scalable-quantum-integrated-circuits-on-superconducting-two

Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface ...

University of Cambridge

 We report the experimental evidence for the formation of multi-quantum dots in a hydrogenated single-layer graphene flake. The existence of multi-quantum dots is supported by the low-temperature measurements on a field effect transistor structure device. The resulting Coulomb blockade diamonds shown in the color scale plot together with the number of Coulomb peaks exhibit the characteristics of the so-called 'stochastic Coulomb blockade'. A possible explanation for the formation of the multi-quantum dots, which is not observed in pristine graphene to date, was attributed to the impurities and defects unintentionally decorated on a single-layer graphene flake which was not treated with the thermal annealing process. Graphene multi-quantum dots developed around impurities and defect sites during the hydrogen plasma exposure process.

Evidence for formation of multi-quantum dots in hydrogenated graphene.

A superconducting hard gap in hybrid superconductor-semiconductor devices has been found to be necessary to access topological superconductivity that hosts Majorana modes (non-Abelian excitation). This requires the formation of homogeneous and barrier-free interfaces between the superconductor and semiconductor. Here, a new platform is reported for topological superconductivity based on hybrid Nb-In Ga As-quantum-well-Nb that results in hard superconducting gap detection in symmetric, planar, and ballistic Josephson junctions. It is shown that with careful etching, sputtered Nb films can make high-quality and transparent contacts to the In Ga As quantum well, and the differential resistance and critical current measurements of these devices are discussed as a function of temperature and magnetic field. It is demonstrated that proximity-induced superconductivity in the In Ga As-quantum-well 2D electron gas results in the detection of a hard gap in four out of seven junctions on a chip with critical current values of up to 0.2 µA and transmission probabilities of >0.96. The results, together with the large g-factor and Rashba spin-orbit coupling in In Ga As quantum wells, which indeed can be tuned by the indium composition, suggest that the Nb-In Ga As-Nb system can be an excellent candidate to achieve topological phase and to realize hybrid topological superconducting devices.

Article	Year
Evidence for formation of multi-quantum dots in hydrogenated graphene. Nanoscale research letters\| PubMed ID: 22898058	2012
On-Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb-In Ga As-Quantum-Well-Nb Josephson Junctions. Advanced materials (Deerfield Beach, Fla.)\| PubMed ID: 28804969	2017

Reuben Puddy

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