Chiral Quantum Optics with Scalable Quantum Dot Dimers

TL;DR

This work addresses scaling challenges in chiral quantum optics by enabling independent electrical tuning of multiple quantum emitters embedded in a glide-plane photonic crystal waveguide. It introduces ion implantation in the p-doped layer to create a non-etch high-resistivity barrier that preserves optical mode integrity while enabling Stark tuning of separate quantum dots. The authors demonstrate two chirally coupled QDs with spectral stability under Stark tuning and characterize spin-dependent photon correlations $g^{(2)}(\tau)$ that agree with a waveguide-QED model, confirming preserved chirality and coherent emitter interference. Collectively, these results establish a scalable platform for multi-emitter chiral networks with potential impacts on quantum communication and repeater architectures, including deterministic entanglement and long-time synchronization.

Abstract

We present a scalable method for electrically tuning multiple spatially separated quantum dots embedded in photonic crystal waveguides. Ion implantation into the top p-doped layer of a p-i-n diode creates high-resistivity tracks, providing electrical isolation between adjacent regions. Unlike physical etching, this method preserves the guided-mode profile of the photonic crystal without introducing significant scattering, limiting refractive index perturbations to below 0.001 with 0.01% additional loss. In contrast, physical etching can reduce single-band transmission by more than 30% for an etch width of 100 nm. We demonstrate the applicability of our approach using quantum dots embedded in a glideplane photonic crystal waveguide, controlling the detuning between different spin-state combinations of two highly chiral quantum dots coupled to the same mode. Second-order photon correlation measurements provide a sensitive probe of the chirality-dependent photon statistics, which are in good agreement with a waveguide-QED master equation model. Our results mark an important step towards scalable, multi-emitter architectures for chiral quantum networks.

Figures (4)

• Figure 1: (a) Schematic cross-section of p-i-n membrane structure used for ion implantation. (b)(i) SEM image of the photonic crystal waveguide. (b)(ii) Top down SEM of GPWG highlighting the implanted region (500nm in width) seen as pseudo-colour green strip across the center of the waveguide.(c) Photonic band structure of the glide-plane waveguide; the shaded yellow region corresponds to the simulated band in (d). (d)(i, ii) Simulated transmission loss as a function of refractive-index ($\Delta n$) and extinction-coefficient ($\Delta k$) perturbations for 100nm and 500 nm implantation depths, respectively.
• Figure 2: (a-c) Confocal photoluminescence (PL) images showing emission from two electrically isolated regions of a diode under different applied biases. (a) Both left and right sections are forward biased at +2 V, resulting in emission across the full device. (b,c) Independent tuning demonstrated by locally forward biasing one section (+2 V) while reverse biasing the other (--$2$ V), leading to selective quenching of emission in the reverse-biased region. (d) Measured IV characteristics, comparing vertical IV across membrane (blue) and lateral IV across the implanted barrier (red),showing strong suppression of lateral current.
• Figure 3: (a) Schematic of the chiral PhC waveguide showing two spatially separated quantum dots (QD$_1$ and QD$_2$) embedded on either side of an implanted isolation barrier. The $\sigma^{+}$ and $\sigma^{-}$ spin transitions couple into opposite directions due to spin–momentum locking. (b,c) PL maps acquired from the right propagating mode (RHS) and left propagating mode (LHS), showing Stark tuning of Zeeman split QD transitions under applied voltage. Colored dashed lines track the $\sigma^\pm$ transitions of each dot.
• Figure 4: (a) Spin configurations for three two-emitter correlation measurements where light is collected from the left hand side of the waveguide shown in Fig. \ref{['fig3']}(b) (i) the $\sigma^{-}$ of QD1 and QD2 are measured, (ii) the $\sigma^{-}$ state of QD1 and $\sigma^{+}$ of QD2 are measured, (iii) the $\sigma^{+}$ state of QD1 and $\sigma^{-}$ of QD2 are measured (b) Photoluminescence spectra demonstrating the tuning of various spin pairs into resonance. (i) $\sigma^{-}_{1}$ + $\sigma^{-}_{2}$, (ii) $\sigma^{-}_{1}$ + $\sigma^{+}_{2}$, (iii) $\sigma^{-}_{2}$ + $\sigma^{+}_{1}$, with red-shaded regions indicating the spectral windows used for filtering prior to correlation measurements. (c) Second-order photon correlation functions $g^{(2)}(\tau)$ for the spin state combinations in (a), showing theoretical fits (solid lines) and experimental data (black dots). The quantum limit, $g^{(2)}(\tau)=0.5$, is indicated by the red dashed line.