Electron juggling: Approaching the atomic physics limit of the attempt rate in trapped ion photonic interconnects

TL;DR

The paper tackles the bottleneck of slow state preparation in trapped-ion photonic interconnects by introducing 'electron juggling', a method that replaces slow optical pumping with rapid, alternating circularly polarized pulses to directly drive the $|S_{1/2}\rangle \leftrightarrow |P_{1/2}\rangle$ transition. A Lindblad-based model including polarization impurities and repumping dynamics assesses REG rate and fidelity, showing that ideal conditions yield $R_{\mathrm{REG}}$ well above $10^3\,\mathrm{s}^{-1}$ for multiple ion species, with Ba$^+$ nearing but not exceeding this threshold, and realistic latencies still suppress REG rates by a modest amount while maintaining fidelities around $0.984$–$0.986$. The work demonstrates that REG performance can approach the atomic-physics limit and potentially exceed 1,000 s$^{-1}$ under favorable hardware, providing a practical path to fast, high-fidelity remote entanglement in modular quantum networks. It also outlines repumping strategies tailored to different ion species, ensuring continuous operation without large fidelity costs, and offers a framework for evaluating speed-versus-impurity tradeoffs in photonic interconnects.

Abstract

Photonic interconnects are a key technology for scaling up atomic based quantum computers. By facilitating the connection of multiple systems, high-performance modular quantum processing units may be constructed to perform deeper and more useful algorithms. Most previous implementations of photonic interconnects in trapped ions utilize the scheme of preparing a state, exciting it, and collecting single photons from decays of the excited state. State preparation is responsible for the vast majority of the total attempt time, often taking hundreds of nanoseconds to several microseconds. Here, we describe and analyze a novel technique called ``electron juggling" to speed up photonic interconnects by reducing the state preparation step substantially. Using a theoretical framework, we illustrate how this scheme can significantly increase remote entanglement generation rates, approaching the atomic physics limit of the attempt rate in trapped-ion photonic interconnects. Our results indicate that this scheme holds the possibility of achieving remote entanglement generation rates of over 1,000 Bell pairs per second.

Figures (4)

• Figure 1: Partial atomic structure of ions considered in this paper consisting of a ground $S_{1/2}$ manifold and an excited $P_{1/2}$ manifold, each with two Zeeman sublevels. We label the $S$ ($P$) sublevels' state vectors with z-angular-momentum projection quantum numbers $m_J = \pm1/2$ as $|S_\pm\rangle$ ($|P_\pm\rangle$). The possible transitions are shown as blue arrows, with the corresponding Clebsch-Gordan coefficients next to the relevant arrows.
• Figure 2: Schematic depiction of the electron juggling scheme. For clarity, we assume the ion is excited by $\sigma^+$ light in Step 1. The ion's internal population distribution at each step is characterized by filled orange circles, whose radii are roughly proportional to the probability the ion occupies that energy level. Dotted circles correspond to population flux out of the associated energy level. Photon detection takes place during steps 2, 4, ... etc. If photons successfully herald REG on one of these steps, the procedure is halted.
• Figure 3: Results of the electron juggling simulation, assuming no latencies and no polarization impurities. The REG rate (solid curves) in Bell pairs per second and fidelity (dotted curves) are plotted against the photon detection window width. The current trapped ion REG rate record, 250 s$^{-1}$OReilly2024 is represented by the black horizontal line. The fidelity sharply drops at small detection windows, despite assuming perfectly polarization-pure excitation pulses. This is due to residual population in the "wrong" $P_{1/2}$ sublevel for very rapid attempts.
• Figure 4: Results of the electron juggling simulation including polarization impurity and attempt latencies. The REG rate in Bell pairs per second is plotted against the photon detection window width (note the total attempt time will be 100 ns plus this, since we assume 100 ns of latencies). The current trapped ion REG rate record of 250 s$^{-1}$OReilly2024 is represented by the black horizontal line. All species can achieve at least three times this with electron juggling.