Dissipating quartets of excitations in a superconducting circuit

TL;DR

This paper demonstrates a novel six-wave mixing process in a superconducting circuit that enables targeted dissipation of four-excitation states, advancing quantum error correction techniques for complex bosonic qubits.

Contribution

It introduces a six-wave mixing method using a near Kerr-free Josephson element to selectively dissipate quartets of excitations in a superconducting resonator.

Findings

Achieved order of magnitude increase in decay rate of fourth excited state

Minimal impact on lower energy states' relaxation and coherence

Potential to stabilize complex bosonic qubits like Schrödinger cat states

Abstract

Over the past decade, autonomous stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schr\"odinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended non-linear interactions. In this work, we leverage a genuine six-wave mixing process enabled by a near Kerr-free Josephson element to enforce dissipation of quartets of excitations in a high-impedance superconducting resonator. Owing to residual non-linearities stemming from stray inductances in our circuit, this dissipation channel is only effective when the resonator holds a specific number of photons. Applying it to the fourth excited state of the resonator, we show an order of magnitude enhancement of the state decay rate while only marginally impacting the relaxation and coherence of lower energy states. Given that stray inductances could be strongly reduced through simple modifications in circuit design and that our methods can be adapted to activate even higher-order dissipation channels, these results pave the way toward the dynamical stabilization of four-component Schr\"odinger cat qubits and even more complex bosonic qubits.