Final Report Summary - QUANTUMWALKS (Quantum walks in superconducting networks)
The project, Quantum Walks in Superconducting Networks, is to design and implement a Boson Sampling system in a superconducting Josephson device platform. The achievement of such a system will ultimately allow us to implement a post-classical computational power system without the full complexity and technical overhead of quantum computing error correction. The basic framework is that of non-interacting microwave excitations ("Bosons" or "Photons") hopping via the coupling between resonators on a superconducting chip. The excitations are fed into the coupled array of resonators via superconducting qubits ("transmons") which also serve as the measurement of the occupation after the excitations are allowed to diffuse coherently in the array. We have developed the infrastructure to achieve this goal, including the physics of coupled resonator arrays, measurement and amplification of single microwave photons and the study of interaction and loss non-linearities. We have determined how to use active feedback and quantum error correction to establish a high sensitivity measurement, beyond the standard quantum limitations of qubit lifetime (theory project) We have achieved large coupled arrays of resonators, with long lifetimes (over 10 microseconds is typically achieved). We have also successfully measured nonlinearities and couplings with exquisite precision for a two-resonator coupled system, which helps us establish the know-how to scale up to larger coupled arrays. We have fabricated and tested a fully integrated chip with a resonator array (6 modes), fed and read-out by individual qubits.