Experimental Realization of Rabi-Driven Reset for Fast Cooling of a High-Q Cavity

Abstract

High-Q bosonic memories are central to hardware-efficient quantum error correction, but their isolation makes fast, high-fidelity reset a persistent bottleneck. Existing approaches either rely on weak intermode cross-Kerr conversion or on measurement-based sequences with substantial latency. Here we demonstrate a hardware-efficient Rabi-Driven Reset (RDR) that implements continuous, measurement-free cooling of a superconducting cavity mode. A strong resonant Rabi drive on a transmon, together with sideband drives on the memory and readout modes detuned by the Rabi frequency, converts the dispersive interaction into an effective Jaynes-Cummings coupling between the qubit dressed states and each mode. This realizes a tunable dissipation channel from the memory to the cold readout bath. Crucially, the engineered coupling scales with the qubit-mode dispersive interaction and the drive amplitude, rather than with the intermode cross-Kerr, enabling fast cooling even in very weakly coupled architectures that deliberately suppress direct mode-mode coupling. We demonstrate RDR of a single photon with a decay time of $1.2 μs$, more than two orders of magnitude faster than the intrinsic lifetime. Furthermore, we reset about 30 thermal photons in about $80 μs$ to a steady-state average photon number of $\bar{n} = 0.045 \pm 0.025$.

Figures (6)

• Figure 1: Experiment scheme. (a) A cross-sectional view of a high-Q flute cavity fluteCavity2021, where the TE102 mode is dispersively coupled to a transmon qubit, which in turn is coupled to a stripline readout resonator. The sideband drives for each mode and the Rabi drive are applied through designated ports (For the full wiring diagram see Appendix \ref{['appendix:system']}.). The cavity includes room for an additional qubit, left vacant in this experiment. (b) Illustration of the sideband cooling mechanism. The orange arrow indicates sideband coupling between the memory mode and the Rabi-driven qubit’s dressed states. The undulating line denotes qubit decay through the readout mode. (c) Wigner functions of a thermal state actively cooling down in frame displaced by $-\bar{a}_me^{\mathrm{i}\Omega_Rt}$.
• Figure 2: Reset of a thermal state. (a) Pulse sequence for reset and measurement of arbitrary coherent or incoherent states. Solid (dashed) lines correspond to the real (imaginary) parts of the pulses. The $M1$ measurement (applied using an intrinsic readout mode reset pulse shape drachma) is used to post-select the state of the qubit, as in Ref. ECD and $M2$ is the actual characteristic function measurement. (b) Wigner characteristic function averaged over the real and imaginary axes of $\alpha$. Different times are vertically shifted for clarity. The fit considered only points above a threshold between 0.7 and 0.85. (c) Average photon number as a function of time for active reset compared to the natural decay of the memory mode. The shaded regions signify uncertainty about $\bar{n}$ due to fitting of different number of data points with respect to different thresholds. The active reset data is fitted to a piecewise linear-exponential function (Eq. \ref{['eq:nbar_vs_t']}), and the natural decay data is fitted to an exponential function.
• Figure 3: Reset of a single Fock state by RDR. (a) The measured Wigner characteristic functions of the memory mode during the reset process. The initial single Fock state was generated with fidelity of $80\%$ and was cooled down to a vacuum state with fidelity of $93\%$. (b) Vacuum Rabi oscillations between the dressed qubit and the displaced memory mode. (c) Probability of the memory mode being in the vacuum state, extracted using maximum likelihood estimation of the Wigner characteristic functions. The probability is fitted to an exponential decay.
• Figure 4: Full experimental system schematics.
• Figure 5: Stark-shift measurements as a function of drive.