Alice & Bob has demonstrated a new method for stabilizing cat qubits using a direct current voltage bias of approximately one microvolt, potentially simplifying the construction of future quantum computers, the company says. The Paris and Boston-based company achieved a two-photon exchange rate of 3 MHz with the new coupler, exceeding the performance of previously pumped designs and opening the door to more complex qubit operations. This approach allows for control over photon exchange, switching between one, two, or four photons, with a bias of 1.1 microvolts, a feat previously difficult to achieve.
DC Voltage Bias Stabilizes Cat Qubits via Tunable Photon Exchange
This new method relies on a SQUID, a superconducting quantum interference device, biased with a DC voltage to facilitate photon exchange between a memory resonator and a buffer resonator. The team directly observed photons dissipating in pairs using Wigner tomography, confirming the intended stabilization process. Changing only the voltage switched the device between exchanging photons one, two, or four at a time, a two-photon process occurring at a bias of about 1.1 microvolts.
This level of control is critical for exploring more complex cat qubit encodings, specifically four-component cat qubits which encode information across four coherent states, a configuration previously difficult to achieve. Four-to-one photon processes are very difficult to achieve with sufficient strength, but DC-biasing junctions seems to be a viable approach to that goal, explained Benjamin Huard, Scientific Advisor and Professor at Ecole Normale Supérieure de Lyon.
The technique also suppresses an unwanted frequency shift that typically accompanies cat qubit stabilization, a parasitic effect that can degrade performance. The research, conducted in collaboration with the École Normale Supérieure de Lyon, expands the toolbox for cat qubit development, offering an alternative to microwave-driven stabilization.
Participation in Europe’s first quantum error correction network, alongside contributions to QuBriC, a doctoral network focused on quantum error correction, emphasises their broader commitment to advancing the field, according to Alice & Bob. The findings, published as a preprint in August 2026, detail how a Cooper pair tunneling across the SQUID, driven by the DC bias, enables the energetically favorable exchange of photons between the memory and buffer resonators.
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