QUEST · QUantum-device Engineering with novel STates of matter

QUantum-device Engineering with novel STates of matter

The overarching goal of this project is to employ novel states of matter for the development of new devices for quantum technologies, optoelectronics and ultrafast nanoelectronics. Speeding up and miniaturization of the existing electronics are approaching their physical limits. Novel states of mater are a rapidly growing field of science including quantum condensates and superconductors. One of the topics in the current project explores devices based on condensates of exciton-polaritons in semiconductors, representing both: ultrafast low-dissipation electronics due to their light-matter superfluid properties, as well as extremely nonlinear optics useful for quantum photonics. The first objective of the project related to this topic is: Investigation of exciton–polariton condensate ultrafast dynamics, and implementation of fast switching devices and circuits. Several important results have been achieved on this objective: Ultra-fast Stark-induced polaritonic switches were proposed and studied theoretically, and enhanced coherence between condensates formed resonantly at different times was demonstrated experimentally. Strong light-matter coupling in a GaAs/AlGaAs microcavity was modulated using intense ultrashort laser pulses tuned below the exciton resonance. The exciton is transiently decoupled from the light field for the duration of the pulse, which we chose longer (1500fs) or shorter (225fs) than the Rabi cycle time of 500 fs, resulting in distinctly different line shapes in ultrafast reflection measurements. Another approach in the project, which can provide a new direction in optoelectronic devices, is based on combining superconductors with semiconductors. The project takes advantage of the recent progress in high-temperature superconductors, which makes these technologies significantly more practical. This topic is addressed in the second objective: Experimental and theoretical study of high-temperature superconductor optoelectronic devices. A number of advancements were achieved in this direction: Novel superconductor-semiconductor optoelectronics devices were proposed and analyzed including entanglement sources and superconducting two-photon amplifiers. Photon assisted tunneling in high-Tc superconductor-semiconductor optoelectronics devices was demonstrated experimentally. A new concept of efficient full Bell-state analysis based on photon-pair detection in a semiconductor-superconductor structure was proposed and analyzed. A new theoretical approach for modelling a wide range of semiconductor-superconductor structures was developed, showing that Andreev reflection can be significantly enhanced through resonant tunneling. A high-temperature nanoscale super-Schottky diode based on a superconducting tunnel junction of pulsed-laser-deposited YBCO on GaN thin films was demonstrated experimentally. Lately, a novel paradigm for finding new properties in the solid state has emerged - through the sudden change in topological invariants rather than breaking of symmetries. These topological phases of matter have been demonstrated to exist at the surface of some materials with strong spin-orbit coupling, revealing novel physical properties, including dissipationless spin currents with potential applications in spintronics and quantum technologies. A part of the current research focuses on devices based on proximity-induced high-temperature superconductivity in such topological insulators. This proximity effect has been predicted recently to produce the elusive Majorana fermion, which is of great interest for condensed-matter physics and quantum computation and for the development of new quantum technologies and ultrafast low-power electronics. This direction is addressed by the third objective: Realization of novel high-temperature topological superconductor devices and characterization by electrical and optical measurements. Significant progress was achieved in this direction. A new excitation at the interface between a high-Tc superconductor BSCCO and a topological insulator Bi2Te2Se was demonstrated as well as ultrafast optical control of spin injection into topological insulator surface states. The controversy over the proximity effect between topological materials and high-T c superconductors was addressed experimentally, showing that the Fermi surface mismatch does not hinder the ability to form transparent interfaces.

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