Multiqubit entanging gates for superconducting qubit systems

Superconducting qubits are a leading platform for quantum computing, offering substantial flexibility in designing qubits and gate operations. The standard approach relies on repeatedly applying single- and two-qubit gates to construct arbitrary quantum circuits. We propose an alternative strategy that leverages multiqubit entangling gates between superconducting qubits by simultaneously turning on multiple qubit-qubit interactions. In particular, we derive analytical forms of three-qubit gates in a transmon system and demonstrate their application in test circuits that generate entangled states such as GHZ and W states, as well as to implement standard three-qubit logic gates, including Toffoli, iToffoli, and Fredkin gates. We analyze both triangular and linear qubit configurations and numerically optimize the control parameters for the three-qubit and single-qubit gates to achieve high-fidelity circuit implementations. Our results show that employing multiqubit gates can substantially reduce the circuit depth and gate count required to realize target circuits compared to the conventional single- and two-qubit gate approach.