Highly indistinguishable photons from deterministic quantum-dot microlenses utilizing three-dimensional in situ electron-beam lithography

Abstract

The success of advanced quantum communication relies crucially on non-classical light sources emitting single indistinguishable photons at high flux rates and purity. We report on deterministically fabricated microlenses with single quantum dots inside which fulfil these requirements in a flexible and robust quantum device approach. In our concept we combine cathodoluminescence spectroscopy with advanced in situ three-dimensional electron-beam lithography at cryogenic temperatures to pattern monolithic microlenses precisely aligned to pre-selected single quantum dots above a distributed Bragg reflector. We demonstrate that the resulting deterministic quantum-dot microlenses enhance the photon-extraction efficiency to (23±3)%. Furthermore we prove that such microlenses assure close to pure emission of triggered single photons with a high degree of photon indistinguishability up to (80±7)% at saturation. As a unique feature, both single-photon purity and photon indistinguishability are preserved at high excitation power and pulsed excitation, even above saturation of the quantum emitter.

Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

“…To develop these non-classical light sources, the nanophotonics of semiconductor quantum dots (QDs) [7][8][9] has been a field under intense scientific investigation. Although ultrapure and highly indistinguishable single-photon generation has been achieved in various arsenide-based QD systems [10][11][12][13][14], the large band offsets and strong exciton binding energies of III-nitride materials are needed for the realization of polarized photon emission [15][16][17] and room temperature operation [18,19]. These polarized single-photon sources can then fulfill the need for on-chip polarization encoding in quantum cryptography, such as the BB84 protocol [20].…”

Bright Single-Photon Sources Based on Anti-Reflection Coated Deterministic Quantum Dot Microlenses

“…Taking the PEE of 25%-29% found for uncoated microlenses with backside DBR in Refs. [18,19] using a microscope objective with NA of 0.4 and multiplying it with the integrated intensity ratio from above, we predict a PEE of up to 50% for the AR-coated microlenses with DBR. This enhancement of PEE clearly highlights the benefits of suitable AR-coatings for QD-based single-photon sources that normally suffer from Fresnel-reflections at the semiconductor-vacuum interface.…”

“…It includes a lower mirror based on a distributed Bragg reflector (DBR) consisting of 23 alternating λ/4-thick layers of AlGaAs (77.0 nm) and GaAs (65.7 nm). The DBR is followed by a GaAs spacer (65.0 nm), a low-density layer of Stranski-Krastanov self-assembled InGaAs-QDs, and a 400 nm thick GaAs capping layer [19]. This layout allows for the collection of QD-photons emitted into the lower hemisphere, thereby boosting the PEE of microlenses further.…”

“…Our device concept is based on monolithic microlenses precisely aligned (with 24 nm accuracy [17]) to pre-registered single QDs, allowing for an increased PEE of single photons of up to 29% [18] and close to ideal quantum optical properties in terms of the multiphoton suppression and the photon indistinguishability [19]. An important advantage of the microlens concept is the broadband enhancement of the PEE (a bandwidth of~50 nm has been calculated via finite-element method (FEM) simulations).…”

Сверхминиатюрные излучатели на основе одиночной (111) In(Ga)As квантовой точки и гибридного микрорезонатора

“…Формирование микролинзовых структур производи-лось с использованием установки, созданной на базе электронного микроскопа JEOL JSM 840, на которой проводилось измерение спектров криогенной КЛ ис-ходной структуры, и после определения латеральных координат одиночных КТ проводились 3D электронная литография и формирование линзоподобных резистив-ных масок, расположенных над одиночными КТ [21]. На рис.…”