Scalable native multiqubit gates via engineered noncomputational-state interactions in superconducting fluxonium qubits

TL;DR

This paper presents a scalable method for implementing native multi-controlled multiqubit gates in superconducting fluxonium qubits, reducing circuit complexity and error rates for future quantum computing applications.

Contribution

The authors introduce a novel protocol leveraging engineered noncomputational state interactions to realize multi-controlled gates supporting arbitrary control qubits in fluxonium qubits.

Findings

Achieved $CCZ$, $CCCZ$, and $CCCCZ$ gates with errors around 0.01 to 0.001.

Gate lengths range from 50 ns to 300 ns depending on the gate complexity.

Compatible with existing single- and two-qubit gate implementations.

Abstract

Native multiqubit gates could be essential for bridging the gap from current noisy devices to future utility-scale quantum computers, as they can substantially reduce circuit depth for near-term applications on noisy devices and may also lower the physical overhead of fault-tolerant quantum computation. Here we introduce a scalable protocol for implementing native multi-controlled gates on fluxonium qubits, supporting an arbitrary number of control qubits ($N > 1$) while remaining compatible with existing single- and two-qubit gate realizations. Our approach leverages engineered interactions in noncomputational state manifolds to enable qubit-state selective transitions, which is activated for the direct implementation of $(C^{\otimes N})Z$ gates. We show that in square lattices with fluxonium qubits, $CCZ$, $CCCZ$, and $CCCCZ$ gates with errors around 0.01 (0.001) are achievable, with gate lengths of $50\,(100)\,\text{ns}$, $100\,(250)\,\text{ns}$, and $150\,(300)\,\text{ns}$, respectively. Looking forward, integrating these native multi-controlled gates with primitive single- and two-qubit gate sets within a single quantum processor could significantly enhance flexibility in circuit synthesis and offer a promising alternative pathway toward utility-scale quantum computing.