A peer-reviewed experiment reshaped control pulses to reduce unwanted transitions in a single superconducting qubit. Pulses lasting 6.8 nanoseconds achieved fidelity above 99.98 per cent while suppressing leakage beyond the two computing states. The method addresses transitions that simpler corrections overlook; testing involved an isolated device, with performance in coupled processors still to be demonstrated.
A single peer-reviewed experiment controlled an isolated transmon, a superconducting circuit used as a quantum bit. Its 6.8-nanosecond pulses performed X and half-X rotations with fidelity above 99.98 per cent. These operations change the qubit's state. The experiment targets the loss of population into energy levels outside the two used for computation; extra padding around a pulse means its duration is distinct from a whole processor cycle.[1]
A transmon has more than two accessible energy levels. Strong pulses can drive transitions between levels that are not neighbours, through multiphoton processes. The new correction reshapes the pulse to suppress those pathways as well as the more familiar unwanted transitions. The team combined randomized benchmarking with a sequence that amplifies coherent leakage through repeated operations, making very small leakage effects easier to measure.[1]
Leakage increased again when the pulses became shorter still, and calibration grew less stable. Near the best operating point, much of the residual error involved the loss of quantum coherence. The amplified measurement also responds differently to thermal leakage. These results concern a single isolated qubit; coupled devices, simultaneous operations and processor interference remain further experimental conditions for the method.[1]
