QUROPE Quantum Information Processing and Communication in Europe

C. F. Roos (P4a OEAW), seminar, Quantenmessungen mit Ionenkristallen

C. F. Roos (P4a OEAW), seminar, Quantum simulations with trapped ions: analog vs digital

C. F. Roos (P4a OEAW), Quantum Information processing with trapped ions

R. Blatt (P4a OEAW), invited lecture, New Trends in Quantum Matter with Cold Atoms and Molecules, April 5, 2011

R. Blatt (P4a OEAW), talk,  Quantum Information Science with Trapped Ions

C. F. Roos (P4a OEAW), talk, Towards quantum simulations with trapped ions

F. Schimdt-Kaler (P18 JGUM), invited talk, Modern ion traps in 3D and 2D geometry and spin-spin interactions in cold ion crystals

S. Montangero (P1 UULM), invited talk, Control of Many Body Quantum Systems

M. Lewenstein (P7 ICFO), invited speaker

G. Morigi (P8 USAAR), invited talk, Entangling two distant oscillators with a quantum reservoir

R. Blatt (P4a OEAW), invited lecture, New Trends in Quantum Matter with Cold Atoms and Molecules, April 4, 2011

R. Blatt (P4a OEAW), talk, Status of TRapped-Ion Physics in Europe

R. Blatt (P4a OEAW), invited talk, Quantum Information Processing and Quantum Simulations with Trapped Ca+ Ions

J.I. Cirac (P3c MPQ), invited talk, Engineered dissipation and quantum information

P. Treutlein (P19 UNIBAS), invited talk, Quantum metrology with ultracold atoms on a chip

B. Michuck (P9 UAARHUS), poster

J. Gulliksen (P9 UAARHUS), attendance

F. Schmidt-Kaler (P18 JGUM), contribution, Rydberg Excitation with trapped cold ions

We report the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.

The computational potential of a quantum processor can only be unleashed if errors during a quantum computation can be controlled and corrected for. Quantum error correction works if imperfections of quantum gate operations and measurements are below a certain threshold and corrections can be applied repeatedly. We implement multiple quantum error correction cycles for phase-flip errors on qubits encoded with trapped ions. Errors are corrected by a quantum-feedback algorithm using high-fidelity gate operations and a reset technique for the auxiliary qubits.