High-fidelity three-qubit iToffoli gate for fixed-frequency superconducting qubits

Kavli Affiliate: Irfan Siddiqi

| First 5 Authors: Yosep Kim, Alexis Morvan, Long B. Nguyen, Ravi K. Naik, Christian Jünger

| Summary:

The development of noisy intermediate-scale quantum (NISQ) devices has
extended the scope of executable quantum circuits with high-fidelity single-
and two-qubit gates. Equipping NISQ devices with three-qubit gates will enable
the realization of more complex quantum algorithms and efficient quantum error
correction protocols with reduced circuit depth. Several three-qubit gates have
been implemented for superconducting qubits, but their use in gate synthesis
has been limited due to their low fidelity. Here, using fixed-frequency
superconducting qubits, we demonstrate a high-fidelity iToffoli gate based on
two-qubit interactions, the so-called cross-resonance effect. As with the
Toffoli gate, this three-qubit gate can be used to perform universal quantum
computation. The iToffoli gate is implemented by simultaneously applying
microwave pulses to a linear chain of three qubits, revealing a process
fidelity as high as 98.26(2)%. Moreover, we numerically show that our gate
scheme can produce additional three-qubit gates which provide more efficient
gate synthesis than the Toffoli and iToffoli gates. Our work not only brings a
high-fidelity iToffoli gate to current superconducting quantum processors but
also opens a pathway for developing multi-qubit gates based on two-qubit
interactions.

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