Perfect quantum state transfer in a superconducting qubit chain with parametrically tunable couplings

Faithfully transferring the quantum state is essential for quantum information processing. Here we demonstrate a fast (in 84 ns) and high-fidelity (99.2%) transfer of arbitrary quantum states in a chain of four superconducting qubits with nearest-neighbor coupling. This transfer relies on full control of the effective couplings between neighboring qubits, which is realized only by our parametrically modulating the qubits without increasing circuit complexity. Once the couplings between qubits fulfill a specific ratio, perfect quantum state transfer can be achieved in a single step, and is therefore robust to noise and accumulation of experimental errors. This quantum state transfer can be extended to a larger qubit chain and thus adds a desirable tool for future quantum information processing. The demonstrated flexibility of the coupling tunability is suitable for quantum simulation of many-body physics, which requires different configurations of qubit couplings.