Superconducting quantum computers
The SQUBIT European collaboration is examining the feasibility of quantum information processors using Josephson junction nanotechnology at low, superconducting temperatures. The ultimate aim of the project is to create an exclusive XOR gate thus opening the way to quantum computing. Superconducting technologies have a unique potential for realizing compact solid state devices with controllable macroscopic quantum properties and long coherence time. Superconducting technologies represent the most realistic approach for a technology for quantum computers. Experiments with Josephson junction circuits demonstrated long-lived coherent oscillations, stressing the need for a theory analysis of the dissipative dynamics of qubits subject to noise sources. Such noise sources may rise from background charge fluctuations or variations of critical currents and magnetic fields. The project group has studied extensively the influence of various noise sources on the dynamics of two level systems at optimal points and their analysis has been published in well-known physics journals. Another obstacle in applying quantum information technology is the lack until now of a reliable quantum detector. A real physical system that can efficiently read out the final state of a qubit. A weakly coupled detector may perform a single shot measurement only if it measures an observable that is conserved. In quantum mechanics, an observable is conserved only if it commutes with the Hamiltonian of the system, like energy, and the detector then works in the quantum-non-demolition (QND) regime. The research group focused on continuous weak non-QND measurements of the coherent oscillations of a qubit. The study of the output spectrum of a measuring device at arbitrary voltage and temperature has also been published in well-known physics journals.
