Introducing Unimon: A new superconducting qubit for quantum computers

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Superconducting qubits seem promising for useful quantum computers, but the currently widespread qubit designs and techniques do not yet provide high enough performance.

A group of scientists from Aalto University, IQM Quantum Computers, and VTT Technical Research Centre have introduced a new superconducting qubit called Unimon. This Unimon is claimed to increase the accuracy of quantum computations.

The unimon combines the desired characteristics of greater anharmonicity, a complete insensitivity to dc charge noise, decreased sensitivity to magnetic noise, and a simple structure consisting solely of a single Josephson junction in a resonator in a single circuit.

The team achieved fidelities from 99.8% to 99.9% for 13-nanoseconds-long single-qubit gates on three unimon qubits. This is a major milestone in the quest to build commercially useful quantum computers.

Professor Mikko Möttönen, joint Professor of Quantum Technology at Aalto University and VTT, said, “Our aim is to build quantum computers which deliver an advantage in solving real-world problems. Our announcement today is an important milestone for IQM and a significant achievement to build better superconducting quantum computers.”

Eric Hyyppä, who is working on his Ph.D. at IQM, said, “Because of the higher anharmonicity, or non-linearity, than in transmons, we can operate the unimons faster, leading to fewer errors per operation.”

The scientists devised chips with three unimon qubits to experimentally demonstrate the unimon. The niobium was used as superconducting material apart from the Josephson junctions.

The scientists measured the unimon qubit and found it to have noise immunity, only need a single Josephson junction, and have a relatively high anharmonicity. In contrast to the junction-array-based superinductors used in traditional fluxonium or quarton qubits, the geometric inductance of the unimon has the potential to be more predictable and yield-enhancing.

Prof. Möttönen said“Unimons are so simple and have many advantages over transmons. The fact that the first unimon ever made worked this well gives plenty of room for optimization and major breakthroughs. As the next steps, we should optimize the design for even higher noise protection and demonstrate two-qubit gates.”

“We aim for further improvements in the design, materials, and gate time of the unimon to break the 99.99% fidelity target for useful quantum advantage with noisy systems and efficient quantum error correction. This is a very exciting day for quantum computing!”

Journal Reference:

  1. Hyyppä, E., Kundu, S., Chan, C.F. et al. Unimon qubit. Nat Commun 13, 6895 (2022). DOI: 10.1038/s41467-022-34614-w

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