ISTA fluxonium design switches bit-flip protection on demand with 10 ns gates

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Researchers at the Institute of Science and Technology Austria have proposed a clever new design for fluxonium superconducting qubits. Quantum Zeitgeist covered the paper by C. A. Siegele, A. A. Sokolova, L. N. Kapoor, F. Hassani and J. M. Fink. The key idea is a qubit whose protection against bit flip errors can be turned up or down in real time

That solves a long standing dilemma. Heavily protected qubits are great at storing information, but they are hard to control quickly, because the same protection makes them resistant to the signals used to manipulate them. Lightly protected qubits are easy to control but lose information faster. This design lets one qubit switch between the two modes

In the heavy setting, the qubit's energy relaxation time could in principle reach hours. In the light setting, it can be controlled quickly. The difference in relaxation times between the two modes is roughly 100,000 to 1,000,000 times. The switch works by using magnetic flux to tune either the Josephson energy or the charging energy, or in a second version by switching in a large capacitance

The gates are remarkably fast. Single and two qubit gates use flux pulses of about 10 nanoseconds, a speed that usually requires microwave control. A simulated single qubit gate reached an infidelity of 2 x 10^-5 with a 7.5 nanosecond pulse. The team expects dephasing, rather than relaxation, to be the main limit

These are simulation results rather than a hardware demonstration, so the next step is building the device. If it works as predicted, protection on demand could be a very useful tool for superconducting quantum computers, combining long memory with fast processing in the same qubit

Could switchable protection become standard in superconducting qubit design? And how much do you trust simulated gate fidelities before hardware results?

Superconducting Qubits Now Switch States In Just 10 Nanosecondsquantumzeitgeist.com