Periodic Reporting for period 2 - QUDOT-TECH (Quantum Dots for Photonic Quantum Information Technologies)
Berichtszeitraum: 2022-01-01 bis 2024-06-30
We are presently on the verge of a second revolution of quantum science, where quantum engineering based on direct exploitation of fundamental quantum mechanical abilities such as superposition and entanglement promise entire new technologies for society. In QUDOT-TECH, we built from the semiconductor quantum dot - the most mature optical quantum information technology - and proposed a scalable platform for optical quantum information processing. Such a novel platform would pave the way for quantum technology to become a reality with benefits for society within health care, drug design, quantum chemistry, logistic optimization etc.
The main goal of the network was to produce the next generation of ESRs, trained to work across disciplinary and sectorial boundaries and therefore bring about step-changes in both research and technology development relating to optical quantum information processing.
The QUDOT-TECH network trained the ESRs to be capable of working at all technological maturity levels, from the basic research level to the mature application level with opportunities for industrial exploitation and commercialization. The network was organized in three scientific work packages, reflecting technological maturity levels from highly mature technologies (work package 1) adopted by spinout companies, to more applied research (work package 2) and to exploratory basic research (work package 3). Complemented by education in entrepreneurship and innovation, the team of ESRs contributed to moving Europe into a leading position in scientific and technological innovation within optical quantum technologies.
The main goal of the network was to produce the next generation of ESRs, trained to work across disciplinary and sectorial boundaries and therefore bring about step-changes in both research and technology development relating to optical quantum information processing.
The QUDOT-TECH network trained the ESRs to be capable of working at all technological maturity levels, from the basic research level to the mature application level with opportunities for industrial exploitation and commercialization. The network was organized in three scientific work packages, reflecting technological maturity levels from highly mature technologies (work package 1) adopted by spinout companies, to more applied research (work package 2) and to exploratory basic research (work package 3). Complemented by education in entrepreneurship and innovation, the team of ESRs contributed to moving Europe into a leading position in scientific and technological innovation within optical quantum technologies.
A main QUDOT-TECH activity was to train the ESRs scientifically, in communication and dissemination, as well as in exploitation and entrepreneurship. Scientific training took place in the form of local training, secondments and short visits, as well as in the form of Advanced Scientific Courses during the three summer schools. Similarly, transferable skills training took place predominantly during the Transferable Skills Modules at the summer schools.
Highlights of the scientific work carried out in the project included:
Sources with vertical emission: Tunability of the nano-trumpet single-photon source geometry was implemented at CEA combined with broadband Purcell enhancement. New designs allowing for improved collection from connected pillar structures was fabricated at C2N, and four-photon measurements was performed in collaboration with SAP. Furthermore, significant progress in single-photon source fiber-pig-tailing and integration in closed-cycle cryostat was achieved at QUA.
On-chip integration: A numerical simulation framework for analyzing and optimizing on-chip ridge waveguide single-photon source designs based on a FEM model was constructed at DTU in collaboration with JCM. Similarly, a model for analyzing V groove waveguide designs based on a FDTD model was established at DTU. Wafer-bonding technology was developed at DTU allowing for integration of quantum dots in a high-index GaAs/SiO2 platform. The superconducting properties of MoSi deposited on GaAs wafers for integration of on-chip detectors was investigated at BAS, and the results were well understood.
Spin-photon interfaces: An analytical and numerical framework based on a dedicated input-output formalism was established at NEEL. The framework took into account solid-state-induced decoherence, finite cooperativity and imperfect photon detection. New samples for use in spin-photon interface experiments were fabricated by C2N, where quantum non-demolition measurements were also realized between a single spin and coherent pulses of polarized light. Good progress in the control of the decoherence induced by the nuclear spin environment was achieved by CAM.
Phononic engineering: Phononic bandgaps at GHz frequencies resulting from phononic shield elements was numerically investigated at BAS. The resonators and acoustic shield elements were fabricated at NBI, and high quality factors were measured. Additionally, numerical simulations were carried out in order to assess the vibration modes of oscillating nanowires with different geometries at DTU. Furthermore, nanowire-quantum dot geometries fulfilling all requirements for performing quantum non-demolition measurements were identified.
Highlights of the scientific work carried out in the project included:
Sources with vertical emission: Tunability of the nano-trumpet single-photon source geometry was implemented at CEA combined with broadband Purcell enhancement. New designs allowing for improved collection from connected pillar structures was fabricated at C2N, and four-photon measurements was performed in collaboration with SAP. Furthermore, significant progress in single-photon source fiber-pig-tailing and integration in closed-cycle cryostat was achieved at QUA.
On-chip integration: A numerical simulation framework for analyzing and optimizing on-chip ridge waveguide single-photon source designs based on a FEM model was constructed at DTU in collaboration with JCM. Similarly, a model for analyzing V groove waveguide designs based on a FDTD model was established at DTU. Wafer-bonding technology was developed at DTU allowing for integration of quantum dots in a high-index GaAs/SiO2 platform. The superconducting properties of MoSi deposited on GaAs wafers for integration of on-chip detectors was investigated at BAS, and the results were well understood.
Spin-photon interfaces: An analytical and numerical framework based on a dedicated input-output formalism was established at NEEL. The framework took into account solid-state-induced decoherence, finite cooperativity and imperfect photon detection. New samples for use in spin-photon interface experiments were fabricated by C2N, where quantum non-demolition measurements were also realized between a single spin and coherent pulses of polarized light. Good progress in the control of the decoherence induced by the nuclear spin environment was achieved by CAM.
Phononic engineering: Phononic bandgaps at GHz frequencies resulting from phononic shield elements was numerically investigated at BAS. The resonators and acoustic shield elements were fabricated at NBI, and high quality factors were measured. Additionally, numerical simulations were carried out in order to assess the vibration modes of oscillating nanowires with different geometries at DTU. Furthermore, nanowire-quantum dot geometries fulfilling all requirements for performing quantum non-demolition measurements were identified.
In spite of the numerous delays in project activities due to the corona pandemic, the project output included: A nanopost single-photon source geometry with a measured extraction efficiency of 0.35 and a broadband Purcell enhancement of 5 was demonstrated in a joint effort led by CEA. A study on molecular beam epitaxy grown quantum dots with a contaminated aluminum evaporation cell was conducted by RUB and a way of addressing this problem to restore growth of excellent low noise heterostructures was identified. Optical driving of the radiative Auger transition in a trion of a semiconductor quantum dot was demonstrated linking few-body Coulomb interactions and quantum optics.
The project aimed at continuously producing and communicating progress results within optical quantum-dot based quantum technology, both to the scientific community and the wider audience. In particular, we achieved our project objectives of demonstrating the scalability of optical quantum information technology, through the demonstrations of unprecedented SPS and entangled-photon pair brightness, on-chip integration capability and optical gating with full control of the decoherence. As a highlight, new micropillar single-photon source structures with improved first lens brightness were obtained, with a measured record value of 55% efficiency. The sources were later used for the first quantum computing prototype demonstrations at QUA with 6 photons. While the scientific work performed remains of a fundamental research character and was severely impacted by the corona crisis, the output results have been published in prestigious journals including Nature Photonics, Nature Nanotechnology, and Nature Communications, Physical Review Letters, Nano Letters and ACS Photonics, and selected work was presented at international conferences including Quantum Information and Measurement VI, SPIE, CLEO and the APS.
The project aimed at continuously producing and communicating progress results within optical quantum-dot based quantum technology, both to the scientific community and the wider audience. In particular, we achieved our project objectives of demonstrating the scalability of optical quantum information technology, through the demonstrations of unprecedented SPS and entangled-photon pair brightness, on-chip integration capability and optical gating with full control of the decoherence. As a highlight, new micropillar single-photon source structures with improved first lens brightness were obtained, with a measured record value of 55% efficiency. The sources were later used for the first quantum computing prototype demonstrations at QUA with 6 photons. While the scientific work performed remains of a fundamental research character and was severely impacted by the corona crisis, the output results have been published in prestigious journals including Nature Photonics, Nature Nanotechnology, and Nature Communications, Physical Review Letters, Nano Letters and ACS Photonics, and selected work was presented at international conferences including Quantum Information and Measurement VI, SPIE, CLEO and the APS.