Topologically protected spatial-phase mismatching for cavity-enhanced quantum memories

Microphotonic quantum memory presents a promising avenue for miniaturizing and scaling up memories for quantum network applications. While conventional microphotonic cavities can provide enhanced light-matter-interaction to improve the memory efficiency, they are constrained by inherent limitations when utilizing the quantum memory protocol of the revival of silenced echo (ROSE). These limitations primarily arise from the high sensitivity to cavity fabrication imperfections, which scatter stored optical modes into alternate modes and cause a subsequent reduction in efficiency. In this study, we propose that the incorporation of robust edge states and defect states in topological photonic crystals offers a solution to overcome this inherent limitation. The spatial-phase-mismatching effect that underlies ROSE is topologically protected, effectively mitigating the distortion of stored optical states caused by imperfection scattering and improves the memory efficiency.

Figure 1

Integrated topological quantum memory scheme. (a) Left, memory pulse sequence: red, a signal pulse with spatial phase ${\varphi }_0$; blue, two control $\pi$ pulses with spatial phase: ${\varphi }_1$ and ${\varphi }_2$, respectively; rainbow, the photon echo. Right, a topologically protected cavity-waveguide memory, where $\kappa$ and $\gamma$ are the coupling coefficient of the cavity and the cavity intrinsic loss, respectively. (b) Left, schematics of a standing-wave cavity, which cannot provide the phase-mismatching effect for ROSE. Right, schematics of a conventional WGM cavity. A defect in the cavity causes the scattering of a clockwise propagating mode into a counterpropagating mode. (c) Comparison of electric field distribution (in log scale) without (left) and with (right) a defect in a WGM cavity.

Figure 2

Valley-dependent edge states in topological photonic crystal cavity. (a) Left, dispersion of the valley-dependent edge states for two distinct domain walls as shown on the right. Here, the black dashed line corresponds to a traveling-wave mode with eigenfrequency $f_0=196.73486\mathrm{THz}$ ($1.5\mu \mathrm{m}$) of the topological cavity in (b). Right, the structure of supercells comprised of two types of photonic crystal named type I and type II. Their field distributions (in log scale) around the two different interfaces. The first one corresponds to the red dispersion curve on the left and the second one corresponds to the blue. (b) Transmission spectra for the triangular cavity. Inset: The field distribution (in log scale) of the topological cavity mode at the resonant frequency $f_0$. The side length of the cavity is $12a$.

Figure 3

Mode analysis of topological waveguide-cavity system. (a), (b) Cavity field distributions (in log scale) that excited by left and right circularly polarized chiral source placed on the left and right sides of the waveguide, respectively. (c), (d) Up, the zoomed field distributions corresponding to the black dashed boxes in (a), (b). The high-field-intensity points appear in same locations. Down, the phase distribution corresponding to the black dashed boxes in (a), (b). The phase vortex (black arrows) at the relative positions of the valley photonic crystal interface is opposite.

Figure 4

Topological photonic crystal quantum memory. (a) Output pulse sequences of photon echo schemes based on the imperfect WGM cavity in Fig. 1 (upper) and topological photonic crystal cavity (lower). The red dashed lines indicate the positions of the first (unwanted) and second echoes. (b) The schematic diagram of the cavity-waveguide coupling system with missing, shift, incompletion defects in different locations as noted. (c) The robust field distributions (in log scale) with the aforementioned defects.