2,139 research outputs found
Hall Effect Gyrators and Circulators
The electronic circulator, and its close relative the gyrator, are invaluable
tools for noise management and signal routing in the current generation of
low-temperature microwave systems for the implementation of new quantum
technologies. The current implementation of these devices using the Faraday
effect is satisfactory, but requires a bulky structure whose physical dimension
is close to the microwave wavelength employed. The Hall effect is an
alternative non-reciprocal effect that can also be used to produce desired
device functionality. We review earlier efforts to use an ohmically-contacted
four-terminal Hall bar, explaining why this approach leads to unacceptably high
device loss. We find that capacitive coupling to such a Hall conductor has much
greater promise for achieving good circulator and gyrator functionality. We
formulate a classical Ohm-Hall analysis for calculating the properties of such
a device, and show how this classical theory simplifies remarkably in the
limiting case of the Hall angle approaching 90 degrees. In this limit we find
that either a four-terminal or a three-terminal capacitive device can give
excellent circulator behavior, with device dimensions far smaller than the a.c.
wavelength. An experiment is proposed to achieve GHz-band gyration in
millimetre (and smaller) scale structures employing either semiconductor
heterostructure or graphene Hall conductors. An inductively coupled scheme for
realising a Hall gyrator is also analysed.Comment: 18 pages, 15 figures, ~5 MB. V3: sections V-VIII revisited plus other
minor changes, Fig 2 added. Submitted to PR
Dicke simulators with emergent collective quantum computational abilities
Using an approach inspired from Spin Glasses, we show that the multimode
disordered Dicke model is equivalent to a quantum Hopfield network. We propose
variational ground states for the system at zero temperature, which we
conjecture to be exact in the thermodynamic limit. These ground states contain
the information on the disordered qubit-photon couplings. These results lead to
two intriguing physical implications. First, once the qubit-photon couplings
can be engineered, it should be possible to build scalable pattern-storing
systems whose dynamics is governed by quantum laws. Second, we argue with an
example how such Dicke quantum simulators might be used as a solver of "hard"
combinatorial optimization problems.Comment: 5+2 pages, 2 figures. revisited in the exposition and supplementary
added. Comments are welcom
Current-controlled light scattering and asymmetric plasmon propagation in graphene
We demonstrate that plasmons in graphene can be manipulated using a DC
current. A source-drain current lifts the forward/backward degeneracy of the
plasmons, creating two modes with different propagation properties parallel and
antiparallel to the current. We show that the propagation length of the plasmon
propagating parallel to the drift current is enhanced, while the propagation
length for the antiparallel plasmon is suppressed. We also investigate the
scattering of light off graphene due to the plasmons in a periodic dielectric
environment and we find that the plasmon resonance separates in two peaks
corresponding to the forward and backward plasmon modes. The narrower linewidth
of the forward propagating plasmon may be of interest for refractive index
sensing and the DC current control could be used for the modulation of
mid-infrared electromagnetic radiation.Comment: 5 pages, 5 figure
Optical signatures of nonlocal plasmons in graphene
We theoretically investigate under which conditions nonlocal plasmon response
in monolayer graphene can be detected. To this purpose, we study optical
scattering off graphene plasmon resonances coupled using a subwavelength
dielectric grating. We compute the graphene conductivity using the Random Phase
Approximation (RPA) obtaining a nonlocal conductivity and we calculate the
optical scattering of the graphene-grating structure. We then compare this with
the scattering amplitudes obtained if graphene is modeled by the local RPA
conductivity commonly used in the literature. We find that the graphene plasmon
wavelength calculated from the local model may deviate up to from the
more accurate nonlocal model in the small-wavelength (large-) regime. We
also find substantial differences in the scattering amplitudes obtained from
the two models. However, these differences in response are pronounced only for
small grating periods and low temperatures compared to the Fermi temperature.Comment: Accepted for publication in Physical Review B. 15 pages, 9 figure
High-sensitivity plasmonic refractive index sensing using graphene
We theoretically demonstrate a high-sensitivity, graphene-plasmon based
refractive index sensor working in the mid-infrared at room temperature. The
bulk figure of merit of our sensor reaches values above , but the key
aspect of our proposed plasmonic sensor is its surface sensitivity which we
examine in detail. We have used realistic values regarding doping level and
electron relaxation time, which is the limiting factor for the sensor
performance. Our results show quantitatively the high performance of
graphene-plasmon based refractive index sensors working in the mid-infrared.Comment: This is an author-created, un-copyedited version of an article
accepted for publication/published in 2DMaterials. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The Version of Record is available online at
https://doi.org/10.1088/2053-1583/aa70f
Laser Based Underwater Communication Systems
We report on recent progress in the field of visible light communications including direct modulation of blue laser devices at data rates beyond 10 Gbit/s, and the transmission of 2.5 Gbit/s OOK data through water. We also discuss the advantages of operating with single mode laser devices and matched filtering at the receiver in the context of applications with significant solar background. The system performance for two types of direct-detection receivers, a PIN detector and less conventional silicon Photomultiplier technology will be presented
PyGNA:A unified framework for geneset network analysis
Input data and results for the manuscript "PyGNA: a unified framework for geneset network analysis".
Manifest files describe the content of each file.This work has been supported by the Wellcome Trust Seed Award in Science (207769/A/17/Z) to G.S
Development and Validation of on-board systems control laws
Purpose - The purpose of this paper is to describe the tool and procedure developed in order to design the control laws of several UAV (Unmanned Aerial Vehicle) sub-systems. The authors designed and developed the logics governing: landing gear, nose wheel steering, wheel braking, and fuel system. Design/methodology/approach - This procedure is based on a general purpose, object-oriented, simulation tool. The development method used is based on three-steps. The main structure of the control laws is defined through flow charts; then the logics are ported to ANSI-C programming language; finally the code is implemented inside the status model. The status model is a Matlab-Simulink model, which uses an embedded Matlab-function to model the FCC (Flight Control Computer). The core block is linked with the components, but cannot access their internal model. Interfaces between FCCs and system components in the model reflect real system ones. Findings - The user verifies systems' reactions in real time, through the status model. Using block-oriented approach, development of the control laws and integration of several systems is faster. Practical implications - The tool aims to test and validate the control laws dynamically, helping specialists to find out odd logics or undesired responses, during the pre-design. Originality/value - The development team can test and verify the control laws in various failure scenarios. This tool allows more reliable and effective logics to be produced, which can be directly used on the system
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