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1.
Rev Sci Instrum ; 92(12): 124502, 2021 Dec 01.
Artículo en Inglés | MEDLINE | ID: mdl-34972408

RESUMEN

Axion dark matter experiment ultra-low noise haloscope technology has enabled the successful completion of two science runs (1A and 1B) that looked for dark matter axions in the 2.66-3.1 µeV mass range with Dine-Fischler-Srednicki-Zhitnisky sensitivity [Du et al., Phys. Rev. Lett. 120, 151301 (2018) and Braine et al., Phys. Rev. Lett. 124, 101303 (2020)]. Therefore, it is the most sensitive axion search experiment to date in this mass range. We discuss the technological advances made in the last several years to achieve this sensitivity, which includes the implementation of components, such as the state-of-the-art quantum-noise-limited amplifiers and a dilution refrigerator. Furthermore, we demonstrate the use of a frequency tunable microstrip superconducting quantum interference device amplifier in run 1A, and a Josephson parametric amplifier in run 1B, along with novel analysis tools that characterize the system noise temperature.

2.
Phys Rev Lett ; 124(10): 101303, 2020 Mar 13.
Artículo en Inglés | MEDLINE | ID: mdl-32216421

RESUMEN

This Letter reports on a cavity haloscope search for dark matter axions in the Galactic halo in the mass range 2.81-3.31 µeV. This search utilizes the combination of a low-noise Josephson parametric amplifier and a large-cavity haloscope to achieve unprecedented sensitivity across this mass range. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics.

3.
Phys Rev Lett ; 120(4): 040505, 2018 Jan 26.
Artículo en Inglés | MEDLINE | ID: mdl-29437450

RESUMEN

Microwave squeezing represents the ultimate sensitivity frontier for superconducting qubit measurement. However, measurement enhancement has remained elusive, in part because integration with standard dispersive readout pollutes the signal channel with antisqueezed noise. Here we induce a stroboscopic light-matter coupling with superior squeezing compatibility, and observe an increase in the final signal-to-noise ratio of 24%. Squeezing the orthogonal phase slows measurement-induced dephasing by a factor of 1.8. This scheme provides a means to the practical application of squeezing for qubit measurement.

4.
Phys Rev Lett ; 112(17): 170501, 2014 May 02.
Artículo en Inglés | MEDLINE | ID: mdl-24836225

RESUMEN

The creation of a quantum network requires the distribution of coherent information across macroscopic distances. We demonstrate the entanglement of two superconducting qubits, separated by more than a meter of coaxial cable, by designing a joint measurement that probabilistically projects onto an entangled state. By using a continuous measurement scheme, we are further able to observe single quantum trajectories of the joint two-qubit state, confirming the validity of the quantum Bayesian formalism for a cascaded system. Our results allow us to resolve the dynamics of continuous projection onto the entangled manifold, in quantitative agreement with theory.

5.
Phys Rev Lett ; 112(12): 120501, 2014 Mar 28.
Artículo en Inglés | MEDLINE | ID: mdl-24724636

RESUMEN

We report the observation of strong coupling of a macroscopic ensemble of ∼1016 Fe8 molecular nanomagnets to the resonant mode of a microwave cavity. We use millimeter-wave spectroscopy to measure the splitting of the system's resonant frequency induced by the coupling between the spins and the cavity mode. The magnitude of this splitting is found to scale with √N, where N is the number of collectively coupled spins. We control N by changing the system's temperature and, thereby, the populations of the relevant spin energy levels. Strong coupling is observed for two distinct transitions between spin energy states. Our results indicate that at low temperatures nearly all of the spins in the sample couple with the cavity's resonant mode even though there is substantial inhomogeneous broadening of the Fe8 spin resonances.

6.
J Speech Lang Hear Res ; 42(3): 516-25, 1999 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-10391619

RESUMEN

The present study investigated physiological correlates of the time-intensity trading relationship in late components (N1, P2) of the auditory evoked potential. Late-potential and behavioral thresholds were estimated in five normal-hearing, young adult participants for 1000- and 4000-Hz tone bursts having durations of 8, 16, 32, 64, and 128 ms. The results showed that late-potential thresholds decreased by an average of 24 dB for 1000-Hz conditions and 18 dB for 4000-Hz conditions. Behavioral thresholds also improved by about 22 dB and 18 dB for 1000-Hz and 4000-Hz conditions, respectively. The slope of improvement for both late-potential and behavioral thresholds was on the order of -4 to -6 dB per doubling of stimulus duration, depending on stimulus frequency. Stimulus duration also influenced latency and amplitude measures of the N1 and P2 components such that response latency decreased and amplitude increased as stimulus duration increased. The present results demonstrate a time-intensity trading relationship in components of the late potentials that is consistent with previous psychophysical and physiological data.


Asunto(s)
Potenciales Evocados Auditivos/fisiología , Pruebas de Impedancia Acústica , Adulto , Umbral Auditivo/fisiología , Femenino , Audición/fisiología , Humanos , Masculino , Factores de Tiempo
7.
Hear Res ; 127(1-2): 119-28, 1999 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-9925023

RESUMEN

The aim of this study was to evaluate the reduction in 2f1-f2 distortion product otoacoustic emission (DPOAE) amplitude resulting from prolonged noise exposures. A group of five chinchillas was exposed continuously to an octave-band noise centered at 4.0 kHz for a total of 42 days, 6 days at each of seven exposure levels. Exposure level increased in 8-dB steps from 48 to 96 dB SPL. DPOAE input-output (I/O) functions were measured at octave intervals over a range of primary tone f2 frequencies between 1.2 and 9.6 kHz. Measurements were obtained (1) pre-exposure, (2) during days 3-6 of each 6-day exposure, and (3) 4 weeks after the final exposure. Continuous noise exposure caused a reduction in DPOAE amplitude that was greatest at f2 frequencies within and above (3.4-6.8 kHz) the octave-band noise exposure. For these f2 frequencies, DPOAE amplitudes decreased as exposure level increased up to approximately 72-80 dB SPL; higher exposure levels failed to cause any further reduction in DPOAE amplitude. The noise level at which DPOAE amplitude began to decrease was approximately 50 dB SPL. Above this critical level, DPOAE amplitude decreased 1.3 dB for every dB increase in noise level up to approximately 75 dB SPL.


Asunto(s)
Ruido/efectos adversos , Emisiones Otoacústicas Espontáneas/fisiología , Animales , Umbral Auditivo/fisiología , Chinchilla , Modelos Animales de Enfermedad , Femenino , Células Ciliadas Auditivas Internas/lesiones , Células Ciliadas Auditivas Internas/fisiopatología , Células Ciliadas Auditivas Externas/lesiones , Células Ciliadas Auditivas Externas/fisiopatología , Pérdida Auditiva Provocada por Ruido/etiología , Pérdida Auditiva Provocada por Ruido/fisiopatología , Masculino , Factores de Tiempo
9.
J Neurophysiol ; 80(2): 863-81, 1998 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-9705474

RESUMEN

We evaluated two hypothetical codes for sound-source location in the auditory cortex. The topographical code assumed that single neurons are selective for particular locations and that sound-source locations are coded by the cortical location of small populations of maximally activated neurons. The distributed code assumed that the responses of individual neurons can carry information about locations throughout 360 degrees of azimuth and that accurate sound localization derives from information that is distributed across large populations of such panoramic neurons. We recorded from single units in the anterior ectosylvian sulcus area (area AES) and in area A2 of alpha-chloralose-anesthetized cats. Results obtained in the two areas were essentially equivalent. Noise bursts were presented from loudspeakers spaced in 20 degrees intervals of azimuth throughout 360 degrees of the horizontal plane. Spike counts of the majority of units were modulated >50% by changes in sound-source azimuth. Nevertheless, sound-source locations that produced greater than half-maximal spike counts often spanned >180 degrees of azimuth. The spatial selectivity of units tended to broaden and, often, to shift in azimuth as sound pressure levels (SPLs) were increased to a moderate level. We sometimes saw systematic changes in spatial tuning along segments of electrode tracks as long as 1.5 mm but such progressions were not evident at higher sound levels. Moderate-level sounds presented anywhere in the contralateral hemifield produced greater than half-maximal activation of nearly all units. These results are not consistent with the hypothesis of a topographic code. We used an artificial-neural-network algorithm to recognize spike patterns and, thereby, infer the locations of sound sources. Network input consisted of spike density functions formed by averages of responses to eight stimulus repetitions. Information carried in the responses of single units permitted reasonable estimates of sound-source locations throughout 360 degrees of azimuth. The most accurate units exhibited median errors in localization of <25 degrees, meaning that the network output fell within 25 degrees of the correct location on half of the trials. Spike patterns tended to vary with stimulus SPL, but level-invariant features of patterns permitted estimates of locations of sound sources that varied through 20-dB ranges. Sound localization based on spike patterns that preserved details of spike timing consistently was more accurate than localization based on spike counts alone. These results support the hypothesis that sound-source locations are represented by a distributed code and that individual neurons are, in effect, panoramic localizers.


Asunto(s)
Corteza Auditiva/fisiología , Redes Neurales de la Computación , Localización de Sonidos/fisiología , Potenciales de Acción/fisiología , Animales , Gatos , Potenciales Evocados Auditivos/fisiología , Femenino , Lateralidad Funcional/fisiología , Masculino , Neuronas Aferentes/fisiología , Presión , Detección de Reclutamiento Audiológico
10.
Hear Res ; 119(1-2): 135-41, 1998 May.
Artículo en Inglés | MEDLINE | ID: mdl-9641326

RESUMEN

The purpose of the present study was to measure the change in threshold as a function of stimulus duration in single auditory nerve fibers. Thresholds were measured at each neuron's characteristic frequency (CF) for eight stimulus durations ranging from 8 to 1024 ms. Using an adaptive, two-interval, forced-choice threshold-tracking procedure with a 2-down, 1-up rule, thresholds were estimated based on a decision criterion of one spike or greater difference between tone and no-tone intervals. The results showed that mean thresholds decreased with increasing stimulus duration by approximately 14.6 dB over the range of durations tested. Analysis of group and individual data showed that thresholds decreased by approximately 6-7 dB per decade of duration. The slope of threshold improvement decreased systematically with increasing CF, consistent with previous physiological and psychophysical data.


Asunto(s)
Umbral Auditivo/fisiología , Fibras Nerviosas/fisiología , Nervio Vestibulococlear/fisiología , Estimulación Acústica , Animales , Chinchilla , Potenciales Evocados Auditivos del Tronco Encefálico/fisiología
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