The challenge of rapidly and reliably resetting quantum memories represents a significant obstacle to building practical quantum computers.

Eliya Blumenthal, Natan Karaev, and Shay Hacohen‑Gourgy, all from the Technion – Israel Institute of Technology, have demonstrated a novel technique to address this issue, achieving substantially faster cooling of a high‑quality cavity. Their research details a hardware‑efficient Rabi‑Driven Reset (RDR) method that continuously cools a cavity mode without requiring measurement, overcoming limitations of existing approaches that rely on weak interactions or lengthy measurement sequences. By engineering an effective coupling between the cavity and a cold readout bath, the team achieved a photon‑decay time orders of magnitude faster than the cavity’s natural lifetime. This breakthrough paves the way for improved performance in quantum error‑correction schemes and represents a crucial step toward scalable quantum technologies.

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Rabi‑Driven Reset for Fast Quantum Memory Cooling

High‑Q bosonic memories are essential for building hardware‑efficient quantum‑error‑correction systems, yet their inherent isolation presents a significant challenge: fast, high‑fidelity reset. Current methods rely on either weak inter‑mode coupling or measurement‑based sequences that introduce substantial delays. Scientists have now demonstrated a hardware‑efficient Rabi‑Driven Reset (RDR) technique, achieving continuous, measurement‑free cooling of a superconducting cavity mode. This innovative approach employs a strong resonant Rabi drive on a transmon, combined with sideband drives on both the memory and readout modes, detuned by the Rabi frequency, to transform the dispersive interaction into an effective Jaynes‑Cummings coupling between the qubit’s dressed states and each mode.

The team engineered a tunable dissipation channel that directs energy from the memory mode to a cold readout bath. Crucially, the engineered coupling scales with the dispersive interaction to the qubit and the drive amplitude, rather than relying on the inter‑mode cross‑Kerr effect, allowing rapid cooling even in architectures designed to minimise direct mode‑mode coupling. Experiments revealed that RDR can decay a single photon in 1.2 µs, exceeding the performance of existing methods by more than two orders of magnitude compared with the intrinsic lifetime of the system. The research also demonstrated the ability to reset approximately 30 thermal photons in 80 µs, reducing the average photon number to a steady‑state value of 0.045 ± 0.025.

The breakthrough extends a cooling protocol originally developed for qubits, applying a strong Rabi drive alongside sideband drives to induce an effective Jaynes‑Cummings interaction. By operating in a displaced frame, the scientists established a Hamiltonian that facilitates efficient energy dissipation from the memory mode to the readout mode, ultimately achieving rapid and continuous cooling. The core innovation lies in the scaling of the coupling rate, which depends on the dispersive coupling to the qubit and the drive amplitude, circumventing the limitations of methods reliant on the cross‑Kerr coupling. This allows for faster cooling rates, particularly in weakly coupled systems.

The experimental setup involved a high‑Q cavity, dispersively coupled to a transmon qubit, which is in turn coupled to a stripline readout resonator, enabling precise control and measurement of the cooling process. This work opens new avenues for developing practical and efficient quantum‑error‑correction schemes by addressing the critical bottleneck of fast, high‑fidelity reset in bosonic quantum systems.

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Rabi‑Driven Reset for Continuous Bosonic Cooling

The research addresses a critical challenge in quantum error correction: the slow reset speed of high‑Q bosonic memories. Scientists developed a novel technique, Rabi‑Driven Reset (RDR), to achieve continuous, measurement‑free cooling of a cavity mode, circumventing limitations of existing methods that rely on weak inter‑mode coupling or lengthy measurement sequences. This approach harnesses a strong resonant Rabi drive applied to a transmon qubit, alongside sideband drives on both the memory and readout modes, all detuned by the Rabi frequency. The core of RDR lies in converting the dispersive interaction between the qubit and cavity modes into an effective Jaynes‑Cummings coupling between dressed states.

The engineered coupling scales with the dispersive interaction and drive amplitude, rather than the typically limiting inter‑mode cross‑Kerr, allowing rapid cooling even in weakly coupled systems. Experiments employed a high‑Q electromagnetic mode resonating at 6.914 GHz with a single‑photon lifetime of 170 µs, dispersively coupled to a transmon qubit with a strength of 57 kHz. The qubit, with a transition frequency of 6.33 GHz and anharmonicity of 265 MHz, is also coupled to a readout resonator at 7.7 GHz, possessing a linewidth of 0.382 MHz and a dispersive shift of 0.635 MHz. To implement RDR, the team calibrated drive amplitudes, selecting a Rabi frequency of 9 MHz, exceeding all other system parameters.

Drive‑induced Stark shifts were meticulously measured using Ramsey experiments to fine‑tune the drive powers, ensuring optimal coupling. The resulting effective Hamiltonian facilitates a tunable dissipation channel, directing energy from the memory mode to a cold readout bath. This method achieved a decay time for a single‑photon reset representing an improvement of over two orders of magnitude compared with the intrinsic lifetime. Furthermore, the study demonstrated the ability to reset approximately 30 thermal photons in around 80 µs, achieving a steady‑state average photon number of 0.045, showcasing the efficiency and scalability of the RDR technique.

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Rabi‑Driven Reset Achieves Photon‑Cooling Breakthrough

Scientists achieved a breakthrough in quantum error correction with the demonstration of a hardware‑efficient Rabi‑Driven Reset (RDR) technique, enabling continuous, measurement‑free cooling of a cavity mode. The work details a method for rapidly resetting quantum memories, a persistent challenge in building scalable quantum computers. Experiments revealed that RDR cools a single photon with a decay time of 1.2 µs, exceeding previous methods by more than two orders of magnitude. This substantial improvement stems from an engineered coupling mechanism that scales with dispersive interactions and drive amplitude, rather than relying on direct mode‑mode coupling.

The team implemented RDR on an electromagnetic mode with a frequency of 6.914 GHz, dispersively coupled to a transmon qubit with a strength of 57 kHz. Characterisation of the transmon revealed a first transition frequency of 6.33 GHz, an anharmonicity of 265 MHz, a relaxation time of 25 µs, and an echoed dephasing time of 20 µs. The readout mode, resonant at 7.7 GHz, exhibited a linewidth of 0.382 MHz and a dispersive shift of 0.635 MHz. Calibration of the drives, including a resonant Rabi drive of 9 MHz, was crucial for establishing the optimal cooling parameters. Results demonstrate the ability to reset approximately 30 thermal photons in about 800 ns to a steady‑state average photon number of 0.045, as determined through Wigner‑characteristic‑function measurements.

Data show that the photon decay rate is bounded by the cavity linewidth, exhibiting a linear decay at high photon numbers and an exponential decay at low photon numbers. Fitting a piecewise linear‑exponential function to the data, scientists recorded a maximum decay rate of ‑0.73 MHz for optimal coupling, significantly faster than the natural decay of the memory mode. Further experiments involved preparing and cooling a single Fock state, achieved through a modified Jaynes‑Cummings interaction. By applying drives for a duration of π/(2χₘ), the team successfully created a single photon in the memory mode, demonstrating a potential pathway for generating higher Fock states rapidly. Measurements confirm that the cooling rate is limited by the readout mode linewidth, with a maximum observed rate of approximately κ/3.3, paving the way for further optimisation and advancements in quantum‑memory technology.

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Reference

Experimental Realization of Rabi‑Driven Reset for Fast Cooling of a High‑Q Cavity – arXiv: 2601.10385 [quant‑ph] (https://arxiv.org/abs/2601.10385)