Implementation of Fractional State Transfer on a Superconducting Qubit Chain

Superconducting circuits are a promising candidate architecture for quantum computation due to their high coherence times and high-fidelity control, however, qubit connectivity is limited to nearest-neighbour local interactions. Nonetheless, recent studies show that simultaneous local interactions can be harnessed to generate multi-qubit operations and efficiently generate many-body entanglement. In this work we operate a superconducting circuit qubit chain, with fixed-frequency transmon qubits, and flux tunable transmon couplers. By simultaneous parametric drive of the tunable couplers we generate effective multi-qubit interactions and transfer excitations from one end of the chain to the other end, an operation known as perfect state transfer. . In this work we implement perfect state transfer on a superconducting circuit qubit chain, where an excitation on one end of the chain is transferred to the other end, based on an effective multi-qubit interaction. Furthermore, we demonstrate fractional state transfer, where only a fraction of the state is transferred, as controlled by the frequency and strength of parametric drives on the couplers. We show how this protocol can be used to efficiently generate entangled states and multi-qubit operations. Finally, good agreement with theoretical predictions suggests the scalability of this protocol to longer qubit chains.