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Reference : UMR5130-DALALO-005
Workplace : LE BOURGET DU LAC
Date of publication : Monday, November 16, 2020
Type of Contract : FTC Technical / Administrative
Contract Period : 12 months
Expected date of employment : 1 February 2021
Proportion of work : Full time
Remuneration : Remuneration :Raw salary : 2088€ à 2206€ / month depending on experience
Desired level of education : 5-year university degree
Experience required : 1 to 4 years
The Laboratory of Microwave and Characterization (IMEP-LAHC, CNRS UMR 5130) of Université Savoie Mont Blanc located in the French Alps area develops activities about superconductor electronics that comprise the development of analogue sensors using the properties of quantum mechanics to reach ultimate sensitivity, and the studies of ultrafast energy-efficient superconducting digital circuits that can work with clock frequencies of several tens of GHz, based on the Single-Flux Quantum (SFQ) technology. The combination of analogue and digital superconductor electronics based on the same fabrication technology leads to mixed-signal circuits that can be used in a range of applications for which a fast and efficient processing can be performed directly on-chip at cryogenic temperature, close to the sensors. This technology is interesting when either high energy efficiency, high bandwidth or on-chip control and readout of complex arrays of quantum-accurate sensors is required. Sensors can be of magnetic type, like Superconducting Quantum Interference Devices (SQUIDs), or of microwave types like Kinetic Inductance Detectors (KIDs), THz quantum-accurate Superconductor-Insulator-Superconductor (SIS) heterodyne sensors, Transition Edge Sensors (TES), used for instance in radio-astronomy at the focal point of ground-, balloon- and space-based telescopes. This technology can also be used to simplify the readout and control of Quantum Bits (Qu-bits) for quantum computing applications, or to detect single photons based on Superconducting Nanowire Single-Photon Detector (SNSPDs), also used for quantum cryptography.
In this context superconductor electronics activity conducted in close collaboration with several laboratories and research centers, is focused on:
• the study, design and experimental characterization of high and low critical temperature digital and analogue superconductor circuits: influence of magnetic field, temperature, THz frequency behavior, study of new devices and principles ;
• the development of demonstrators based on superconductor mixed-signal circuits for applications in space telecommunications and in geophysics ;
• the development of open-source software tools for the design and characterization of complex digital circuits, analogue systems (including THz superconducting sensors) and mixed-signal circuits.
In the frame of the ColdFlux project developed between groups located in the United States of America, South Africa, Japan and France, we study the electrical, thermal and microwave properties of superconducting digital circuits. The work is focused on the development of a Multiphysics approach to predict the behavior of circuits and build advanced SPICE-based models as well as dynamic libraries and TCAD modules to help the designer. All developed software will be open-source, compatible with tools developed by other partners of the project and ultimately available for other communities. The development of test benches based on the design of specific superconducting digital circuits is planned to verify the proper operation of the suite of software tools.
The first objective of the work is to extend the capabilities of a C++ software developed under the Qt platform to predict the behavior of Josephson junctions in presence of quasiparticle currents. So far existing software for digital electronics only take into account the supercurrents for digital applications. This is sufficient for simple circuits at not too high frequencies but the model becomes inaccurate in other conditions. The current software works in frequency domain and predicts the behavior in general conditions. The next step is to achieve the calculations in presence of a microwave environment by using the harmonic balance method. From this implementation it will be possible to tune and optimize the performance of the device under different external conditions to develop different non-linear devices interesting for future high-frequency applications. The other step is about finding the best algorithm to simulate performances in the time domain. Once this is achieved this software will be used to study a set of new non-linear devices for microwave applications whose results can be published. Fabrication will be planned in parallel to compare with simulation. Moreover the model extracted from the software will be transferred to the South African team of the project to be incorporated in the design software for digital circuits.
The second objective is to extract the parameters of Josephson junctions to feed the software mentioned above with physical parameters coming the fabrication process by using the outcome of the FLOOXS TCAD software developed by the University of Florida with whom we collaborate. The objective is to handle their open-source software and interface it with our own developed software to make the integration seamless and be able to predict with accuracy the behavior of specific microwave circuits. The global software platform integrating the TCAD code and the microwave simulation software is existing but will need to be improved to make it user-friendly in order to perform fast simulations of new circuits.
Excellent skills are expected in two fields:
- computer science with C/C++ coding on the Qt multiplatform environment. A set of other tools based on Matlab, Layout Editor, Comsol, Inductex, JSIM and JoSIM will be used;
- mathematics skills are also necessary to develop mathematical algorithms and numerical analysis techniques regarding the development of new synthesis methods to optimize the design of analogue and digital superconductor circuits and include artificial intelligence kernels. Physics skills are also an asset to succeed faster in the tasks, though in-house mentoring will be provided in this field.
The context of this position is international with strong interactions required with US, South African, Japanese, Italian, Turkish and Ukrainian groups, either virtually during the Covid period or in person as soon as the situation improves. Writing of monthly reports is expected as well as publications in international journals. Attendance to international conferences, workshops and summer schools is also encouraged if the health context allows it. Locally the candidate will need to interact within a team of four to six people including post-doctoral research, PhD students and master students.
Constraints and risks
No experimental work is required. We plan as much as possible to hold weekly meetings, either virtually or in presence in the laboratory if the situations allows it.
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