Coupler-Assisted Controlled-Phase Gate with Enhanced Adiabaticity

TL;DR

This paper provides a theoretical analysis of a scalable controlled-phase gate in superconducting qubits, explaining its high fidelity mechanism and proposing optimized adiabatic pulse shaping to improve quantum gate performance.

Contribution

It offers a detailed understanding of the high-contrast ZZ interaction and introduces a method for optimizing adiabatic pulses in multilevel systems for quantum gates.

Findings

Explains the origin of high-contrast ZZ interaction.

Develops a method for shaping adiabatic pulses.

Predicts potential two-qubit gate error rate near 10^-5.

Abstract

High-fidelity two-qubit entangling gates are essential building blocks for fault-tolerant quantum computers. Over the past decade, tremendous efforts have been made to develop scalable high-fidelity two-qubit gates with superconducting quantum circuits. Recently, an easy-to-scale controlled-phase gate scheme that utilizes the tunable-coupling architecture with fixed-frequency qubits [Phys. Rev. Lett. 125, 240502; Phys. Rev. Lett. 125, 240503] has been demonstrated with high fidelity and attracted broad interest. However, in-depth understanding of the underlying mechanism is still missing, preventing us from fully exploiting its potential. Here we present a comprehensive theoretical study, explaining the origin of the high-contrast ZZ interaction. Based on improved understanding, we develop a general yet convenient method for shaping an adiabatic pulse in a multilevel system, and identify how to optimize the gate performance from design. Given state-of-the-art coherence properties, we expect the scheme to potentially achieve a two-qubit gate error rate near $10^{-5}$, which would drastically speed up the progress towards fault-tolerant quantum computation.