High-Coherence and High-frequency Quantum Computing: The Design of a High-Frequency, High-Coherence and Scalable Quantum Computing Architecture

Abstract

High-coherence, fault-tolerant and scalable quantum computing architectures with unprecedented long coherence times, faster gates, low losses and low bit-flip errors may be one of the only ways forward to achieve the true quantum advantage. In this context, high-frequency high-coherence (HCQC) qubits with new high-performance topologies could be a significant step towards efficient and high-fidelity quantum computing by facilitating compact size, higher scalability and higher than conventional operating temperatures. Although transmon type qubits are designed and manufactured routinely in the range of a few Giga-Hertz, normally from 4 to 6 GHz (and, at times, up to around 10GHz), achieving higher-frequency operation has challenges and entails special design and manufacturing considerations. This report presents the proposal and preliminary design of an 8-qubit transmon (with possible upgrade to up to 72 qubits on a chip) architecture working beyond an operation frequency of 10GHz, as well as presents a new connection topology. The current design spans a range of around 11 to 13.5 GHz (with a possible full range of 9-12GHz at the moment), with a central optimal operating frequency of 12.0 GHz, with the aim to possibly achieve a stable, compact and low-charge-noise operation, as lowest as possible as per the existing fabrication techniques. The aim is to achieve average relaxation times of up to 1.9ms with average quality factors of up to 2.75 x 10^7 after trials, while exploiting the new advances in superconducting junction manufacturing using tantalum and niobium/aluminum/aluminum oxide tri-layer structures on high-resistivity silicon substrates (carried out elsewhere by other groups and referred in this report).