Abstract
The capability to embed self-assembled quantum dots (QDs) at predefined positions in nanophotonic structures is key to the development of complex quantum photonic architectures. Here, we demonstrate that QDs can be deterministically positioned in nanophotonic waveguides by pre-locating QDs relative to a global reference frame using micro-photoluminescence ($\mu$PL) spectroscopy. After nanofabrication, $\mu$PL images reveal misalignments between the central axis of the waveguide and the embedded QD of only $(9\pm46$) nm and $(1\pm33$) nm, for QDs embedded in undoped and doped membranes, respectively. A priori knowledge of the QD positions allows us to study the spectral changes introduced by nanofabrication. We record average spectral shifts ranging from 0.1 to 1.1 nm, indicating that the fabrication-induced shifts can generally be compensated by electrical or thermal tuning of the QDs. Finally, we quantify the effects of the nanofabrication on the polarizability, the permanent dipole moment and the emission frequency at vanishing electric field of different QD charge states, finding that these changes are constant down to QD-surface separations of only 70 nm. Consequently, our approach deterministically integrates QDs into nanophotonic waveguides whose light-fields contain nanoscale structure and whose group index varies at the nanometer level.
Highlights
Assuming that our field of view is unchanged between these two images, we find the position of each quantum dots (QDs) relative to the global reference frame with an accuracy δ = 4.9 nm that is dominated by the uncertainty in the cross position
We have presented a method for precisely locating epitaxially grown QDs that allows us to deterministically integrate the emitters into nanostructured photonic waveguides
In contrast to previous approaches, we only rely on photoluminescence data and not on reflections to image both the QDs and a global reference frame
Summary
The rapid maturation of the InAs self-assembled quantum dot (QD) platform, and in particular, the ability to interface these emitters with high-quality nanophotonic structures,[1] has opened up viable routes toward the creation of integrated single-photon sources[2] for quantum network applications.[3,4] This increasing viability of QD-based photonic technology can be traced to three milestones in the field: the growth of high-quality QDs via the Stranski– Krastanov technique,[5] the ability to couple emission from QDs to photonic modes with near-unity efficiency,[6,7] and the use of doped heterostructures to charge stabilize the environment of the emitters.[8,9] Altogether, these allow for efficient and highly coherent light– matter interactions[9–11] and the generation of highly indistinguishable photons,[12,13] which are basic capabilities of quantum-photonic processing elements. The rapid maturation of the InAs self-assembled quantum dot (QD) platform, and in particular, the ability to interface these emitters with high-quality nanophotonic structures,[1] has opened up viable routes toward the creation of integrated single-photon sources[2] for quantum network applications.[3,4] This increasing viability of QD-based photonic technology can be traced to three milestones in the field: the growth of high-quality QDs via the Stranski– Krastanov technique,[5] the ability to couple emission from QDs to photonic modes with near-unity efficiency,[6,7] and the use of doped heterostructures to charge stabilize the environment of the emitters.[8,9]. In the case of photonic-crystal cavities in a strong coupling regime,[22,23] final QD-nanostructure misalignment of the order of Δ ≈ 50 nm has been determined by comparing the measured coupling constant with the maximum calculated value. We study the effect of fabricating quasi-one-dimensional nanophotonic waveguides or two-dimensional photonic-crystal waveguides (PhCWs) on the spectral response of the QDs and on the different exciton complexes
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