1,248 research outputs found
Experimental Quantum Cloning of Single Photons
Although perfect copying of unknown quantum systems is forbidden by the laws
of quantum mechanics, approximate cloning is possible. A natural way of
realizing quantum cloning of photons is by stimulated emission. In this context
the fundamental quantum limit to the quality of the clones is imposed by the
unavoidable presence of spontaneous emission. In our experiment a single input
photon stimulates the emission of additional photons from a source based on
parametric down-conversion. This leads to the production of quantum clones with
near optimal fidelity. We also demonstrate universality of the copying
procedure by showing that the same fidelity is achieved for arbitrary input
states.Comment: 4 pages, 2 figure
Pathway choice in DNA double strand break repair:Observations of a balancing act
Proper repair of DNA double strand breaks (DSBs) is vital for the preservation of genomic integrity. There are two main pathways that repair DSBs, Homologous recombination (HR) and Non-homologous end-joining (NHEJ). HR is restricted to the S and G2 phases of the cell cycle due to the requirement for the sister chromatid as a template, while NHEJ is active throughout the cell cycle and does not rely on a template. The balance between both pathways is essential for genome stability and numerous assays have been developed to measure the efficiency of the two pathways. Several proteins are known to affect the balance between HR and NHEJ and the complexity of the break also plays a role. In this review we describe several repair assays to determine the efficiencies of both pathways. We discuss how disturbance of the balance between HR and NHEJ can lead to disease, but also how it can be exploited for cancer treatment.</p
High-Fidelity Teleportation of Independent Qubits
Quantum teleportation is one of the essential primitives of quantum
communication. We suggest that any quantum teleportation scheme can be
characterized by its efficiency, i.e. how often it succeeds to teleport, its
fidelity, i.e. how well the input state is reproduced at the output, and by its
insensitivity to cross talk, i.e. how well it rejects an input state that is
not intended to teleport. We discuss these criteria for the two teleportation
experiments of independent qubits which have been performed thus far. In the
first experiment (Nature {\bf 390},575 (1997)) where the qubit states were
various different polarization states of photons, the fidelity of teleportation
was as high as 0.80 0.05 thus clearly surpassing the limit of 2/3 which
can, in principle, be obtained by a direct measurement on the qubit and
classical communication. This high fidelity is confirmed in our second
experiment (Phys. Rev. Lett. {\bf 80}, 3891 (1998)), demonstrating entanglement
swapping, that is, realizing the teleportation of a qubit which itself is still
entangled to another one. This experiment is the only one up to date that
demonstrates the teleportation of a genuine unknown quantum state.Comment: 13 pages, Latex, 5 figures(eps), to appear in Journal of Modern
Optic
Experimental Violation of a Spin-1 Bell Inequality Using Maximally Entangled Four-Photon States
We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.55 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27±0.02 using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations
Stimulated Emission of Polarization-Entangled Photons
Entangled photon pairs—discrete light quanta that exhibit non-classical correlations—play a crucial role in quantum information science (for example, in demonstrations of quantum non-locality1,2,3,4,5,6,7, quantum teleportation8,9 and quantum cryptography10,11,12,31). At the macroscopic optical-field level non-classical correlations can also be important, as in the case of squeezed light13, entangled light beams14,15 and teleportation of continuous quantum variables16. Here we use stimulated parametric down-conversion to study entangled states of light that bridge the gap between discrete and macroscopic optical quantum correlations. We demonstrate experimentally the onset of laser-like action for entangled photons, through the creation and amplification of the spin-1/2 and spin-1 singlet states consisting of two and four photons, respectively. This entanglement structure holds great promise in quantum information science where there is a strong demand for entangled states of increasing complexity
Experimental Quantum Cloning of Single Photons
Although perfect copying of unknown quantum systems is forbidden by the laws of quantum mechanics, approximate cloning is possible. A natural way of realizing quantum cloning of photons is by stimulated emission. In this context, the fundamental quantum limit to the quality of the clones is imposed by the unavoidable presence of spontaneous emission. In our experiment, a single input photon stimulates the emission of additional photons from a source on the basis of parametric down-conversion. This leads to the production of quantum clones with near-optimal fidelity. We also demonstrate universality of the copying procedure by showing that the same fidelity is achieved for arbitrary input states
Towards quantum superpositions of a mirror
We propose a scheme for creating quantum superposition states involving of
order atoms via the interaction of a single photon with a tiny
mirror. This mirror, mounted on a high-quality mechanical oscillator, is part
of a high-finesse optical cavity which forms one arm of a Michelson
interferometer. By observing the interference of the photon only, one can study
the creation and decoherence of superpositions involving the mirror. All
experimental requirements appear to be within reach of current technology.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let
The diagonal and off-diagonal quark number susceptibility of high temperature and finite density QCD
We study the quark number susceptibility of the hot quark-gluon plasma at
zero and non-zero quark number density, using lattice Monte Carlo simulations
of an effective theory of QCD, electrostatic QCD (EQCD). Analytic continuation
is used to obtain results at non-zero quark chemical potential. We measure both
flavor singlet (diagonal) and non-singlet (off-diagonal) quark number
susceptibilities. The diagonal susceptibility approaches the perturbative
result above 20T_c, but below that temperature we observe significant
deviations. The results agree well with 4d lattice data down to temperatures
2T_c. The off-diagonal susceptibility is more prone to statistical and
systematic errors, but the results are consistent with perturbation theory
already at 10T_c.Comment: 21 pages, 8 figures. Published version, references added, conclusions
unchange
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