High-fidelity gate operations for quantum computing beyond dephasing time limits

The implementation of quantum gates with fidelities that exceed the threshold for reliable quantum computing requires robust gates whose performance is not limited by the precision of the available control fields. The performance of these gates also should not be affected by the noisy environment of the quantum register. Here we use randomized benchmarking of quantum gate operations to compare the performance of different families of gates that compensate errors in the control field amplitudes and decouple the system from the environmental noise. We obtain average fidelities of up to 99.8%, which exceeds the threshold value for some quantum error correction schemes as well as the expected limit from the dephasing induced by the environment.

Figure 1

Sequences of gate operations compared in this work. The double arrows indicate the gate duration $\tau$, defined as the time period between the beginning of one $P$ gate to the beginning of the next $P$ gate.

Figure 2

Experimental survival probabilities averaged over 32 sequences for BB1 gates as a function of the number of gates. The solid lines represent an exponential fit and theoretical predictions (see text).

Figure 3

Experimental results for different types of gates.

Figure 4

Decay of the survival probability measured by interleaving quantum gates with the dynamical decoupling XY-4 and pure dynamical decoupling.