Breaking the trade-off between fast control and long lifetime of a superconducting qubit

S Kono,D Lachance-Quirion,A F Van Loo,A Noguchi,K Koshino,Y Tabuchi,Y Nakamura

doi:10.1038/s41467-020-17511-y

Abstract

The rapid development in designs and fabrication techniques of superconducting qubits has made coherence times of qubits longer. In the future, however, the radiative decay of a qubit into its control line will be a fundamental limitation, imposing a trade-off between fast control and long lifetime of the qubit. Here, we break this trade-off by strongly coupling another superconducting qubit along the control line. This second qubit, which we call “Josephson quantum filter” (JQF), prevents the first qubit from emitting microwave photons and thus suppresses its relaxation, while transmitting large-amplitude control microwave pulses due to the saturation of the quantum filter, enabling fast qubit control. This device functions as an automatic decoupler between a qubit and its control line and could help in the realization of a large-scale superconducting quantum processor by reducing the heating of the qubit environment and the crosstalk between qubits.

Highlights

The rapid development in designs and fabrication techniques of superconducting qubits has made coherence times of qubits longer
This is a fundamental trade-off between fast control and long lifetime of a qubit, which originates from the fluctuation–dissipation theorem[5]
The radiative decay of a superconducting qubit to its control line can no longer be dismissed in devices with state-of-the-art coherence times

Summary

Introduction

The rapid development in designs and fabrication techniques of superconducting qubits has made coherence times of qubits longer. We break this trade-off by strongly coupling another superconducting qubit along the control line This second qubit, which we call “Josephson quantum filter” (JQF), prevents the first qubit from emitting microwave photons and suppresses its relaxation, while transmitting large-amplitude control microwave pulses due to the saturation of the quantum filter, enabling fast qubit control. This device functions as an automatic decoupler between a qubit and its control line and could help in the realization of a large-scale superconducting quantum processor by reducing the heating of the qubit environment and the crosstalk between qubits. A larger coupling strength to the control degree of freedom achieves a faster gate operation for a given drive amplitude, it increases the radiative decay of the qubit into the continuous mode. The Purcell filter circuit is not suitable, for a case where the frequencies of the radiative decay and the control signal are identical

Methods

Results

Conclusion