Experimental protection of quantum gates against decoherence and control errors

One of the biggest challenges for implementing quantum devices is the requirement to perform accurate quantum gates. The destructive effects of interactions with the environment present some of the most difficult obstacles that must be overcome for precise quantum control. In this work we implement a proof of principle experiment of quantum gates protected against a fluctuating environment and control pulse errors using dynamical decoupling techniques. We show that decoherence can be reduced during the application of quantum gates. High-fidelity quantum gates can be achieved even if the gate time exceeds the free evolution decoherence time by one order of magnitude and for protected operations consisting of up to 330 individual control pulses.

Figure 1

Pulse sequence for protecting quantum gates using the $XY$-4 sequence.

Figure 2

Pulse sequence for a decoherence-protected BB1 pulse using the $XY$-4 sequence.

Figure 3

Process tomography of the Hadamard gate. The panels show the process matrix $\chi$ for an ideal gate and the experimental process matrix of the protected gate.

Figure 4

Gate fidelity as a function of gate time for different gate operations protected by different DD sequences. “Simple” indicates gates that were implemented by unprotected rotations. The delay between the pulses for the noop was $\approx$3 $\mu$s.