Principal Investigator: Professor Christof Wunderlich

The Project

Quantum simulation

One way to overcome difficulties associated with universal quantum computing is to use one quantum system to simulate the dynamics of another quantum system. This general idea was originally conceived by R. Feynman. Recently, concrete proposals for quantum simulations have been made using a chain of pairwise coupled spins described by a Heisenberg model or a variant thereof. Such models serve as a starting point for numerous theoretical investigations in various branches of Physics, and in particular in Condensed-Matter Physics where collective effects, like [anti-] ferromagnetism and superconductivity, are investigated. To date, experimental quantum simulations have only just started to emerge and have been realized using only few qubits.

A spin chain made up of individual electrodynamically trapped ions shall be developed with the ability to coherently manipulate and read-out individual members of this many body system. Furthermore, the spin-spin coupling strength and range of interaction shall be controllable by the experimenter [4,5] A novel type of ion trap will be developed, designed, and constructed that includes magnetic field generating elements as an integral part inducing the desired spin-spin coupling. Linear chains of Yb+ ions will be trapped and individual spins addressed in frequency space using microwave radiation or rf radiation, and adjustable spin-spin coupling will be demonstrated. Entangled states relying on theoretical concepts developed in WP4.3 and WP4.7 shall be generated and analyzed. 
 

Quantum control

In order to physically implement universal quantum computation and apply it to interesting problems, quantum gates have to be executed with demandingly high precision and need to be applied to a large numbers of qubits. A way to cope with the daunting requirements of universal quantum computing is the development of practical schemes for better control of the quantum evolution of individual building blocks for quantum information processing, that is, error correction, characterization and subsequent control of decoherence, and of robust and optimized quantum gates. A collaboration with TU Munich already lead to the implementation of quantum gates based on optimal control theory, that are insensitive to variations in experimental control parameters and intrinsically unknown system parameters [1].


Subproject management

Regular meetings or workshops are organised. Such meetings across the entire sub-project are intended to enable coordination of the research effort and to manage the realization of deliverables, as well as raise awareness of the facilities and expertise of the different partners and identify opportunities for collaboration.


Other QAP Activities
• State and Process Estimation (with IPSAS)
• Quantum gates with NV centres (with USTUTT)

List of Publications

QAP

[1] N. Timoney, V. Elman, S. Glaser, C. Weiss, M. Johanning, W. Neuhauser, Chr. Wunderlich, Error-resistant Single Qubit Gates with Trapped Ions, submitted to Phys. Rev. Lett. quant-ph/0612106

[2] M. Pons, V. Ahufinger, Chr. Wunderlich, A. Sanpera, S. Braungardt, A. Sen(De), U. Sen, M. Lewenstein, Trapped Ion Chain as a Neural Network: Error-Resistant Quantum Computation, Physical Review Letters 98, 023003 (2006), quant-ph/0607016

[3] Alexander Braun, PhD thesis, University of Siegen, 2007

A. Braun, Chr. Paape, Chr. Balzer et al, Resonance enhanced isotope-selective photoionization of YbI for ion trap loading, submitted to Appl. Phys. B arXiv:0712.0969

M. Johanning, A. Braun, N. Timoney et al, Individual addressing of trapped ions and coupling of motional and spin states using rf radiation, submitted to Nature Phys. arXiv:0801.0078


Related work

[4] F. Mintert and Ch. Wunderlich, Ion trap quantum logic using long wavelength radiation, Physical Review Letters 87, 257904 (2001); Ch. Wunderlich, Conditional spin resonance with trapped ions, Laser Physics at the Limit, Springer Verlag, Heidelberg-Berlin-New York, 2002, pp 261-271; Ch. Wunderlich, Ch. Balzer (2003), Quantum measurements and new concepts for experiments with trapped ions, Advances in Atomic, Molecular, and Optical Physics Vol. 49, Academic Press, 2003, pp 295-376.

[5] D. Mc Hugh and J. Twamley, Phys. Rev. A 71, 012315 (2005)

[6] Chr. Balzer, A. Braun, T. Hannemann, Chr. Paape, M. Ettler, W. Neuhauser, and Chr. Wunderlich: Electrodynamically trapped Yb+ ions for quantum information processing, Physical Review A 73, 041407(Rapid Comm.) 2006. quant-ph/0602044

[7] Chr. Wunderlich, Th. Hannemann, T. Koerber et al, Robust state preparation of a single trapped ion by adiabatic passage, accepted for publication in J. Mod. Opt.

M. Pons, V. Ahufinger, C. Wunderlich et al, Trapped Ion Chain as a Neural Network: Error-Resistant Quantum Computation, accepted for publication in Phys. Rev. Lett. quant-ph/0607016

Chr. Wunderlich, Th. Hannemann, T. Koerber et al, Robust state preparation of a single trapped ion by adiabatic passage, accepted for publication in J. Mod. Opt.