High-efficiency vertical emission spin-photon interface for scalable quantum memories

Abstract

We present an efficient spin-photon interface for free-space vertical emission coupling. Using a \rev{dipole model}, we show that our design achieves a far-field collection efficiency of 96\% at the numerical aperture of 0.7 with a 95\% overlap to a Gaussian mode. Our approach is based on a dual perturbation layer design. The first perturbation layer extracts and redirects the resonant mode of a diamond microdisk resonator around the optical axis. The second perturbation layer suppresses side lobes and concentrates most of the light intensity near the center. This dual-layer design enhances control over the farfield pattern and also reduces alignment sensitivity. Additionally, the implemented \rev{dipole model} performs calculations \( 3.2 \times 10^6 \) times faster than full-wave FDTD simulations. These features make the design promising for quantum information applications.

Figures (7)

• Figure 1: (a) 3D Design: A schematic representation of a spin-photon interface consisting of a disk resonator coupled to a dual-grating structure. The orange mark represents the point dipole source used to excite the disk mode. (b) Cross-sectional view of the design. On the right, the nearfield (NF), intermediate field (IF), and farfield (FF) are shown at different heights. (c) Hexagonal lattice unit cell and local $(u,v)$ coordinate system. The blue symmetry lines identify a reduced-symmetry domain (purple) used to parameterize alignment; points A and B are key alignment points $(u,v)$ exhibiting high radial symmetry. A zoom-in highlights the WGM–grating interaction region. Expanding hexagonal traces from a center lattice point in a triangular lattice: for $n=3$, 18 lattice holes form the perimeter of the hexagon; 10 holes efficiently interact with the WGM of the resonator. The microdisk is shown in light blue
• Figure 2: Cross sections of the intermediate field (dashed red) and farfield (blue) intensity distributions as a function of numerical aperture, with charges: (a) $L = 0$, (b) $L = 1$, (c) $L = 2$, and (d) $L = 3$.
• Figure 3: (a) and (b) illustrate the intermediate and far-field distributions for two different grating alignment configurations. The leftmost schematics depict the structural alignment, where the grating is either fixed or translated relative to the disk resonator. The middle panels show the simulated far-field distributions obtained using the FDTD method and the Dipole Model. The rightmost plots present the collection efficiency as a function of the numerical aperture for both models.
• Figure 4: Collection efficiency as a function of the grating alignment. (a) The collection efficiency for different alignments of the first grating layer, while the second grating layer is fixed. The farfield pattern is shown for each alignment configuration. (b) The collection efficiency for different alignments of the first grating layer, while the second grating layer is fixed. The farfield pattern is shown for each alignment configuration. We parameterize alignment by $s=\Delta/a \in [0,1]$, where $\Delta$ is the lateral offset of the reference scatterer from the optical axis and $a$ is the lattice constant. $s=0$ is perfect alignment (Configuration A in Fig. \ref{['figure1']}(c)), and $s=1$ is full misalignment (Configuration B in Fig. \ref{['figure1']}(c)). For completeness, $\eta_{\mathrm{tot}}$ values differ by $<0.5\%$ from $\eta_{\mathrm{col}}$ over the sweep; numerical values are provided in the text/SI.
• Figure 5: The far-field distribution for different dipole orientations. (a) $\theta=90, \phi=90$, (b) $\theta=45, \phi=90$, (c) $\theta=25, \phi=90$, (d) $\theta=10, \phi=90$, (e) $\theta=0, \phi=90$, (f) $\theta=90, \phi=0$.