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

Abstract

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrierfree interface between two different materials is necessary. The S-Sm junction with high interface transparency will then facilitate the observation of the induced hard superconducting gap, which is the key requirement to access the topological phases (TPs) and observation of exotic quasiparticles such as Majorana zero modes (MZM) in hybrid systems. A material platform that can support observation of TPs and allows the realization of complex and branched geometries is therefore highly demanding in quantum processing and computing science and technology. Here, we introduce a two-dimensional material system and study the proximity induced superconductivity in semiconducting two-dimensional electron gas (2DEG) that is the basis of a hybrid quantum integrated circuit (QIC). The 2DEG is a 30 nm thick In 0.75 Ga 0.25 As quantum well that is buried between two In 0.75 Al 0.25 As barriers in a heterostructure. Niobium (Nb) films are used as the superconducting electrodes to form Nb-In 0.75 Ga 0.25 As-Nb Josephson junctions (JJs) that are symmetric, planar and ballistic. Two different approaches were used to form the JJs and QICs. The long junctions were fabricated photolithographically, but e-beam lithography was used for short junctions' fabrication. The coherent quantum transport measurements as a function of temperature in the presence/absence of magnetic field B are discussed. In both device fabrication approaches, the proximity induced superconducting properties were observed in the In 0.75 Ga 0.25 As 2DEG. It was found that e-beam lithographically patterned JJs of shorter lengths result in observation of induced superconducting gap at much higher temperature ranges. The results that are reproducible and clean suggesting that the hybrid 2D JJs and QICs based on In 0.75 Ga 0.25 As quantum wells could be a promising material platform to realize the real complex and scalable electronic and photonic quantum circuitry and devices.

Large‐Scale On‐Chip Integration of Gate‐Voltage Addressable Hybrid Superconductor–Semiconductor Quantum Wells Field Effect Nano‐Switch Arrays

“…The fabricated junction parameters are commonly shorter than their designed dimensions. [13][14][15][16][17][18][19] A depletion layer will form around the gate electrodes by applying a negative gate voltage to the split gates which defines a constriction in the quantum wells between two superconducting leads. [23,24] The constriction works as an electron waveguide (conducting quantum channel) in such a 2D electron system in our chips.…”

“…Consequently, the hybrid junctions fit into the clean limit regime ( l e > ξ N ) with ballistic transports ( l e >> L ). [ 13 ]…”

“…The hybrid junctions are made from superconducting Nb as their source and drain electrodes and high-quality In 0.75 Ga 0.25 As 2DEG as their active region. [19] The yellow and orange pads and lines in the chip (see Figure 2c) are the two universal gate pads in the chip addressing the junctions and controlling the Cooper-pairs density between the source and drain of each hybrid junction through the application of an external DC voltage across two sides of split gates (yellow for the left, and orange for the right split gate controllers, respectively). Figure 2d is the false-colored SEM image of one gate-voltage controlled field-effect hybrid symmetric and planar 2D junction on the chip.…”

“…[ 4–7 ] Gate‐controlled hybrid electronic devices have recently received considerable interest in quantum technology due to their unique technical advantages, e.g., they can work as conductance or current switches in cryogenic quantum circuits [ 8–10 ] or can be used as an artificial material platform for investigation of Andreev reflection, induced unconventional and topological superconductivity. [ 11–18 ] Such devices can therefore be engineered and integrated with wafer‐scale semiconductor chips to form the building blocks of robust quantum computing systems. For these purposes, i) high yields, such as the reliability of hybrid junction and quantum device fabrication processes, ii) reproducibility of quantum phenomena from junction to junction and chip to chip, and iii) manufacturability of the complex hybrid quantum circuits must be systematically investigated.…”

Visible to Near-infrared Chip-integrated Tunable Optical Modulators Based on Niobium Plasmonic Nano-antenna and Nano-circuit Metasurface Arrays

“…Superconducting-based quantum circuits have demonstrated capability as a primary technology for quantum computing [1][2][3][4][5]. Cryogenic photonic interconnects utilizing optical fibres with their low thermal conductivity have been demonstrated recently to overcome the issue with heat load related to the quantum processors scale up in the dilution refrigerators.…”