Alice & Bob tests dc voltage bias for faster cat qubit stabilization

Alice & Bob and École Normale Supérieure de Lyon reported a new way to stabilize cat qubits using a steady dc voltage instead of a microwave pump. The approach could simplify quantum hardware, reduce heat, and open the door to higher-order cat-qubit designs.

Why it matters: - The new biasing method could make cat-qubit hardware more compact, easier to wire and cooler to run inside quantum refrigerators. - The approach could help future quantum computers scale with less complexity than microwave-driven designs. - The same device can support higher-order photon processes, including four-photon interactions that are difficult to realize with existing methods.

What happened: - Alice & Bob and École Normale Supérieure de Lyon announced a new cat-qubit stabilization method in superconducting quantum systems. - The researchers used a steady voltage of about one millionth of a volt instead of a microwave drive. - The work was carried out at ENS Lyon in collaboration with Alice & Bob. - The findings were published in a preprint in August 2026.

The details: - Cat qubits store information in a microwave resonator. - Stabilization works by dissipating photons from the resonator into the environment in pairs. - In the new setup, the coupler is biased with dc voltage through a SQUID. - A Cooper pair tunneling across the SQUID exchanges an energy of 2eV with the circuit. - The bias is chosen so 2eV matches the energy difference between two memory photons and one buffer photon. - The tunneling event converts two memory photons into one buffer photon that quickly leaks away. - The device produced effective two-photon dissipation at a rate of up to 1.3 MHz. - The team measured a two-photon exchange rate of 3 MHz. - The data suggests the design could reach considerably higher rates. - Changing only the voltage switched the device between one-photon, two-photon and four-photon exchange modes. - The researchers directly imaged the memory state with Wigner tomography and observed photons leaving in pairs. - The new strategy suppresses the unwanted change of frequency with photon number that can harm cat codes.

Between the lines: - The result is not a replacement for existing cat-qubit control methods. It expands the toolset. - DC-biasing junctions may offer a practical path to four-component cat qubits, which encode information across four coherent states. - Benjamin Huard, scientific advisor at Alice & Bob and professor at ENS Lyon, said four-to-one photon processes are difficult to achieve with sufficient strength and that dc-biasing junctions appear viable for that goal. - Voltage lines are compact, straightforward to wire and generate little heat, which is attractive for scaling quantum systems. - Alice & Bob has long focused on cat qubits, so the result fits the company’s broader hardware strategy.

What’s next: - The next step is to test whether the dc-bias approach can deliver even higher exchange rates and more robust multi-photon operations. - Researchers will likely explore whether the method can support practical four-component cat-qubit architectures. - Further integration work will determine how well the approach fits larger-scale quantum computer designs.

The bottom line: - A tiny dc voltage may offer a simpler, cooler way to stabilize cat qubits and expand the range of quantum operations available on chip.