Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission (1503.07141v2)

Abstract: Self-assembled, epitaxially-grown InAs/GaAs quantum dots are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of quantum dots, presenting a challenge in creating devices that exploit the strong interaction of single quantum dots with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single quantum dots with respect to alignment features with an average position uncertainty < 30 nm (< 10 nm when using a solid immersion lens), which represents an enabling technology for the creation of optimized single quantum dot devices. To that end, we create quantum dot single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48 % +/- 5 % into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50 %), low multiphoton probability (g(2)(0) <1 %), and a significant Purcell enhancement factor (~ 3).

• The paper introduces a photoluminescence imaging method that maps individual InAs/GaAs quantum dots with under 10 nm uncertainty using a solid immersion lens.
• The paper demonstrates integration of circular Bragg grating devices achieving 48% light collection, a Purcell factor of ~3, and low multiphoton probability (g²(0) < 1%).
• The paper’s advancements enable precise QD-cavity coupling that minimizes tuning constraints and paves the way for scalable quantum photonic technologies.

Nanoscale Optical Positioning of Single Quantum Dots for Bright and Pure Single-Photon Emission

This paper presents a significant advancement in the integration of single quantum dots (QDs) for photonic quantum information technologies, focusing on their precise optical positioning for optimized single-photon emission. The paper centers on InAs/GaAs quantum dots due to their potential in solid-state quantum emitters applications. Acknowledging the limitations posed by the random in-plane distribution characteristic of self-assembled QDs, the authors develop a photoluminescence imaging methodology capable of mapping the spatial positions of individual quantum dots with uncertainties less than 30 nm, further refined to less than 10 nm when enhanced by a solid immersion lens. This precision is crucial for optimizing interactions with highly confined optical modes.

The team reports the construction of QD single-photon sources employing a circular Bragg grating (CBG) design, achieving high-efficiency light collection (48% ± 5% into a numerical aperture of 0.4), low multiphoton probability (g^2(0) < 1%), and a Purcell enhancement factor of approximately 3. These results mirror the predicted theoretical efficiencies closely and represent an advancement in producing efficient QD devices.

To achieve these results, the authors elaborated on their process for accurate positioning:

1. Photoluminescence Imaging: A two-color imaging process detects QD positions relative to fiducial alignment marks, allowing for a single image determination with sub-50 nm accuracy, enhanced by a solid immersion lens for increased photon collection.
2. Spectral Characterization: The emission wavelength and polarization of individual QDs were determined using a 780 nm laser excitation, facilitating precise tailoring of the subsequent nanophotonic structures formed around these QDs.
3. Fabrication: The CBG devices, calibrated to resonate with specific QDs, were fabricated on the GaAs substrate. The calibration correlates the experimental cavity resonances with the aims of matching specific QD wavelengths.

The implications of the research are twofold, impacting both theoretical and practical dimensions. The paper not only enhances the understanding and control over QDs for efficient single-photon creation but also sets a precedent for integrated photonic devices where exact emitter positioning is vital. This positioning capability allows devices with minimized detuning needs, reducing tuning constraints on device scalability.

Looking forward, the paper invites further exploration into improving the QD-cavity coupling using other schemes, such as fine-tuned resonators for enhancing indistinguishability and fidelity of emitted photons necessary for quantum information applications. The methods utilized underscore the merging of nanotechnology with quantum optics for developing next-generation quantum devices.

In conclusion, the research contributes substantially to the field by presenting a method for precise QD positioning relative to integrated photonic devices, overcoming key challenges in photonic circuit integration and quantum efficiency. This work illustrates a balance between device engineering and quantum photonic science, paving the way for practical and scalable applications in the burgeoning field of quantum technologies.