Deliverable D1.1 — Report on scalable qudit characterization techniques, error model, and certification of the quantum performance
This report outlines the developments within NeQST towards scalable qudit characterization techniques, error model, and certification of the quantum performance. Compared to their simpler two-level counterpart, qudits present a range of new challenges due to the richer Hilbert space structure.
Characterization techniques must be carefully designed to avoid unnecessary overheads. Here, scalable techniques were developed that exploit inherent correlations between calibration parameters and use continuous compensation rather than tedious characterization. This enables the compensation of unwanted phase shifts, a primary challenge in qudits, with minimal calibration overhead.
Noise models become more involved than for qubits, where phenomenological depolarizing noise goes a long way. In trapped ion systems, however, noise is generally driven by gate operations. As a consequence, noise in qudit systems, where gates generally act on subspaces, is not well described by depolarizing noise. While microscopic noise modelling accurately describes the qudit gates, this is impractical for circuit simulations pursued within NeQST. Hence, we developed a phenomenological noise model that is easy to handle in classical simulations and closely approximates the system performance.
Finally, the development of software phase gates enables software phase tracking for entangling gates, as well as optimized pulse sequences. The latter is demonstrated to reduce the gate count and thereby increase the fidelity of local operations by over a factor of 2.
Deliverable D1.1 — Report on scalable qudit characterization