Native Two-Qubit Gates in Fixed-Coupling, Fixed-Frequency Transmons Beyond Cross-Resonance Interaction

Fixed-frequency superconducting qubits demonstrate remarkable success as platforms for stable and scalable quantum computing. Cross-

resonance gates have been the workhorse of fixed-coupling, fixed-frequency superconducting processors, leveraging the entanglement generated 

by driving one qubit resonantly with a neighbor’s frequency to achieve high-fidelity, universal controlled-NOT (CNOT) gates. Here, we use on-resonant 

and off-resonant microwave drives to go beyond cross-resonance, realizing natively interesting two-qubit gates that are not equivalent to cnot gates. 

In particular, we implement and benchmark native iswap, swap,  and bswap gates; in fact, any SU(4) unitary can be achieved using these techniques. 

Furthermore, we apply these techniques for an efficient construction of the B gate: a perfect entangler from which any two-qubit gate can be reached 

in only two applications. We show that these native two-qubit gates are better than their counterparts compiled from cross-resonance gates. We 

elucidate the resonance conditions required to drive each two-qubit gate and provide a novel frame tracking technique to implement them in Qiskit.

Fixed-frequency superconducting qubits demonstrate remarkable success as platforms for stable and scalable quantum computing. Cross-resonance 

gates have been the workhorse of fixed-coupling, fixed-frequency superconducting processors, leveraging the entanglement generated by driving one 

qubit resonantly with a neighbor’s frequency to achieve high-fidelity, universal controlled-NOT (CNOT) gates. Here, we use on-resonant and off-

resonant microwave drives to go beyond cross-resonance, realizing natively interesting two-qubit gates that are not equivalent to cnot gates. In 

particular, we implement and benchmark native iswap, swap,  and bswap gates; in fact, any SU(4) unitary can be achieved using these techniques. 

Furthermore, we apply these techniques for an efficient construction of the B gate: a perfect entangler from which any two-qubit gate can be reached 

in only two applications. We show that these native two-qubit gates are better than their counterparts compiled from cross-resonance gates. We 

elucidate the resonance conditions required to drive each two-qubit gate and provide a novel frame tracking technique to implement them in Qiskit.

Article：https://doi.org/10.1103/PRXQuantum.5.020338