Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas (1711.07665v3)

Abstract: The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting circuits, from setting qubit transition frequencies and interqubit coupling strengths, to the gain of parametric amplifiers for quantum-limited readout. The inductance is either set by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices (SQUIDs) with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant which employs locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control. Here, we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show 2DEG gatemons meet the requirements by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 us, limited by dielectric loss in the 2DEG host substrate.

Superconducting Gatemon Qubit Based on a Proximitized Two-Dimensional Electron Gas

The paper presents an experimental realization of a superconducting gatemon qubit architecture utilizing a proximitized two-dimensional electron gas (2DEG) as a platform. This work evaluates the viability of 2DEG-based gatemons for scalable quantum computing, addressing key metrics of suitability, including qubit coherence, tunability, and operational fidelity.

The researchers explore a novel implementation where gatemons, a transmon qubit variant, are built using a two-dimensional electron gas with superconducting elements forming the Josephson junction (JJ). Unlike traditional JJ implementations using metal-oxide layers, this approach leverages semiconductor-superconductor hybrids, presenting an all-electric tunability through local gate-voltage control which negates the need for high-power magnetic fields and mitigates issues related to flux noise. The superconducting-semiconductor interface is established with an in-situ epitaxial layer of aluminum on an InAs 2DEG, achieving high transparency and optimal superconducting characteristics.

Key numerical outcomes of the paper validate this concept. Single qubit coherence times are reported up to 2 $\mu$s, with qubit energies and coupling strengths stable over variations in qubit structure dimensions. Using all-electric control methods, the experiments demonstrated single qubit operations, as well as two-qubit operations involving coherent excitation swapping between paired qubits. The tuning of qubit frequencies reached a tunable range of $\sim$1 GHz/V, a significant margin that accommodates robust control in multi-qubit systems.

An examination of the qubit relaxation and dephasing times indicates that the performance is currently bounded by dielectric losses rather than limitations inherent in the 2DEG or its interface quality. The relaxation time T$_1$ varied from 0.2 - 2 $\mu$s, and coherence was shown to be affected by dielectric properties suggesting future enhancements through substrate and material-shell optimizations.

From a theoretical and design perspective, this research bridges scalable integration of quantum circuits with semiconductor technologies. It suggests that planar semiconductor and superconducting materials combined into hybrid platforms could leverage advanced microelectronic fabrication techniques. The research presented stands as an invitation for further exploration into quantum processor designs that align better with existing semiconductor processing capabilities.

Future research avenues might focus on material enhancements for suppression of dielectric losses, integration strategies for future quantum processors, and further studies on qubit fidelity amid scaling the number of interacting qubits. Also, deeper investigations into the context of noisy intermediate-scale quantum (NISQ) devices could build theoretical constructs around hybrid architectures, contributing both to near-term and long-term quantum computation goals.

By presenting a viable alternative to traditional superconducting qubit implementations, this research enriches the toolkit available for developing quantum hardware, offering a pathway that balances coherence, tunability, and integration potential with the demands of next-generation quantum information processing platforms.