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We estimate the depairing current of superconducting nanowire single-photon detectors (SNSPDs) by studying the dependence of the nanowires' kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator-style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured resonant frequency correspond to the change in the kinetic inductance, which can be compared with theoretical predictions. We demonstrate that the fast relaxation model described in the literature accurately matches our experimental data and provides a valuable tool for determination of the depairing current. Accurate measurement of the depairing current is critical for nanowire quality analysis, as well as modeling efforts aimed at understanding the detection mechanism in SNSPDs.

The nature of the magnetic-field driven superconductor-to-insulator quantum-phase transition in two-dimensional systems at zero temperature has been under debate since the 1980s, and became even more controversial after the observation of a quantum-Griffiths singularity. Whether it is induced by quantum fluctuations of the superconducting phase and the localization of Cooper pairs, or is directly driven by depairing of these pairs, remains an open question. We herein experimentally demonstrate that in weakly-pinning systems and in the limit of infinitely wide films, a sequential superconductor-to-Bose insulator-to-Fermi insulator quantum-phase transition takes place. By limiting their size to smaller than the effective penetration depth, however, the vortex interaction alters, and the superconducting state re-enters the Bose-insulating state. As a consequence, one observes a direct superconductor-to-Fermi insulator in the zero-temperature limit. In narrow films, the associated critical-exponent products diverge along the corresponding phase boundaries with increasing magnetic field, which is a hallmark of the quantum-Griffiths singularity.

We estimate the depairing current of superconducting nanowire single photon detectors (SNSPDs) by studying the dependence of the nanowires kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured resonant frequency correspond to the change in the kinetic inductance, which can be compared with theoretical predictions. We demonstrate that the fast relaxation model described in the literature accurately matches our experimental data and provides a valuable tool for direct determination of the depairing current. Accurate and direct measurement of the depairing current is critical for nanowire quality analysis, as well as modeling efforts aimed at understanding the detection mechanism in SNSPDs.

We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T*(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest the presence of a highly conducting region that is dominating the electric transport in narrow bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.

John Bells theorem of 1964 states that local elements of physical reality, existing independent of measurement, are inconsistent with the predictions of quantum mechanics (Bell, J. S. (1964), Physics (College. Park. Md). 1 (3), 195). Specifically, correlations between measurement results from distant entangled systems would be smaller than predicted by quantum physics. This is expressed in Bells inequalities. Employing modifications of Bells inequalities, many experiments have been performed that convincingly support the quantum predictions. Yet, all experiments rely on assumptions, which provide loopholes for a local realist explanation of the measurement. Here we report an experiment with polarization-entangled photons that simultaneously closes the most significant of these loopholes. We use a highly efficient source of entangled photons, distributed these over a distance of 58.5 meters, and implemented rapid random setting generation and high-efficiency detection to observe a violation of a Bell inequality with high statistical significance. The merely statistical probability of our results to occur under local realism is less than 3.74 . 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Research Council Project AQUMET; European Union Project QUIC [641122]; Spanish MINECO under Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project XPLICA [FIS2014-62181-EXP]; Catalan AGAUR SGR [1295, 1623]; European Regional Development Fund (FEDER) [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS Grant) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]

We experimentally studied the dynamics of optically excited hotspots in current-carrying WSi superconducting nanowires as a function of bias current, bath temperature, and excitation wavelength. We observed that the hotspot relaxation time depends on bias current, temperature, and wavelength. We explained this effect with a model based on quasiparticle recombination, which provides insight into the quasiparticle dynamics of superconductors. © 2016 American Physical Society.

We experimentally studied the dynamics of optically excited hotspots in current-carrying WSi superconducting nanowires as a function of bias current, bath temperature, and excitation wavelength. We observed that the hotspot relaxation time depends on bias current, temperature, and wavelength. We explained this effect with a model based on quasiparticle recombination, which provides insight into the quasiparticle dynamics of superconductors. © 2016 American Physical Society.

BACKGROUND: Most patients with post-stroke dysphagia are also affected by facial dysfunction in all four facial quadrants. Intraoral stimulation can successfully treat post-stroke dysphagia, but its effect on post-stroke facial dysfunction remains unknown. OBJECTIVE: This study aimed to investigate whether intraoral stimulation after stroke has simultaneous effects on facial dysfunction in the contralateral lower facial quadrant and in the other three facial quadrants, on lip force, and on dysphagia. METHODS: Thirty-one stroke patients were treated with intraoral stimulation and assessed with a facial activity test, lip force test, and swallowing capacity test at three time-points: before treatment, at the end of treatment, and at late follow-up (over one year after the end of treatment). RESULTS: Facial activity, lip force, and swallowing capacity scores were all improved between baseline and the end of treatment (P < 0.001 for each), with these improvements remaining at late follow-up. Baseline and treatment data did not significantly differ between patients treated short and late after stroke. CONCLUSIONS: Treatment with intraoral stimulation significantly improved post-stroke dysfunction in all four facial quadrants, swallowing capacity, and lip force even in cases of long-standing post-stroke dysfunction. Furthermore, such improvement remained for over one year after the end of treatment.

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect., Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

BACKGROUND: Most patients with post-stroke dysphagia are also affected by facial dysfunction in all four facial quadrants. Intraoral stimulation can successfully treat post-stroke dysphagia, but its effect on post-stroke facial dysfunction remains unknown. OBJECTIVE: This study aimed to investigate whether intraoral stimulation after stroke has simultaneous effects on facial dysfunction in the contralateral lower facial quadrant and in the other three facial quadrants, on lip force, and on dysphagia. METHODS: Thirty-one stroke patients were treated with intraoral stimulation and assessed with a facial activity test, lip force test, and swallowing capacity test at three time-points: before treatment, at the end of treatment, and at late follow-up (over one year after the end of treatment). RESULTS: Facial activity, lip force, and swallowing capacity scores were all improved between baseline and the end of treatment (P less than 0.001 for each), with these improvements remaining at late follow-up. Baseline and treatment data did not significantly differ between patients treated short and late after stroke. CONCLUSIONS: Treatment with intraoral stimulation significantly improved post-stroke dysfunction in all four facial quadrants, swallowing capacity, and lip force even in cases of long-standing post-stroke dysfunction. Furthermore, such improvement remained for over one year after the end of treatment.

Quantum key distribution (QKD) enables participants to exchange secret information over long distances with unconditional security. However, the performance of today's QKD systems is subject to hardware limitations, such as those of available nonclassical-light sources and single-photon detectors. By encoding photons in high-dimensional states, the rate of generating secure information under these technical constraints can be maximized. Here, we demonstrate a complete time-energy entanglement-based QKD system with proven security against the broad class of arbitrary collective attacks. The security of the system is based on nonlocal dispersion cancellation between two time-energy entangled photons. This resource-efficient QKD system is implemented at telecommunications wavelength, is suitable for optical fiber and free-space links, and is compatible with wavelength-division multiplexing., United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program (Grant W911NF-10-1-0416)), National Science Foundation (U.S.). Integrative Graduate Education and Research Traineeship (Grant DGE-1069420)

Conventional quantum key distribution (QKD) typically uses binary encoding based on photon polarization or time-bin degrees of freedom and achieves a key capacity of at most one bit per photon. Under photon-starved conditions the rate of detection events is much lower than the photon generation rate, because of losses in long distance propagation and the relatively long recovery times of available single-photon detectors. Multi-bit encoding in the photon arrival times can be beneficial in such photon-starved situations. Recent security proofs indicate high-dimensional encoding in the photon arrival times is robust and can be implemented to yield high secure throughput. In this work we demonstrate entanglement-based QKD with high-dimensional encoding whose security against collective Gaussian attacks is provided by a high-visibility Franson interferometer. We achieve unprecedented key capacity and throughput for an entanglement-based QKD system because of four principal factors: Franson interferometry that does not degrade with loss; error correction coding that can tolerate high error rates; optimized time–energy entanglement generation; and highly efficient WSi superconducting nanowire single-photon detectors. The secure key capacity yields as much as 8.7 bits per coincidence. When optimized for throughput we observe a secure key rate of 2.7 Mbit s[superscript −1] after 20 km fiber transmission with a key capacity of 6.9 bits per photon coincidence. Our results demonstrate a viable approach to high-rate QKD using practical photonic entanglement and single-photon detection technologies., United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program Grant W911NF-10-1-0416)