Deterministic preparation of W states via spin-photon interactions

Abstract

Spin systems such as silicon and nitrogen-vacancy centers in diamond, quantum dots, and quantum dot molecules coupled to optical cavities appear to be key elements for creating quantum networks by not only constituting the nodes of the network but also assisting the creation of photonic networks. Here we study the deterministic preparation of arbitrary-size W states with spin systems. We present an efficient operation on three qubits, with two being the logical qubits and one being the ancillary qubit, where no interaction between the logical qubits is required. The proposed operation can create a W-type Einstein-Podolsky-Rosen (EPR) pair from two separable qubits and expand that EPR pair or an arbitrary-size W state by one, creating a W-like state Taking this operation as the fundamental building block, we show how to create a large-scale W state out of separable qubits or double the size of a W state. Based on this operation and focusing on nitrogen-vacancy centers in diamond as an exemplary spin system, we propose a setup for preparing W states of circularly polarized photons, assisted by a single-spin qubit, where no photon-photon interactions are required. Next, we propose a setup for preparing W states of spin qubits of spatially separated systems, assisted by a single photon. We also analyze the effects of possible imperfections in implementing the gates on the fidelity of the generated W states. In our setups, neither postmeasurement nor postprocessing the states of spin or photonic qubit is required. Our setups can be implemented with current technology, and we anticipate that they will contribute to quantum science and technologies.