Parity-Dependent State Transfer and Many-Qubit Entanglement Generation on a Superconducting Qubit Chain

Superconducting qubit devices have recently demonstrated high-fidelity operations, high coherence times and improved scalability, making them a leading platform for quantum computing. However, practical applications require the efficient generation of many-qubit entangled states, incurring large overheads in single- and two-qubit gates as qubit connectivity is generally limited to nearest-neighbor pairs. Nonetheless, by evolving the system under simultaneous local interactions, one can realize effective non-local multi-qubit operations, efficiently generating entanglement. In this work, we operate a circuit of six fixed-frequency transmons with tunable couplers and control the couplings via simultaneous parametric drives. We engineer the drive amplitudes and frequencies in order to implement a quantum state transfer protocol, in which excitations are coherently transferred between distant qubits. We observe the parity-dependent property of the transfer, where the number of excitations within the chain controls the phase of the transferred state. Finally, we utilize this property to prepare multi-qubit GHZ states with Hadamard gates and a single transfer operation, demonstrating efficient entanglement generation.