In an article published in the journal Nature Communications, researchers proposed a platform for integrating tunable single photon emitters on large-scale photonic integrated circuits.
Study: Tunable Quantum Emitters on Photonic Circuits. Image Credit: asharkyu/Shutterstock.com
Photonic Integrated Circuit Platforms
Controlling large-scale many-body quantum systems at the single atomic system and single photon level is a key goal in quantum information science. Currently, developing systems to control many-quantum-dot quantum systems is a major challenge as this requires (i) scalable individual quantum dot control and (ii) low propagation loss-enabled efficiently mediated optical interactions.
These requirements can be addressed simultaneously by developing photonic integrated circuit platforms as on-chip solutions for quantum information processing. The successful deployment of these integrated quantum technologies critically depends on the compatibility of quantum dot structures with a specific photonic integrated circuit platform.
Although important approaches include monolithic III-V photonic integrated circuits, the requirement for specialized manufacturing and optical attenuation exceeding 15 dB/cm in III-V waveguides remain major limitations. Recent studies have focused on hybrid quantum emitter and photonic integrated circuit platform integration, including silicon nitride and silicon, to address the limitations.
However, these approaches did not combine (i) and (ii) with the advanced foundry-based silicon-on-insulator photonic integrated circuit platforms’ scaling advantages. Thus, the integration of atomic quantum systems with single-emitter tunability remains an open challenge.
The Proposed Approach
In this study, researchers proposed hybrid integration of multiple indium arsenide/indium phosphide (InAs/InP) microchiplets consisting of infrared high-brightness semiconductor quantum dot single photon emitters into advanced silicon-on-insulator photonic integrated circuits synthesized using a 300 mm foundry process to overcome the challenge of integrating atomic quantum systems with single-emitter tenability.
They tackled this challenge by achieving four significant breakthroughs simultaneously:
- Tuning the emission wavelength of individual single-photon emitters through the electronics of the photonic integrated circuit.
- Achieving resonance fluorescence from single-photon emitters that can be individually addressed.
- Employing scalable transfer printing techniques for the hybrid integration of multiple telecom quantum emitters.
- Implementing iterative manufacturing, design, and post-processing techniques for silicon-on-insulator photonic integrated circuits, achieving sub-3 dB fiber coupling efficiency in a 300 mm foundry.
The fabrication flow for the hybrid photonic integrated circuits started from the 2 × 5 mm2 photonic integrated circuit provided by the foundry, where metal and oxide layers covered the entire chip. Initially, researchers commenced the quantum socket fabrication from the circuit surface to the silicon waveguides.
They left a 100 nm oxide layer over the waveguides after optical lithography and wet etching to ensure good optical coupling and mechanical adhesion between the silicon-on-insulator photonic integrated circuit and the chiplet. The distance was determined by the position of an etch stop layer utilized in the quantum socket fabrication.
This etch stop was located 100 nm over the integrated circuit’s silicon layer, as determined by the foundry-used layer stack. Thinner oxide layers led to an improved optical coupling between silicon waveguides and the InP.
However, a smooth surface free of the doped electrode and patterned silicon waveguide-formed topography optimized the chipset transfer process. The foundry-specified default thickness of 100 nm was selected to ensure a consistent thickness of the oxide layer from one hybrid integration run to the next integration.
Simultaneously, researchers fabricated suspended InP chipsets with InAs/InP quantum dots embedded within them using electron beam lithography (EBL) and a combination of wet and dry etching. Subsequently, they transferred printed chipsets from the parent InP chip into the photonic integrated circuit quantum sockets.
This pick-and-place approach utilized an elastomer microstamp tracked under a microscope. Eventually, a 475 nm-thick PECVD oxide spacer layer was deposited, and a 20 nm chromium top electrode was patterned on the quantum socket.
Importance of this Work
This research demonstrated a significant advancement in quantum technology by achieving scalable emission wavelength tunability and programmability at the resolution of individual emitters. This was accomplished through the hybrid integration of InAs/InP chiplets with a silicon-on-insulator photonic integrated circuit. The integrated circuit's superior pump rejection capacity facilitated the observation of quantum dot resonance fluorescence without the need for additional filtering.
Moreover, the non-volatile localized spectral tuning introduced the possibility of adjusting quantum dot wavelengths across potentially millions of resolvable laser spots, achievable with standard microscopes. This capability opens up vast opportunities for precision applications in quantum computing and other technologies. However, the practical application of integrated quantum emitters is currently limited by their inherent spectral instability. Advances in charge stabilization techniques and innovative quantum dot growth methods show promise in overcoming these challenges.
In summary, this work not only achieved single-photon emission via resonance fluorescence and scalable emission wavelength tunability but also highlighted how integrating quantum and photonics systems on a scalable platform can lead to the development of programmable quantum information processors. These processors can be fabricated in major semiconductor foundries, harnessing the complex interactions of many-body quantum systems for enhanced functionality.
Journal Reference
Larocque, H. et al. (2024). Tunable quantum emitters on large-scale foundry silicon photonics. Nature Communications, 15(1), 1-9. DOI: 10.1038/s41467-024-50208-0, https://www.nature.com/articles/s41467-024-50208-0
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