By the end of Period 1 (Year 1), the QRC-4-ESP project had made the following progress
WP1 – QR Theory and Models
• A first-principles quantitative model of a set of transmon qubits in a waveguide is developed and successfully tested on the experimental data from WP2.
• A generic model of a qubit-based quantum reservoir developed and used to simulate different regimes of quantum reservoir operation.
• A new approach to quantum reservoir operation (“measurevoir”) proposed.
• A quantitative model of a defect-based qubit developed.
WP2 – Superconducting QR
• Designed, fabricated and tested a sample containing 5 superconducting qubits coupled to coplanar waveguide resonator.
• Determined the dependence transmission coefficient on the applied power and magnetic field.
• Observed bistability, explained by the theory of WP1.
WP3 – Defect-based QR
• Designed a quantum system consisting of one to several Si vacancies in 4H-SiC with electron spin S=3/2. Each Si vacancy has a quartet spin state in both the ground and excited state, |±1/2> and |±3/2>, which can be optically readout by photoluminescence excitation (PLE).
• Realised isolated Si vacancy emitters and clusters of several Si vacancies by electron irradiation in 15 pure 4H-SiC samples. Photoluminescence (PL) mapping using confocal microscope allows to determine the density of emitters for choosing and optimising quantum systems for optically detected magnetic resonance (ODMR) and PLE studies.
• Used isotope-pure layers to reduce the magnetic noises from the nuclear spin bath (13C and 29Si isotopes), the pure layers help to reduce both the decoherence caused by dipole interaction of other defects and impurities and the electric noise from local environment induced by ionisation of other defects under optical excitation. Made hundreds of PLE scans continuously under resonant excitation without repump laser that showed stable single Si emitters without signs of ionisation.
• Demonstrated that single Si vacancies within quantum system nonlinearly interact with each other, with spins of other defects and the nuclear spin bath via dipole-dipole interaction and with charges in the local environment, which induce changes in PLE spectra. Potential inputs can be the laser power, the external magnetic field, and the microwave (MW) power, and outputs are the energy shift of the zero-phonon lines (ZPL) corresponding to optical transitions between |±1/2> (A1 line) states and between |±3/2> (A2 line), and their intensities. These parameters have been accounted for in theoretical models as perturbations.
• Collected PLE data for some clusters with different sizes. The obtained PLE data confirm that the model of Si vacancy quantum system is working in principle.
WP4 – QRC Integration, Demonstration and Benchmarking
• Implemented effective input/output strategies for Quantum Reservoir Computing (QRC) systems integrated with neural networks. Successfully tested a Python-based simulator for data encoding and extraction, validating the linear readout mechanism for regression and classification tasks.
• Designed a benchmark suite to evaluate QRC systems' performance on tasks like regression, classification, time-series forecasting, clustering, and anomaly detection using synthetic datasets. Performance metrics (MSE, NMSE) are used to systematically assess QR-enhanced and traditional networks.
• Initiated benchmarking of experimental QRC systems for industrial tasks like signal processing and anomaly detection, with plans for future integration of refined prototypes and real-world applications.
WP5 – Dissemination, Communication and Exploitation
• Presented scientific results via 10 papers and posters at international conferences.
• Published a short-animation explanatory video about the QRC-4-ESP project.
• Published 20 separate news announcements via the project website and social media accounts.
• Participated in numerous outreach events (Pint of Science, online brokerage and showcase events).
