Speakers
Description
Cavity-assisted photon-mediated protocols are a promising approach for generating remote entanglement between trapped-ion nodes, a key requirement for scalable quantum networks. Time-bin encoding offers robustness against polarisation drift and fibre-induced decoherence [1], while optical cavities enhance photon extraction via the Purcell effect, addressing a major bottleneck in heralded entanglement generation schemes [2]. A recently proposed [3] protocol for 88Sr+ combines these advantages using cavity-assisted vacuum-stimulated Raman adiabatic passage (vSTIRAP) to generate time-bin encoded ion–photon entanglement.
In this work, we perform a detailed theoretical and numerical analysis of the proposed cavity-assisted, time-bin encoded heralded ion-ion entanglement protocol. We focus on quantifying both the entanglement generation rate and fidelity and identifying the dominant physical error mechanisms arising from realistic atom-laser-cavity dynamics. The protocol is analysed at the level of single attempt cycles, including optical pumping, quadrupole pulses, and photon generation via vSTIRAP, followed by two-photon interference and heralding. We also investigate motion-induced errors originating from recoil during photon emission which introduce spin-motion-photon entanglement. Using recent kick-operator-based descriptions of recoil processes as developed in Refs. [4,5], we evaluate their impact on entanglement fidelity in our architecture.
The system dynamics are modelled using a Lindblad master equation formalism, incorporating all relevant atomic sublevels and spontaneous emission channels. Off-resonant couplings and multi-level effects are explicitly included to capture leakage into non-target states. To evaluate the emitted photon wave-packets, we combine input-output theory in the Markov approximation with a non-Hermitian (no-jump) evolution approach, allowing extraction of the complex temporal mode amplitudes required to assess indistinguishability.
Closely following Ref. [6], we derive expressions for the herald-conditioned ion-ion density matrix in the time-bin encoding basis and show that the resulting entanglement fidelity is directly determined by the overlap of the emitted photon wave packets. We identify residual population in the D3/2 manifold after optical pumping, off-resonant excitation during coherent operations and differential mode cavity lengths between nodes as key sources of fidelity degradation. We calculate that static cavity length differences of ~1pm between the nodes correspond to a ~20% bell-state error, while off-resonant interactions correspond to a <1% bell-state error. We obtain an estimated attempt cycle duration of 5 us. These results provide the first systematic quantitative analysis of a cavity-assisted, time-bin encoded ion–ion entanglement scheme, offering practical guidance for experimental optimisation and parameter selection.
References
[1] S. Saha et al., “High-fidelity remote entanglement of trapped atoms mediated by time-bin photons”, Nature Communications, 2025.
[2] S. Gao, “Optimization of Scalable Ion-Cavity Interfaces for Quantum Photonic Networks”, DPhil Thesis, University Of Oxford, 2023.
[3] W. J. Hughes, “Towards scalable ion trap nodes for cavity-enhanced quantum networking”, DPhil Thesis, University Of Oxford, 2022.
[4] D. P. Nadlinger and J. Apolín, “Recoil-induced errors and their correction in photon-mediated entanglement between atom qubits,” 2025.
[5] S. Kikura et al., “Taming the Recoil Effect in Cavity-Assisted Quantum Interconnects,” 2025.
[6] D. P. Nadlinger, “Device-Independent Key Distribution between Trapped-Ion Quantum Network Nodes”, DPhil Thesis, University Of Oxford, 2022.
| Academic level | Master's Student |
|---|