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Dissipating Quartets of Excitations in a Superconducting Circuit

A. Vanselow1,2, B. Beauseigneur1,2, L. Lattier1,2, M. Villiers1,2, A. Denis1, P. Morfin1, Z. Leghtas1,2, and P. Campagne-Ibarcq1,2,*

  • *Contact author: philippe.campagne-ibarcq@inria.fr
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Phys. Rev. X 16, 011032 – Published 23 February, 2026

DOI: https://doi.org/10.1103/bjpc-8xcf

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 Schrödinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended nonlinear 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 nonlinearities 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 Schrödinger cat qubits and even more complex bosonic qubits.

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Popular Summary

Qubits encoded in oscillators can be stabilized through tailored interactions with a cold environment. A repetition code of two-legged cat qubits stabilized in this way was recently operated below threshold, demonstrating their potential for hardware-efficient error correction. More advanced bosonic qubits, such as four-legged cat qubits, promise even greater hardware efficiency and error resilience. However, stabilizing these advanced qubits requires higher-order multiphotonic interactions with the environment, posing a significant experimental challenge. In this work, we demonstrate a four-to-one photon exchange between a superconducting resonator and a cold environment, an essential step for stabilizing four-legged cat qubits. While residual nonlinearities in the circuit currently prevent the stabilization of a full-fledged cat state, these effects are well understood and can be mitigated with straightforward circuit design improvements.

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Phys. Rev. X 16, 011032– Published 23 February, 2026
  • Received 14 January 2025
  • Accepted 10 December 2025
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