Accessing the dark exciton spin in deterministic quantum-dot microlenses

Abstract

The dark exciton state in semiconductor quantum dots constitutes a long-lived solid-state qubit which has the potential to play an important role in implementations of solid-state based quantum information architectures. In this work, we exploit deterministically fabricated QD microlenses with enhanced photon extraction, to optically prepare and readout the dark exciton spin and observe its coherent precession. The optical access to the dark exciton is provided via spin-blockaded metastable biexciton states acting as heralding state, which are identified deploying polarization-sensitive spectroscopy as well as time-resolved photon cross-correlation experiments. Our experiments reveal a spin-precession period of the dark exciton of $(0.82\pm0.01)\,$ns corresponding to a fine-structure splitting of $(5.0\pm0.7)\,\mu$eV between its eigenstates $\left|\uparrow\Uparrow\pm\downarrow\Downarrow\right\rangle$. By exploiting microlenses deterministically fabricated above pre-selected QDs, our work demonstrates the possibility to scale up implementations of quantum information processing schemes using the QD-confined dark exciton spin qubit, such as the generation of photonic cluster states or the realization of a solid-state-based quantum memory.Comment: 5 pages, 3 figure

Emission properties and temporal coherence of the dark exciton confined in a GaAs/AlxGa1−xAs quantum dot

“…The low emission of dark excitons (DEs) in confined semiconductor quantum dots (QDs) can be easily detected nowadays thanks to high spatial resolution spectroscopy, resonant fluorescence experiments, and coupling to photonic cavities [1]. Due to spin conservation rules, a DE that is formed by one electron and one hole with parallel spins cannot absorb or emit a photon.…”

Engineering Purcell factor anisotropy for dark and bright excitons in two dimensional semiconductors

“…The combination of these two effects gives rise to strong interlayer emission from the vdW disk resonators. Tobias Heindel et al [24] exploit deterministically fabricated quantumdot microlenses to boost photon extraction and access the dark excitons through spin-blockaded metastable biexcitons. D Andres-Penares et al [25] propose a versatile spectroscopic method that enables the identification of the out-of-plane component of dipoles due to the selective coupling of light emitted by in-plane and out-of-plane dipoles to the whispering gallery modes of spherical dielectric microresonators, in close contact to them.…”

Deterministic photon storage and readout in a semimagnetic quantum-dot--cavity system doped with a single Mn ion

“…Recent progress allows for indirectly accessing the dark exciton with light 31,32 or other complexes, 33 but alloptical control of the dark state using an intermediate biexciton state has also been proposed for the use as a long-lived qubit. 31,[34][35][36][37] Another possibility is the coupling of bright and dark states using micromechanical resonators, making the dark state addressable by light. 38 Still, it is much easier to excite the bright state.…”