Charged quantum dot micropillar system for deterministic light-matter interactions

Quantum dots (QDs) are semiconductor nanostructures in which a three-dimensional potential trap produces an electronic quantum confinement, thus mimicking the behavior of single atomic dipole-like transitions. However, unlike atoms, QDs can be incorporated into solid-state photonic devices such as cavities or waveguides that enhance the light-matter interaction. A near unit efficiency light-matter interaction is essential for deterministic, scalable quantum-information (QI) devices. In this limit, a single photon input into the device will undergo a large rotation of the polarization of the light field due to the strong interaction with the QD. In this paper we measure a macroscopic ($\sim 6^{\circ }$) phase shift of light as a result of the interaction with a negatively charged QD coupled to a low-quality-factor ($Q\sim 290$) pillar microcavity. This unexpectedly large rotation angle demonstrates that this simple low-$Q$-factor design would enable near-deterministic light-matter interactions.

Figure 1

(a) Schematic of the QD micropillar system with the available decay channels. (b) Available circular transitions for a negatively charged QD and the corresponding excitons created, along with the corresponding rotation of linearly polarized coherently scattered photons. (c) Photoluminescence (PL) spectrum of the micropillar under consideration at $T=12$ K. The CM may be seen and the QD on top of the half maximum point of the CM. Inset: PL spectrum of the QD under lower off-resonant excitation power. (d) Schematic of the experiment. The laser polarization is set with a linear polarizer (LP). The measured light is split on a nonpolarizing beamsplitter (BS) into two different measurement paths. The first path, for the identification of the transitions, is selected using a polarizing beamsplitter (PBS) for the cross-polarized resonant scattering (detection path on the left). The second path is incident on a phase shift interferometer setup (on the right), where a quarter wave plate ($\lambda /4$, QWP) and a half wave plate ($\lambda /2$, HWP) are used to rotate the light to the correct measurement basis and a Soleil-Babinet compensator (SB) is used to account for any birefringence present and to calibrate our interferometer. Avalanche photodiodes (APDs) are used to record the signal.

Figure 2

(a) Photon counts using the resonant scattering technique detected in the cross-polarized arm. The two circular transitions are indicated, with arrows to indicate the spin orientation. (b) Experimental data for the phase shift (red points) overlaid with the theoretical fit (blue line) after incorporating jitter and accounting for the thermalization between the spin states. The dashed lines correspond to the resonant frequency for each transition.

Figure 3

(a) Measured lifetime of the QD transition under study. (b) The black circles represent the $1/T_1$ quantity. The black star next to the black circle in the middle denotes the QD under study. The lifetimes where measured under pulsed $p$-shell excitation. ${\mathrm{\Gamma }}_t/{\gamma }_{\mathrm{hom}}$ was simulated and the simulated value for $1/T_1$ is plotted fitting for $T_{1\mathrm{hom}}=710$ ps (red curve). $T_{1\mathrm{hom}}=710$ ps is in agreement with lifetime measurements performed on similar wavelength QDs without an etched structure from the same wafer. The blue curve is the ratio $\gamma /{\gamma }_{\mathrm{hom}}$ as it is simulated for this structure.