Tunable Interactions for Implementing Two-Qubit Gates and Suppressing Spurious Couplings Via Off-Resonantly Driven Coupler Modes in a Superconducting Chip

Technology

This invention consists of a novel method to enhance or suppress multiqubit interactions by applying off-resonant microwave drives to coupler modes that connect the qubits. Enclosed methods exploit the yet unreported phenomenon that in the presence of an off-resonant microwave drive on a coupler node, the “ZZ” interaction strength between two qubits can be made arbitrarily large at particular drive frequencies. Additionally, several poles in the ZZ interaction strength appear in relatively narrow frequency bands which may be engineered to not overlap with the resonant transitions of the proposed two-qubit + coupler system. This allows for large ZZ interaction rates that are stable in drive power and frequency, useful for implementing a controlled-Z or CZ gate.  

Problem Addressed

This technology offers hardware-efficient methods to address qubits for high-fidelity gates while also being able to easily decouple systems when idling. Compared to existing coupler-mediated gates, this technology does not require fast-flux lines to be installed on a chip, a process which can be inconvenient for scaling a system to accommodate many qubits. Qubits can thus be accommodated in a relatively large frequency band, alleviating issues related to frequency crowding and allowing qubit operation at a more optimal frequency.  

Advantages

• Reduces frequency crowding and spurious interactions between qubits 

• Substantial gains in gate fidelities 

• Suppresses propagation of correlated errors