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| Author |
Shor, Peter W. |
| Title |
Quantum information theory: The bits don't add up |
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Journal Article |
| Year |
2009 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
| Volume |
5 |
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247 - 248 |
| Keywords |
fromIPMRAS |
| Abstract |
A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel. |
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RPLAB @ gujma @ |
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800 |
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| Author |
Trabesinger, Andreas |
| Title |
Quantum mechanics: Shaken foundations |
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Journal Article |
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2009 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
| Volume |
5 |
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12 |
Pages |
863 |
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fromIPMRAS |
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802 |
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| Author |
Benford, Dominic; Moseley, Harvey; Zmuidzinas, Jonas |
| Title |
Direct detectors for the Einstein inflation probe |
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Conference Article |
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2009 |
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J. Phys.: Conf. Ser. |
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J. Phys.: Conf. Ser. |
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155 |
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1 |
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012001 (1 to 49) |
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KID, MKID, CMB |
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Here we review the principles of operation, history, present status, and future prospects for the primary candidate detectors for Cosmic Microwave Background (CMB) polarization studies. The three detector types we will discuss are semiconductor-based bolometers, superconducting transition edge sensor (TES) bolometer, and Microwave Kinetic Inductance Detectors (MKIDs). All of these detector types can provide the sensitivity to permit background-limited measurements of the CMB, but the ultimate selection of detectors will be largely determined by the ease of production and reliability of large arrays of such detectors. This paper describes the present state of development of these detectors, efforts to integrate them into large arrays, and the detector system developments necessary to enable a space CMB polarization mission. |
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Recommended by Klapwijk |
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913 |
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Pekker, David; Shah, Nayana; Sahu, Mitrabhanu; Bezryadin, Alexey; Goldbart, Paul M. |
| Title |
Stochastic dynamics of phase-slip trains and superconductive-resistive switching in current-biased nanowires |
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Journal Article |
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2009 |
Publication |
Phys. Rev. B |
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80 |
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214525 (1 to 17) |
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superconducting nanowire, phase-slip, order parameter, HEB distributed model, HEB model |
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Superconducting nanowires fabricated via carbon-nanotube templating can be used to realize and study quasi-one-dimensional superconductors. However, measurement of the linear resistance of these nanowires have been inconclusive in determining the low-temperature behavior of phase-slip fluctuations, both quantal and thermal. Thus, we are motivated to study the nonlinear current-voltage characteristics in current-biased nanowires and the stochastic dynamics of superconductive-resistive switching, as a way of probing phase-slip events. In particular, we address the question: can a single phase-slip event occurring somewhere along the wire—during which the order-parameter fluctuates to zero—induce switching, via the local heating it causes? We explore this and related issues by constructing a stochastic model for the time evolution of the temperature in a nanowire whose ends are maintained at a fixed temperature. We derive the corresponding master equation as a tool for evaluating and analyzing the mean switching time at a given value of current (smaller than the depairing critical current). The model indicates that although, in general, several phase-slip events are necessary to induce switching via a thermal runaway, there is indeed a regime of temperatures and currents in which a single event is sufficient. We carry out a detailed comparison of the results of the model with experimental measurements of the distribution of switching currents, and provide an explanation for the rather counterintuitive broadening of the distribution width that is observed upon lowering the temperature. Moreover, we identify a regime in which the experiments are probing individual phase-slip events, and thus offer a way of unearthing and exploring the physics of nanoscale quantum tunneling of the one-dimensional collective quantum field associated with the superconducting order parameter. |
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923 |
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Sahu, Mitrabhanu; Bae, Myung-Ho; Rogachev, Andrey; Pekker, David; Wei, Tzu-Chieh; Shah, Nayana; Goldbart, Paul M.; Bezryadin, Alexey |
| Title |
Individual topological tunnelling events of a quantum field probed through their macroscopic consequences |
Type |
Journal Article |
| Year |
2009 |
Publication |
Nature Phys. |
Abbreviated Journal |
Nature Phys. |
| Volume |
5 |
Issue |
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Pages |
503-508 |
| Keywords |
phase slips, superconducting nanowires |
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Phase slips are topological fluctuations that carry the superconducting order-parameter field between distinct current-carrying states. Owing to these phase slips, superconducting nanowires acquire electrical resistance. In such wires, it is well known that at higher temperatures phase slips occur through the process of thermal barrier-crossing by the order-parameter field. At low temperatures, the general expectation is that phase slips should proceed through quantum tunnelling events, which are known as quantum phase slips. However, resistive measurements have produced evidence both for and against the occurrence of quantum phase slips. Here, we report evidence for the observation of individual quantum phase-slip events in homogeneous ultranarrow wires at high bias currents. We accomplish this through measurements of the distribution of switching currents for which the width exhibits a rather counter-intuitive, monotonic increase with decreasing temperature. Importantly, measurements show that in nanowires with larger critical currents, quantum fluctuations dominate thermal fluctuations up to higher temperatures. |
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