Parity Cross-Resonance: A Multiqubit Gate
This work addresses the need for more efficient multiqubit operations in superconducting quantum processors, representing an incremental advance in gate design.
The researchers developed a native three-qubit entangling gate that enables control-control-target and control-target-target operations in a single step, which they demonstrated can be used for GHZ state preparation, Toffoli-class logic, and implementing controlled-ZZ gates for faster, higher-fidelity stabilizer measurements in surface-code quantum error correction.
We present a native three-qubit entangling gate that exploits engineered interactions to realize control-control-target and control-target-target operations in a single coherent step. Unlike conventional decompositions into multiple two-qubit gates, our hybrid optimization approach selectively amplifies desired interactions while suppressing unwanted couplings, yielding robust performance across the computational subspace and beyond. The new gate can be classified as a cross-resonance gate. We show it can be utilized in several ways, for example, in GHZ triplet state preparation, Toffoli-class logic demonstrations with many-body interactions, and in implementing a controlled-ZZ gate. The latter maps the parity of two data qubits directly onto a measurement qubit, enabling faster and higher-fidelity stabilizer measurements in surface-code quantum error correction. In all these examples, we show that the three-qubit gate performance remains robust across Hilbert space sizes, as confirmed by testing under increasing total excitation numbers. This work lays the foundation for co-designing circuit architectures and control protocols that leverage native multiqubit interactions as core elements of next-generation superconducting quantum processors.