Kerr-cat qubits realized in periodically driven superconducting nonlinear resonators are a promising platform for quantum information processing with biased noise. Pure dephasing insuch systems induces leakage out of the qubit subspace, motivating the use of quantum circuit refrigeration (QCR) to remove excess excitations. While conventional superconductor–insulator–normal-metal–insulator–superconductor (SINIS)-based QCRs can suppress leakage via single-photon absorption, they also enhance QCR-induced phase-flip errors. Here we investigate a QCR based on a superconductor–insulator–superconductor–insulator–superconductor (SISIS) junction coupled to a Kerr parametric oscillator (KPO). We show that a SISIS-based QCR can operate in a regime where single-photon processes are suppressed while two-photon absorption dominates. As a result, the proposed SISIS-based QCR achieves strong suppression of dephasing-induced leakage while substantially reducing the increase in phase-flip errors associated with QCR operation. These results demonstrate that the proposed SISIS-based QCR provides an effective approach for mitigating leakage while limiting QCR-induced phase-flip errors in Kerr-cat qubits.
We experimentally studied the switching off processes in the double-resonator coupler superconducting quantum this http URL both frequency and time-domain, we observed the variationof qubit-qubit effective coupling by tuning qubits’frequencies. According to the measurement results, by just shifting qubits‘ frequencies smaller than 50 MHz, the effective qubit-qubit coupling strength can be tuned from switching off point to two qubit gate point (effective coupling larger than 5 MHz) in double-resonator superconducting quantum circuit. The double-resonator coupler superconducting quantum circuit has the advantage of simple fabrications, introducing less flux noises, reducing occupancy of dilution refrigerator cables, which might supply a promising platform for future large-scale superconducting quantum processors.
Engineering quantum tunnelling in phase space has emerged as a viable method for creating a protected qubit with biased-noise properties. A promising approach is to combine a Kerr nonlinearitywith multi-photon transitions, resulting in a system known as a Kerr parametric oscillator (KPO). In this work, we implement a three-photon KPO and explore its potential as a protected qutrit. We confirm quantum coherence by demonstrating three-photon Rabi oscillations and performing direct Wigner function measurements that reveal three-component cat-like states. We observe breathing-like dynamics in phase space, arising from exotic temporal interference between the qutrit and excited states. The frequency of this interference corresponds to the energy gap between the qutrit and excited manifolds, thereby providing an experimental hallmark of qutrit space protection. We also identify a higher-order pump term as the main mechanism suppressing photon occupation; mitigating this term is necessary to maximize protection. Our findings elucidate the basic quantum properties of the three-photon KPO and establish the first step toward its use as an alternative qutrit platform.