Master's thesis presentation, Veronika Beliaeva EMNAN

Student: Veronika Beliaeva, EMNAN
Examiner: Simone Gasparinetti
Supervisor: Axel Eriksson

Abstract:
Bosonic quantum computing utilizes the high dimensionality of harmonic oscillators to encode and manipulate quantum information. Superconducting planar circuits offer a promising platform for creating quantum computing chips, enabling universal control over individual bosonic modes via ancillary superconducting qubits. To achieve universal control in a multi-mode system, the extension of control through two-mode gates is sufficient. An example of a two-mode gate is a beamsplitter, which is a natural and easily achievable element in superconducting circuits. The physical realization of this gate involves connecting microwave resonators through a nonlinear coupler. In this project, we designed a planar superconducting platform hosting four individual modes, each coupled to a SNAIL-based single coupler, leading to a fully connected system. Fine-tuning the SNAIL coupler’s potential allows in-situ cancellation of the unwanted nonlinear Kerr interactions, making it a suitable connectivity element. After the fabrication of the designed chip, we experimentally characterize its parameters and demonstrate beamsplitting through parametric flux modulation. To visualize and validate the experimental results, we employed Wigner tomography on one of the cavities' quantum state. The SNAIL-based intercavity beamsplitter interaction could potentially open new pathways for two-mode gate mechanisms by simultaneously beamsplitting pairs of modes in a highly interconnected system.