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Search Results: 1 - 10 of 325281 matches for " S. Castelletto "
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A Modified Wigner's Inequality for Secure Quantum Key Distribution
S. Castelletto,I. P. Degiovanni,M. L. Rastello
Physics , 2003, DOI: 10.1103/PhysRevA.67.044303
Abstract: In this report we discuss the insecurity with present implementations of the Ekert protocol for quantum-key distribution based on the Wigner Inequality. We propose a modified version of this inequality which guarantees safe quantum-key distribution.
Single Photon Source with Individualized Single Photon Certifications
A. L. Migdall,D. Branning,S. Castelletto,M. Ware
Physics , 2002, DOI: 10.1117/12.452038
Abstract: As currently implemented, single-photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand. The scheme uses a heralded photon source based on parametric downconversion, but by effectively breaking the trigger detector area into multiple regions, we are able to extract more information about a heralded photon than is possible with a conventional arrangement. This scheme allows photons to be produced along with a quantitative ``certification'' that they are single photons. Some of the single-photon certifications can be significantly better than what is possible with conventional downconversion sources (using a unified trigger detector region), as well as being better than faint laser sources. With such a source of more tightly certified single photons, it should be possible to improve the maximum secure bit rate possible over a quantum cryptographic link. We present an analysis of the relative merits of this method over the conventional arrangement.
Experimental evidence for bounds on quantum correlations
F. A. Bovino,G. Castagnoli,I. P. Degiovanni,S. Castelletto
Physics , 2003, DOI: 10.1103/PhysRevLett.92.060404
Abstract: We implemented the experiment proposed by Cabello [arXiv:quant-ph/0309172] to test the bounds of quantum correlation. As expected from the theory we found that, for certain choices of local observables, Cirel'son's bound of the Clauser-Horne-Shimony-Holt inequality ($2\sqrt{2}$) is not reached by any quantum states.
Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate
S. Castelletto,I. P. Degiovanni,V. Schettini,A. Migdall
Physics , 2006, DOI: 10.1088/0026-1394/43/2/S12
Abstract: We explore the feasibility of using high conversion-efficiency periodically-poled crystals to produce photon pairs for photon-counting detector calibrations at 1550 nm. The goal is the development of an appropriate parametric down-conversion (PDC) source at telecom wavelengths meeting the requirements of high-efficiency pair production and collection in single spectral and spatial modes (single-mode fibers). We propose a protocol to optimize the photon collection, noise levels and the uncertainty evaluation. This study ties together the results of our efforts to model the single-mode heralding efficiency of a two-photon PDC source and to estimate the heralding uncertainty of such a source.
Reduced Deadtime and Higher Rate Photon-Counting Detection using a Multiplexed Detector Array
S. Castelletto,I. P. Degiovanni,V. Schettini,A. Migdall
Physics , 2006, DOI: 10.1080/09500340600779579
Abstract: We present a scheme for a photon-counting detection system that can be operated at incident photon rates higher than otherwise possible by suppressing the effects of detector deadtime. The method uses an array of N detectors and a 1-by-N optical switch with a control circuit to direct input light to live detectors. Our calculations and models highlight the advantages of the technique. In particular, using this scheme, a group of N detectors provides an improvement in operation rate that can exceed the improvement that would be obtained by a single detector with deadtime reduced by 1/N, even if it were feasible to produce a single detector with such a large improvement in deadtime. We model the system for continuous and pulsed light sources, both of which are important for quantum metrology and quantum key distribution applications.
Tailoring Single and Multiphoton Probabilities of a Single Photon On-Demand Source
A. L. Migdall,D. Branning,S. Castelletto,M. Ware
Physics , 2002, DOI: 10.1103/PhysRevA.66.053805
Abstract: As typically implemented, single photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand.
Quantum and Classical Noise in Practical Quantum Cryptography Systems based on polarization-entangled photons
S. Castelletto,I. P. Degiovanni,M. L. Rastello
Physics , 2002, DOI: 10.1103/PhysRevA.67.022305
Abstract: Quantum-cryptography key distribution (QCKD) experiments have been recently reported using polarization-entangled photons. However, in any practical realization, quantum systems suffer from either unwanted or induced interactions with the environment and the quantum measurement system, showing up as quantum and, ultimately, statistical noise. In this paper, we investigate how ideal polarization entanglement in spontaneous parametric downconversion (SPDC) suffers quantum noise in its practical implementation as a secure quantum system, yielding errors in the transmitted bit sequence. Because all SPDC-based QCKD schemes rely on the measurement of coincidence to assert the bit transmission between the two parties, we bundle up the overall quantum and statistical noise in an exhaustive model to calculate the accidental coincidences. This model predicts the quantum-bit error rate and the sifted key and allows comparisons between different security criteria of the hitherto proposed QCKD protocols, resulting in an objective assessment of performances and advantages of different systems.
Imaging and quantum efficiency measurement of chromium emitters in diamond
I. Aharonovich,S. Castelletto,B. C. Gibson,B. C. Johnson,S. Prawer
Physics , 2010,
Abstract: We present direct imaging of the emission pattern of individual chromium-based single photon emitters in diamond and measure their quantum efficiency. By imaging the excited state transition dipole intensity distribution in the back focal plane of high numerical aperture objective, we determined that the emission dipole is oriented nearly orthogonal to the diamond-air interface. Employing ion implantation techniques, the emitters were engineered with various proximities from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, an average quantum efficiency of 28% was measured.
Engineering chromium related single photon emitters in single crystal diamond
I Aharonovich,S Castelletto,B C Johnson,J C McCallum,S Prawer
Physics , 2010, DOI: 10.1088/1367-2630/13/4/045015
Abstract: Color centers in diamond as single photon emitters, are leading candidates for future quantum devices due to their room temperature operation and photostability. The recently discovered chromium related centers are particularly attractive since they possess narrow bandwidth emission and a very short lifetime. In this paper we investigate the fabrication methodologies to engineer these centers in monolithic diamond. We show that the emitters can be successfully fabricated by ion implantation of chromium in conjunction with oxygen or sulfur. Furthermore, our results indicate that the background nitrogen concentration is an important parameter, which governs the probability of success to generate these centers.
Photophysics of novel diamond based single photon emitters
I. Aharonovich,S. Castelletto,D. A. Simpson,A. D. Greentree,S. Prawer
Physics , 2009, DOI: 10.1103/PhysRevA.81.043813
Abstract: A detailed study of the photophysical properties of several novel color centers in chemical vapor deposition diamond is presented. These emitters show narrow luminescence lines in the near infra-red. Single photon emission was verified with continuous and pulsed excitation with emission rates at saturation in the MHz regime, whilst direct lifetime measurements reveal excited state lifetimes ranging from 1-14 ns. In addition, a number of quantum emitters demonstrate two level behavior with no bunching present in the second order correlation function. An improved method of evaluating the quantum efficiency through the direct measurement of the collection efficiency from two level emitters is presented and discussed. \
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