Periodic Reporting for period 1 - LiNQs (Lithium Niobate Quantum systems)
Berichtszeitraum: 2022-09-01 bis 2025-02-28
Quantum technologies are expected to have a transformative impact by exploiting fundamental quantum mechanical effects for technological applications such as quantum computation, quantum simulation, quantum communication, and quantum sensing. Photons are the only reliable qubit for quantum information transmission, making them an essential resource for quantum technologies. However, quantum photonics will only meet its expectation as a ground breaking technology when integrated in a scalable fashion. The solution lies in quantum photonic integrated circuits (QPICs) where photons are used to encode and process quantum information on-chip, offering scalable quantum information processing units. Currently, different integration platforms are investigated with a selection of building blocks available. However, no platform has shown a comprehensive toolbox combining all functionalities on a single chip. In this project we will demonstrate that the thin film lithium niobate on insulator platform can simultaneously link all quantum photonics building blocks on a single platform, resulting in fully integrated quantum photonic integrated circuits. We will develop integrated Lithium Niobate Quantum systems (LiNQs) showcasing the generation, manipulation, and analysis of photonic qubits. LiNQs develops a new nanofabrication and hybrid integration technology to link all photonic and optoelectronic building blocks on a single integration platform. LiNQs will engineer functional systems for future quantum technology applications, including long-range and on-chip quantum communication. The core of the projects lies in the optimization of individual photonic and optoelectronic components for system integration on a single platform. By developing all required building blocks and linking them to scalable systems, we will provide the quantum technology community a single integration platform for all quantum photonics applications. LiNQs will lay the foundation for Europe’s forefront position in a future photonics-driven quantum technology industry.
This project achieved significant progress in advancing quantum emitter integration within photonic circuits, focusing on precision control, localization, and the enhancement of quantum dot (QD) performance. One of our key breakthroughs was the successful demonstration of Rabi rotations in optically driven quantum dots under strong laser pulses. Improved sample quality and the stability of quantum dot-laser coupling enabled us to observe Rabi rotations despite phonon interactions—a finding that offers new insights into electron-phonon interactions. This understanding is pivotal, as it allows us to better tailor solid-state quantum emitters, which are foundational to various quantum technologies.
Another notable achievement was the development and characterization of quantum dots that emit in the telecom wavelength range by employing droplet etching techniques on InAlAs. This method yielded stable, strain-free quantum dots with emission at telecom wavelengths—an important advancement for fiber-compatible quantum communication systems. By precisely controlling the etching temperature, we achieved optimized dot geometry, resulting in highly symmetric, low-density nanoholes that enhance emission stability and efficiency.
To support high-quality photon generation, we further refined the cavity design to align with the biexciton-exciton transition in QDs, enhancing photon indistinguishability even in the absence of extreme Purcell enhancement. By carefully balancing cavity resonance and electron-phonon coupling, our optimized theoretical design achieved high entanglement and indistinguishability, crucial metrics for reliable quantum information applications, including entanglement swapping and other photon-based quantum protocols. Simulations validated that our optimized resonator is effective across realistic variations in structure, making this approach adaptable to different wavelengths, including the telecom band, which is crucial for fiber-based quantum communication.
Building on this, was the enhancement of single-photon emission through innovative cavity design. Embedding InAs QDs within Ag-clad GaAs nanopillars, we achieved Purcell-enhanced emission with impressive photon indistinguishability and minimal multi-photon emission. The low-Q cavity design allows for single-mode operation without requiring complex tuning mechanisms and has a wide bandwidth that can facilitate Purcell enhancement for transitions in high-temperature QDs. This feature makes the structure promising for room-temperature quantum applications and for exploring cooperative phenomena, such as superradiance, by coupling multiple QDs within a single cavity mode.
Furthermore, a method we developed for sub-10nm precision localization of quantum emitters during photoluminescence spectroscopy allowed us to seamlessly integrate QDs into cavities, which can subsequently be transferred onto photonic circuits. This localization capability, combined with our advanced pick-and-place technique for transferring devices, achieved placement accuracy below 50nm. This precision assembly approach enables the integration of diverse quantum photonic components onto platforms like lithium niobate on insulator (LNOI) circuits, thus paving the way for scalable, high-performance quantum photonic systems.
Overall, these accomplishments represent a significant leap forward in the integration, precision, and performance of quantum photonic devices, positioning this project at the forefront of developing scalable quantum technologies for applications in secure communication, quantum computing, and beyond.
Another notable achievement was the development and characterization of quantum dots that emit in the telecom wavelength range by employing droplet etching techniques on InAlAs. This method yielded stable, strain-free quantum dots with emission at telecom wavelengths—an important advancement for fiber-compatible quantum communication systems. By precisely controlling the etching temperature, we achieved optimized dot geometry, resulting in highly symmetric, low-density nanoholes that enhance emission stability and efficiency.
To support high-quality photon generation, we further refined the cavity design to align with the biexciton-exciton transition in QDs, enhancing photon indistinguishability even in the absence of extreme Purcell enhancement. By carefully balancing cavity resonance and electron-phonon coupling, our optimized theoretical design achieved high entanglement and indistinguishability, crucial metrics for reliable quantum information applications, including entanglement swapping and other photon-based quantum protocols. Simulations validated that our optimized resonator is effective across realistic variations in structure, making this approach adaptable to different wavelengths, including the telecom band, which is crucial for fiber-based quantum communication.
Building on this, was the enhancement of single-photon emission through innovative cavity design. Embedding InAs QDs within Ag-clad GaAs nanopillars, we achieved Purcell-enhanced emission with impressive photon indistinguishability and minimal multi-photon emission. The low-Q cavity design allows for single-mode operation without requiring complex tuning mechanisms and has a wide bandwidth that can facilitate Purcell enhancement for transitions in high-temperature QDs. This feature makes the structure promising for room-temperature quantum applications and for exploring cooperative phenomena, such as superradiance, by coupling multiple QDs within a single cavity mode.
Furthermore, a method we developed for sub-10nm precision localization of quantum emitters during photoluminescence spectroscopy allowed us to seamlessly integrate QDs into cavities, which can subsequently be transferred onto photonic circuits. This localization capability, combined with our advanced pick-and-place technique for transferring devices, achieved placement accuracy below 50nm. This precision assembly approach enables the integration of diverse quantum photonic components onto platforms like lithium niobate on insulator (LNOI) circuits, thus paving the way for scalable, high-performance quantum photonic systems.
Overall, these accomplishments represent a significant leap forward in the integration, precision, and performance of quantum photonic devices, positioning this project at the forefront of developing scalable quantum technologies for applications in secure communication, quantum computing, and beyond.
Two achievements stand out: droplet-etched quantum dots emitting at the telecom C-band, and new excitation techniques to coherently control quantum emitters. To fully realize the potential of these advancements, several steps are crucial. Continued research on emitter stability, brightness, and precise placement within complex photonic circuits will ensure higher efficiency and integration yield. Additionally, demonstration test-beds could further validate the reliability of these quantum emitters in real-world settings, providing a bridge to broader market applications. On a later stage after the project access to financial support for scaling up production and commercialization is essential, as are protective measures for intellectual property (IPR) to foster innovation while securing proprietary technology. Regulatory support for standardization in quantum photonics will also be key to ensuring consistent quality and interoperability across platforms and international standards.
In summary, the project hasalready produced a suite of innovations in quantum dot control, enhanced photon emission, and telecom-compatible quantum sources. These results lay the groundwork for future scalable quantum photonic devices, with wide-reaching applications in quantum computing, secure communications, and advanced photonic circuits.
In summary, the project hasalready produced a suite of innovations in quantum dot control, enhanced photon emission, and telecom-compatible quantum sources. These results lay the groundwork for future scalable quantum photonic devices, with wide-reaching applications in quantum computing, secure communications, and advanced photonic circuits.