84 research outputs found
Timing performance of 30-nm-wide superconducting nanowire avalanche photodetectors
We investigated the timing jitter of superconducting nanowire avalanche
photodetectors (SNAPs, also referred to as cascade switching superconducting
single photon detectors) based on 30-nm-wide nanowires. At bias currents (IB)
near the switching current, SNAPs showed sub 35 ps FWHM Gaussian jitter similar
to standard 100 nm wide superconducting nanowire single-photon detectors. At
lower values of IB, the instrument response function (IRF) of the detectors
became wider, more asymmetric, and shifted to longer time delays. We could
reproduce the experimentally observed IRF time-shift in simulations based on an
electrothermal model, and explain the effect with a simple physical picture
Broadening the bandwidth of entangled photons: a step towards the generation of extremely short biphotons
We demonstrate a technique that allows to fully control the bandwidth of
entangled photons independently of the frequency band of interest and of the
nonlinear crystal. We show that this technique allows to generate nearly
transform-limited biphotons with almost one octave of bandwidth (hundreds of
THz) which corresponds to correlation times of just a few femtoseconds. The
presented method becomes an enabling tool for attosecond entangled-photons
quantum optics. The technique can also be used to generate paired photons with
a very high degree of entanglement.Comment: 4 page
Electrothermal feedback in superconducting nanowire single-photon detectors
We investigate the role of electrothermal feedback in the operation of
superconducting nanowire single-photon detectors (SNSPDs). It is found that the
desired mode of operation for SNSPDs is only achieved if this feedback is
unstable, which happens naturally through the slow electrical response
associated with their relatively large kinetic inductance. If this response is
sped up in an effort to increase the device count rate, the electrothermal
feedback becomes stable and results in an effect known as latching, where the
device is locked in a resistive state and can no longer detect photons. We
present a set of experiments which elucidate this effect, and a simple model
which quantitatively explains the results
Ultraslow propagation of matched pulses by four-wave mixing in an atomic vapor
We have observed the ultraslow propagation of matched pulses in nondegenerate
four-wave mixing in a hot atomic vapor. Probe pulses as short as 70 ns can be
delayed by a tunable time of up to 40 ns with little broadening or distortion.
During the propagation, a probe pulse is amplified and generates a conjugate
pulse which is faster and separates from the probe pulse before getting locked
to it at a fixed delay. The precise timing of this process allows us to
determine the key coefficients of the susceptibility tensor. The presence of
gain in this system makes this system very interesting in the context of
all-optical information processing.Comment: 5 pages, 4 figure
Superconducting microfabricated ion traps
We fabricate superconducting ion traps with niobium and niobium nitride and
trap single 88Sr ions at cryogenic temperatures. The superconducting transition
is verified and characterized by measuring the resistance and critical current
using a 4-wire measurement on the trap structure, and observing change in the
rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz
at 6 K and shows no significant change across the superconducting transition,
suggesting that anomalous heating is primarily caused by noise sources on the
surface. This demonstration of superconducting ion traps opens up possibilities
for integrating trapped ions and molecular ions with superconducting devices.Comment: 3 pages, 2 figure
Afterpulsing and instability in superconducting nanowire avalanche photodetectors
We investigated the reset time of superconducting nanowire avalanche photodetectors (SNAPs) based on 30 nm wide nanowires. We studied the dependence of the reset time of SNAPs on the device inductance and discovered that SNAPs can provide a speed-up relative to superconducting nanowire single-photon detectors with the same area but with some limitations: (1) Reducing the series inductance of SNAPs (necessary for the avalanche formation) could result in the detectors operating in an unstable regime, (2) a trade-off exists between maximizing the bias current margin and minimizing the reset time of SNAPs, and (3) reducing the reset time of SNAPs below ∼1 ns resulted in afterpulsing.United States. Intelligence Advanced Research Projects ActivityUnited States. Air Force (Air Force Contract No. FA8721-05-C-0002)United States. Dept. of Energy. Center for Excitonics (Award No. DE-SC0001088
Kinetic-inductance-limited reset time of superconducting nanowire photon counters
We investigate the recovery of superconducting NbN-nanowire photon counters
after detection of an optical pulse at a wavelength of 1550 nm, and present a
model that quantitatively accounts for our observations. The reset time is
found to be limited by the large kinetic inductance of these nanowires, which
forces a tradeoff between counting rate and either detection efficiency or
active area. Devices of usable size and high detection efficiency are found to
have reset times orders of magnitude longer than their intrinsic photoresponse
time.Comment: Submitted to Applied Physics Letter
Experimental study of the frequency correlation of space-time entangled photons
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 57-58).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Space-time entangled photons generated from a continuous-wave parametric downconverter have a well defined sum-frequency despite having individual broad bandwidths. The narrowband frequency correlation that results from this well defined sum-frequency is examined experimentally. The measurements use degenerate, 1.55 [mu]m photon pairs that are also suitable for fiber-based quantum communication protocols. Techniques for optimizing the pair generation rate, the detector and coincidence circuit parameters and the fiber coupling of down-converted light are also presented. A strong frequency correlation is observed using ~0.5 nm bandpass filters to measure the frequencies of entangled photons with >100 nm individual bandwidths.by Eric A. Dauler.M.Eng
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