12 research outputs found
Superconducting Nanostructures for Quantum Detection of Electromagnetic Radiation
In this thesis, superconducting nanostructures for quantum detection of electromagnetic
radiation are studied. In this regard, electrodynamics of topological excitations in 1D
superconducting nanowires and 2D superconducting nanostrips is investigated. Topological excitations in superconducting nanowires and nanostrips lead to crucial deviation from the bulk properties. In 1D superconductors, topological excitations are phase slippages of the order parameter in which the magnitude of the order parameter locally drops to zero and the phase jumps by integer multiple of 2\pi. We investigate the effect of high-frequency ïŹeld on 1D superconducting nanowires and derive the complex conductivity. Our study reveals that the rate of the quantum phase slips (QPSs) is exponentially enhanced under high-frequency irradiation. Based on this ïŹnding, we propose an energy-resolving terahertz radiation detector using superconducting nanowires. In superconducting nanostrips, topological ïŹuctuations are the magnetic vortices. The motion of magnetic vortices result in dissipative processes that limit the efficiency of devices using superconducting nanostrips.
It will be shown that in a multi-layer structure, the potential barrier for vortices to penetrate inside the structure is elevated. This results in significant reduction in dissipative
process. In superconducting nanowire single photon detectors (SNSPDs), vortex motion
results in dark counts and reduction of the critical current which results in low efficiency
in these detectors. Based on this ïŹnding, we show that a multi-layer SNSPD is capable of approaching characteristics of an ideal single photon detector in terms of the dark count and quantum efficiency. It is shown that in a multi-layer SNSPD the photon coupling
efficiency is dramatically enhanced due to the increase in the optical path of the incident
photon.4 month
Stimulated quantum phase slips from weak electromagnetic radiations in superconducting nanowires
We study the rate of quantum phase slips in an ultranarrow superconducting
nanowire exposed to weak electromagnetic radiations. The superconductor is in
the dirty limit close to the superconducting-insulating transition, where
fluxoids move in strong dissipation. We use a semiclassical approach and show
that external radiation stimulates a significant enhancement in the probability
of quantum phase slips. This can help to outline a new type of detector for
microwave to submillimetre radiations based on stimulated quantum phase slip
phenomenon.Comment: 10 pages, 9 figure
Dynamics of O(N) Model in a Strong Magnetic Background Field as a Modified Noncommutative Field Theory
In the presence of a strong magnetic field, the effective action of a
composite scalar field in an scalar O(N) model is derived using two different
methods. First, in the framework of worldline formalism, the 1PI n-point vertex
function for the composites is determined in the limit of strong magnetic
field. Then, the n-point effective action of the composites is calculated in
the regime of lowest Landau level dominance. It is shown that in the limit of
strong magnetic field, the results coincide and an effective field theory
arises which is comparable with the conventional noncommutative field theory.
In contrast to the ordinary case, however, the UV/IR mixing is absent in this
modified noncommutative field theory.Comment: Latex file, 19 pp, no figur
Matrix Theory of Type IIB Plane Wave from Membranes
We write down a maximally supersymmetric one parameter deformation of the
field theory action of Bagger and Lambert. We show that this theory on RxT^2 is
invariant under the superalgebra of the maximally supersymmetric Type IIB plane
wave. It is argued that this theory holographically describes the Type IIB
plane wave in the discrete light-cone quantization (DLCQ).Comment: 19 pages, harvmac; typos fixed and references added; one more
reference adde
Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices
One of the most challenging obstacles to realizing exascale computing is
minimizing the energy consumption of L2 cache, main memory, and interconnects
to that memory. For promising cryogenic computing schemes utilizing Josephson
junction superconducting logic, this obstacle is exacerbated by the cryogenic
system requirements that expose the technology's lack of high-density,
high-speed and power-efficient memory. Here we demonstrate an array of
cryogenic memory cells consisting of a non-volatile three-terminal magnetic
tunnel junction element driven by the spin Hall effect, combined with a
superconducting heater-cryotron bit-select element. The write energy of these
memory elements is roughly 8 pJ with a bit-select element, designed to achieve
a minimum overhead power consumption of about 30%. Individual magnetic memory
cells measured at 4 K show reliable switching with write error rates below
, and a 4x4 array can be fully addressed with bit select error rates
of . This demonstration is a first step towards a full cryogenic
memory architecture targeting energy and performance specifications appropriate
for applications in superconducting high performance and quantum computing
control systems, which require significant memory resources operating at 4 K.Comment: 10 pages, 6 figures, submitte