Fault-tolerant superconducting qubits

• Applicant: Professor Dr. Yuriy Makhlin
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2003 to 2008
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5406116

We plan to adopt and extend certain concepts of error correction which originally had been developed for quantum optical systems to quantum information devices based on Josephson-junction technologies. One of the interesting ideas of error correction is the concept of continuous-variable codes in systems with continuous quantum degrees of freedom, which was proposed by Gottesman et al. These authors described how, in principle, the necessary steps can be performed with quantum optical systems. We observe that the needed steps, in particular the preparation of the logic basis states, can be performed in an efficient and precise way using hard-ware properties of Josephson-junction devices. In view of the spectacular results obtained with Josephson-junction based quantum systems in the last year (with phase coherence times demonstrated to exceed 1 µsec as compared to less than 100 psec single-bit operation times) we can expect further progress in the near future. In particuar efforts are made to demonstrate logic operations with multi-qubit systems. The purpose of the proposed project is to describe theoretically the mentioned error correction steps for different designs of Josephson devices (charge, flux, or phase regime) as well as different measurement devices (SET, SQUID, or resonant activation) and to analyze questions of phase coherence which arise in these contexts.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1078: Quanten-Informationsverarbeitung
• Participating Person: Professor Dr. Gerd Schön