the entanglement...
Summary form only given. Correlated and entangled single photon states have made possible many fundamental studies in quantum optics such as the Bell-type test of hidden variables and non-locality, explorations of quantum interference properties, and investigations of quantum information processing and quantum communications technologies such as quantum cryptography, quantum computing, and quantum...
Summary form only given. We have experimentally demonstrated that the two-photon probability amplitudes of photon pairs generated using spontaneous parametric down conversion from separate nonlinear crystals, under the conditions outlined above, remain independent and cannot be used to engineer more complex quantum states. The spontaneous nature of the down-conversion process prevents pairs of photons...
Summary form only given. A type-II phase-marched parametric downconverter can be used to produce polarization-entangled photon pairs. We propose a production scheme for polarization-entangled photon pairs by using a pair of optical parametric amplifiers (OPAs) whose narrowband generation rate is high enough to make it a practical source for a trapped-atom quantum memory. For a type-II system using...
Summary form only given. We report the observation of an interesting coherent effect, which looks very much like the so-called Zeeman coherence in atomic physics and is indeed an optically induced entanglement between two oppositely oriented electrons confined to one single QD. This is the first observation of entanglement in semiconductors and is an important step in realizing a quantum logic device...
Summary form only given. Exciting observations of ultra-slow group velocities and very large nonlinearities in coherently driven atomic media open up interesting prospectives for nonlinear optical processes at low light levels. Recent experiments, for instance, demonstrated that very efficient nonlinear phenomena can be induced by laser fields of tiny energies. These developments stimulate the studies...
Summary form only given. Entangled states of multi-particle systems are arguably the quintessential feature of quantum mechanics. In addition to their central role in discussions of non-local quantum correlations, they form the basis of quantum information, and enable such phenomena as quantum cryptography, quantum dense coding, teleportation, and quantum computation. Via the process of spontaneous...
Summary form only given. The notion of entanglement was coined by Erwin Schrodinger in order to signify the peculiar properties of quantum correlations. Entanglement is at the heart of the Einstein-Podolsky-Rosen paradox and Bell's theorem. While, originally, entanglement was considered to be a very important fundamental concept in quantum mechanics leading to such concepts as quantum nonlocality,...
Summary form only given. We perform experiments in which atoms interact one at a time with a few photons in a cavity. Entanglement between atoms and photons is produced under well controlled conditions, leading to textbook demonstrations of basic quantum concepts. Among recent experiments performed at ENS, we will focus on an ideal nondestructive detection of a single photon which amounts to the operation...
Summary form only given. Ground state cooling and coherent manipulation of ions in a rf-(Paul) trap is the prerequisite for quantum information experiments with trapped ions. In our experiments a single /sup 40/Ca/sup +/ ion in a conventional Paul trap has been cooled to the ground state of vibration with 99.9% (98%) probability in the axial (radial) trap direction. We use a continuous resolved sideband...
Summary form only given. Quantum entanglement is a fundamental element of schemes for quantum communication, cryptography, and computation. In a previous experiment, we demonstrated that two-particle entanglement could be generated in a deterministic way using trapped ions. However, that scheme also could not easily be applied to more particles in a single trap, because it relied on the particular...
Summary form only given. We report on a scheme for the generation of bright entangled light beams aimed at quantum communication applications. The experiment is based on the recently proposed theme where two intense independently squeezed light fields interfere to produce multi-photon entangled light fields. An asymmetric fibre Sagnac interferometer is used.
Summary form only given. It has been known for some time that entangled photon pairs, such as generated by spontaneous parametric down conversion, have unusual imaging characteristics with sub-shot-noise interferometric phase measurement. In fact, Fonseca, et al., recently demonstrated resolution of a two-slit diffraction patterned at half the Rayleigh limit in a coincidence counting experiment. What...
Summary form only given. Quantum cryptography uses single photons to allow secure distribution of secret key material to sender and receiver, without the possibility of an undetected eavesdropper. In the protocol suggested by Ekert, each photon of a quantum-mechanically entangled pair is sent to the sender and receiver, who randomly measure the polarization in various bases. If the bases are the same,...
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