One-step transfer or exchange of arbitrary multipartite quantum states with a single-qubit coupler
The transfer or exchange of multipartite quantum states is critical to the realization of large-scale quantum information processing and quantum communication. In this work, we demonstrate that by using a single quantum two-level system—a qubit—as a coupler, arbitrary multipartite quantum states (either entangled or separable) can be transferred or exchanged simultaneously between two sets of qubits. During the entire process, the coupler remains unexcited minimizing the effect of coupler decoherence on the process. This feature allows one to use qubits with rapid frequency tunability and a large range of frequency tuning, such as phase qubits, as couplers. Our findings offer the potential to significantly reduce the resources needed to construct and operate large-scale quantum information networks consisting of many multiqubit registers, memory cells, and processing units.