33,576 research outputs found
Detection of zeptojoule microwave pulses using electrothermal feedback in proximity-induced Josephson junctions
We experimentally investigate and utilize electrothermal feedback in a
microwave nanobolometer based on a normal-metal
(\mbox{Au}_{x}\mbox{Pd}_{1-x}) nanowire with proximity-induced
superconductivity. The feedback couples the temperature and the electrical
degrees of freedom in the nanowire, which both absorbs the incoming microwave
radiation, and transduces the temperature change into a radio-frequency
electrical signal. We tune the feedback in situ and access both positive and
negative feedback regimes with rich nonlinear dynamics. In particular, strong
positive feedback leads to the emergence of two metastable electron temperature
states in the millikelvin range. We use these states for efficient threshold
detection of coherent 8.4 GHz microwave pulses containing approximately 200
photons on average, corresponding to 1.1 \mbox{ zJ} \approx 7.0 \mbox{ meV}
of energy
Noisy pre-processing facilitating a photonic realisation of device-independent quantum key distribution
Device-independent quantum key distribution provides security even when the
equipment used to communicate over the quantum channel is largely
uncharacterized. An experimental demonstration of device-independent quantum
key distribution is however challenging. A central obstacle in photonic
implementations is that the global detection efficiency, i.e., the probability
that the signals sent over the quantum channel are successfully received, must
be above a certain threshold. We here propose a method to significantly relax
this threshold, while maintaining provable device-independent security. This is
achieved with a protocol that adds artificial noise, which cannot be known or
controlled by an adversary, to the initial measurement data (the raw key).
Focusing on a realistic photonic setup using a source based on spontaneous
parametric down conversion, we give explicit bounds on the minimal required
global detection efficiency.Comment: 5+16 pages, 4 figure
Three fermions in a box at the unitary limit: universality in a lattice model
We consider three fermions with two spin components interacting on a lattice
model with an infinite scattering length. Low lying eigenenergies in a cubic
box with periodic boundary conditions, and for a zero total momentum, are
calculated numerically for decreasing values of the lattice period. The results
are compared to the predictions of the zero range Bethe-Peierls model in
continuous space, where the interaction is replaced by contact conditions. The
numerical computation, combined with analytical arguments, shows the absence of
negative energy solution, and a rapid convergence of the lattice model towards
the Bethe-Peierls model for a vanishing lattice period. This establishes for
this system the universality of the zero interaction range limit.Comment: 6 page
Measurement of Scattering Rate and Minimum Conductivity in Graphene
The conductivity of graphene samples with various levels of disorder is
investigated for a set of specimens with mobility in the range of
cm/V sec. Comparing the experimental data with the
theoretical transport calculations based on charged impurity scattering, we
estimate that the impurity concentration in the samples varies from cm. In the low carrier density limit, the conductivity exhibits
values in the range of , which can be related to the residual
density induced by the inhomogeneous charge distribution in the samples. The
shape of the conductivity curves indicates that high mobility samples contain
some short range disorder whereas low mobility samples are dominated by long
range scatterers.Comment: 4 pages 4 figure
SU(3) Quantum Interferometry with single-photon input pulses
We develop a framework for solving the action of a three-channel passive
optical interferometer on single-photon pulse inputs to each channel using
SU(3) group-theoretic methods, which can be readily generalized to higher-order
photon-coincidence experiments. We show that features of the coincidence plots
vs relative time delays of photons yield information about permanents,
immanants, and determinants of the interferometer SU(3) matrix
Predictable Disruption Tolerant Networks and Delivery Guarantees
This article studies disruption tolerant networks (DTNs) where each node
knows the probabilistic distribution of contacts with other nodes. It proposes
a framework that allows one to formalize the behaviour of such a network. It
generalizes extreme cases that have been studied before where (a) either nodes
only know their contact frequency with each other or (b) they have a perfect
knowledge of who meets who and when. This paper then gives an example of how
this framework can be used; it shows how one can find a packet forwarding
algorithm optimized to meet the 'delay/bandwidth consumption' trade-off:
packets are duplicated so as to (statistically) guarantee a given delay or
delivery probability, but not too much so as to reduce the bandwidth, energy,
and memory consumption.Comment: 9 page
Bond-Propagation Algorithm for Thermodynamic Functions in General 2D Ising Models
Recently, we developed and implemented the bond propagation algorithm for
calculating the partition function and correlation functions of random bond
Ising models in two dimensions. The algorithm is the fastest available for
calculating these quantities near the percolation threshold. In this paper, we
show how to extend the bond propagation algorithm to directly calculate
thermodynamic functions by applying the algorithm to derivatives of the
partition function, and we derive explicit expressions for this transformation.
We also discuss variations of the original bond propagation procedure within
the larger context of Y-Delta-Y-reducibility and discuss the relation of this
class of algorithm to other algorithms developed for Ising systems. We conclude
with a discussion on the outlook for applying similar algorithms to other
models.Comment: 12 pages, 10 figures; submitte
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