Fast qubit resetting with a quantum-circuit refrigerator*

Superconducting qubits have emerged as powerful building blocks for a quantum computer. However, precise reset of qubits into their ground states remains a challenge. Although qubits naturally relax, this process is slow for high-coherence qubits and eventually inhibits fast computing. A way forward is provided by a voltage-tunable quantum-circuit refrigerator (QCR), a microcooler based on photon-assisted electron tunneling in a pair of NIS junctions. Here, we present an experimental realization of a QCR coupled to a transmon qubit as well as its optimization for fast on-demand qubit reset.

We evaluate the influence of a QCR on characteristic qubit lifetimes T₁ and T₂ and present a coupling design that allows for both long qubit lifetime and efficient cooling. Furthermore, we show the effects of pulsed operation of the QCR, which enables a reset of the qubit state in the nanosecond range, considering various noise levels. This device not only improves qubit performance, but offers a versatile platform for studies on open quantum systems.