Generating families of three-qubit gates from simultaneous two-qubit gates, part 2: experiment

Whether one is working on noisy intermediate-scale quantum (NISQ) algorithms or towards error correction, the coherence of a quantum processor sets bounds on the depth which can be achieved for any sequence of operations. Each of these cases requires the generation of large, entangled states. This is typically achieved by implementing a universal gate set formed of single- and two-qubit operations. While generating these states is achievable, as devices grow larger in terms of the number of qubits, the depth needed to entangle all qubits increases.

In this work, we extend our gate set to include a three-qubit gate which itself can implement a family of operations. This gate is performed by the simultaneous application of two microwave drives between our target states and a shared common level. Driving this lambda-system with equal strength tones generates an effective controlled interaction between the target states which acts as a combination of a CPhase and a SWAP-like gate. For this reason, we call this gate a Controlled-CZ-SWAP or CCZS. We demonstrate the implementation of this gate and benchmark its performance and the arbitrary control of the swapping angle.