Programmable Quantum Photonic Interfaces for Quantum Networking

TL;DR

This work addresses programmable interfaces for translating memory photons to telecom while controlling spatial modes, aiming to reduce cascaded losses and enable in-situ reconfiguration. It introduces a structured pump that writes a virtual Bragg grating within a LiNbO3 multimode resonator to unify spectral conversion and spatial routing. Using a diamond-LiNbO3 hybrid ring, the authors demonstrate readout via difference-frequency generation to telecom and write-in via sum-frequency generation controlled by pump holograms, achieving bidirectional operation. Numerical validation with FDTD confirms angular-momentum selection rules and high spatial coupling efficiency (≈93%), illustrating reconfigurable far-field patterns and establishing a practical path toward scalable quantum networking with hardware-free reconfiguration.

Abstract

Quantum networks require interfaces translating memory photons to telecom wavelengths while controlling spatial modes; tasks performed by separate components today. We present a programmable alternative: a structured pump writes a virtual Bragg grating enabling simultaneous spatio-spectral conversion and real-time controlling of emission. Using a LiNbO$_3$ whispering-gallery resonator, we demonstrate 93\% spatial coupling and bidirectional conversion between 736\,nm and 1347\,nm. This reconfigurable interface eliminates cascaded losses and hardware modifications.

Figures (6)

• Figure 1: (a) Concept and device: a shaped, $N$-site pump writes a virtual Bragg grating on a $\chi^{(2)}$ ring co-axial with a diamond WGM hosting a SiV (parameters in Supplementary Table 2). (b) DFG (read-out) spectrum showing telecom emission at $\lambda_3=1347\,\mathrm{nm}$; dominant mode $(M,p,q)=(21,1,2)$ at 736 nm. (c) SFG (write-in) spectrum around 738 nm when a Gaussian fiber mode and the $N=23$ pump excite the cavity.
• Figure 2: Programmable far field. Each panel plots the normalised intensity $I(\theta,\phi)$ for $0\leq\theta\leq30^{\circ}$ (radial axis) and $0\leq\phi<2\pi$ (horizontal axis); color bars are normalised to the peak of each simulation. Varying the pump sampling $N$ at fixed $M=21$ (dominant harmonic $\ell=1$) changes the azimuthal periodicity $2|M-\ell N|$, switching between two-lobe patterns, on-axis brightening ($|M-\ell N|=2$), and multi-lobe morphologies, consistent with the selection rules and Eq. \ref{['equation6']}.
• Figure 3: (a) DFG readout spectrum: converted telecom peak at $\lambda_3=1347$ nm driven from the $(M,p,q)=(21,1,2)$ WGM. (b) Far-field intensity for $N=23$ from FDTD; (c) analytic bright-mode prediction for the same case. (d) SFG write-in spectrum around $\lambda_1\approx736$ nm under the same pump. (e) Spatial mode of the coupled WGM (normalized intensity). (f) Bright-mode population versus azimuthal interaction length for the SFG process; color scales in panels (b) to (e) are normalized to their respective maxima.
• Figure S1: Polarization pathway (theory/simulation). Top: focal-plane polarization example in which the pump is azimuthal, the WGM/signal is radial, and their $\chi^{(2)}$ product produces a circular nonlinear polarization on the ring. Bottom: far-field RHCP/LHCP maps (analytic model with $M=20$, $N=17$, $\ell=1$) and line cut showing the R/L power split within the objective NA (cyan circle).
• Figure S2: Feasibility of selection-rule harmonics in $(N,\ell)$ space for the present SLM/optic ($p=12.5\,\mu\mathrm{m}$, $f=1.5$ mm, $P_{\max}=6$ mm, $\lambda_{\mathrm{res}}=736$ nm, $\mathrm{NA}=0.95$, $n_{\mathrm{eff}}=1.7$). Points satisfy $|m'|/R<k_0\mathrm{NA}$ for $m'=\ell N\pm M\pm2$. Color shows the pump harmonic’s $|J_m|^2$ fraction inside NA; $\Delta m=\pm2$ cases (with on-axis $m'=0$ components) are highlighted.