Waveguide-array-based multiplexed photonic interface for atom array

TL;DR

The paper addresses the need for high-rate entanglement distribution in quantum networks by proposing a scalable photonic interconnect built around a glass-based photonic integrated circuit (PIC) with a 32-channel waveguide array. It demonstrates multiplexed single-photon guiding from a 10-site neutral-atom array to 10 corresponding waveguides, achieving net coupling efficiencies of roughly 0.3%–1.2% per channel with low inter-channel crosstalk, and confirms atom–photon correlations with a polarization visibility of 0.87. The results establish a compact, integrated platform capable of distributing multiplexed atom–photon entanglement, a critical component for networked quantum processors and long-distance quantum communication. The work highlights pathways for improvement via aberration-correction and microlens cavity integration to boost efficiency and reduce the required atom spacing, enhancing scalability for fault-tolerant distributed quantum computing.

Abstract

The growing demand for high-capacity quantum communication and large-scale quantum computing underscores the importance of networking quantum processing units via multiplexed photonic channels. A neutral atom array with multiplexed atom-photon entanglement is a promising platform for its realization. Here, we demonstrate a key multiplexed photonic interface guiding the photons from an atom array to a single-mode waveguide array fabricated on a glass-based photonic integrated circuit. Remarkable 10 channels out of the 32-channel waveguide array with 25 $μ$m pitch couple to photons from 10 sites of the atom array with Rydberg gate-enabled separation. Based on the observed correlation between the atomic states and the polarization of the photon with a visibility of 0.87, we anticipate its applicability to a large-scale multiplexed atom-photon entanglement generation for networking quantum processing units.

Figures (4)

• Figure 1: Experimental setup. Our $^{87}$Rb atom array is shown by red circles at the center of the chamber. The optical tweezer array for trapping atoms is formed by spatial light modulator (SLM) with 852-nm laser (drawn with orange color). Emitted photons at 780 nm (drawn with red color) are coupled to the waveguide array through an objective lens with $\mathrm{NA}=0.7$ and multiple lens, and then detected by multichannel superconducting nanostrip single-photon detectors (SNSPDs). The shortpass filter passes 780-nm photons and reflects 852-nm laser for optical tweezers, thereby suppressing stray light to a negligible level. Excitation and intialization beams (pump 2-1, 2-2 and 1-1) propagate along the $x$ axis, while the applied magnetic field defines the quantization axis along $z$ axis. (a) Energy level diagram of atom-photon entanglement generation involving atomic Zeeman sublevels and photonic polarization states. (b) Polarization analyzer for the collected photons. It consists of a Wollaston prism, a quarter-wave plate (QWP), and a half-wave plate (HWP). Horizontal and vertical polarized photons are sent to SNSPD channels $D_\mathrm{H}$ and $D_\mathrm{V}$, respectively.
• Figure 2: Optimization of optical tweezers by photon counting experiment. (a) Schematic of scanning the atoms by optical tweezers. (b) Histograms of photon counts for atom site 1 at position $r_{\mathrm{ref}}=(0.25, 0.00, 0.00)~\mathrm{\mu m}$ (gray) and $r_{\mathrm{ref}}=(-0.25, 0.00, 0.00)~\mathrm{\mu m}$ (black). The black histogram corresponds to the maximized coupling efficiency. (c) 2D map of histograms obtained by scanning the optical tweezer for atom site 0 in the $xy$-plane on a $9\times9$ grid. The face color represents the total photon counts normalized by the maximum counts. (d) 2D maps of 10 atom sites measured at $z_\mathrm{ref} = -2.36, 0.00, 2.56~\mathrm{\mu m}$. The locations of atoms reflect actual atom spacing. (e) Normalized maximum photon counts obtained as a function of tweezer position along the $z$-axis.
• Figure 3: Characterization of waveguide-array-coupled single photons. (a) Temporal profiles of spontaneous emission from atom sites 0-9. (b) Map of normalized photon counts from atom sites to the waveguide array. Diagonal elements represent the case where the photons emitted from atom site $i$ couple to waveguide $i$. Atom-photon correlation measurement by rotating the polarization of the photons in circular polarization basis (c) and in linear polarization basis (d).
• Figure 4: Experimental sequence for photon generation into waveguide array. (a) Fluorescence measurement in Sec. \ref{['sec:single_photon_experiment']}. The cycle includes atom loading, initial atom measurement, state initialization, excitation, and final atom measurement. The photon generation process, in which photon detection is also performed for 10$~\mathrm{\mu s}$, is repeated 40 times. (b) Atom-photon correlation measurement in Sec. \ref{['sec:atom_photon_correlation']}. The generation process is repeated up to 30 times. When the photon detection event happens, the projection measurement of the atomic state starts.