FAPESP-EPSRC: Multi-species Ion-Photon Interface for Distributed Quantum Computing
Lead Research Organisation:
University of Sussex
Abstract
Distributed Quantum Computing is one of the most promising schemes towards large-scale quantum computing. Here smaller scale quantum information processors (QIP) or nodes are linked together to form a large-scale network with significant computational power. Crucial for this is a fast, high-fidelity, and highly efficient interface that can operate in combination with the photonic links. A promising way to do so in ion-based quantum computers is to employ two ion species: One ion species (referred to as QIP ions) is dedicated to QIP tasks and as memory, while the other species (referred to as QN ions) is exclusively used to establish connections between the quantum processor and the network through photonic links. This added ion species requires an additional local step to transfer the quantum states of the QN ion to the QIP ion. Hence, the conventional, step-by-step process of generating ion-ion photon entanglement between the QIP nodes is as follows:
1. Generation of local ion-photon entanglement.
2. Projective measurement of the joint photonic state to establish ion-ion entanglement.
3. Transfer of the entangled states locally from the QN to the QIP ion using mixed species gates.
4. Use of ion-ion entanglement as a resource for teleportation.
Although theoretically sound, this stepwise approach presents significant experimental challenges. The introduction of sequential additional steps is associated with the accumulation of imperfections. In this research project, our primary goal is to establish entanglement between the QIP ion and the photon in a single step by utilizing the QN ion as a quantum information bus. This approach will reduce the decoherence caused by the QN ions. In this novel approach, the QN ion will be coupled to an optical cavity with its qubit states interacting with two orthogonal polarization modes of the cavity through a Raman transition. Simultaneously, we will perform a Mølmer–Sørensen gate between the QIP and QN ions. This operation will result in an entangled state between the QIP ion and the photon’s polarisation, without involving the final state of the QN ion. Consequently, the QN ion will serve only as a bus for the entanglement process between the QIP ion and the photon.
1. Generation of local ion-photon entanglement.
2. Projective measurement of the joint photonic state to establish ion-ion entanglement.
3. Transfer of the entangled states locally from the QN to the QIP ion using mixed species gates.
4. Use of ion-ion entanglement as a resource for teleportation.
Although theoretically sound, this stepwise approach presents significant experimental challenges. The introduction of sequential additional steps is associated with the accumulation of imperfections. In this research project, our primary goal is to establish entanglement between the QIP ion and the photon in a single step by utilizing the QN ion as a quantum information bus. This approach will reduce the decoherence caused by the QN ions. In this novel approach, the QN ion will be coupled to an optical cavity with its qubit states interacting with two orthogonal polarization modes of the cavity through a Raman transition. Simultaneously, we will perform a Mølmer–Sørensen gate between the QIP and QN ions. This operation will result in an entangled state between the QIP ion and the photon’s polarisation, without involving the final state of the QN ion. Consequently, the QN ion will serve only as a bus for the entanglement process between the QIP ion and the photon.