Molecular Quantum Computing by an Optimal Control Algorithm for Unitary Transformations

Quantum computation is based on implementing selected unitary transformations which represent algorithms. A generalized optimal control theory is used to find the driving field that generates a prespecified unitary transformation. The approach is illustrated in the implementation of one and two qubits gates in model molecular systems.Comment: 10 pages, 2 figure

Long-lived quantum coherence in photosynthetic complexes at physiological temperature

Photosynthetic antenna complexes capture and concentrate solar radiation by transferring the excitation to the reaction center which stores energy from the photon in chemical bonds. This process occurs with near-perfect quantum efficiency. Recent experiments at cryogenic temperatures have revealed that coherent energy transfer - a wavelike transfer mechanism - occurs in many photosynthetic pigment-protein complexes (1-4). Using the Fenna-Matthews-Olson antenna complex (FMO) as a model system, theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature; these studies further show that this process is equivalent to a quantum random walk algorithm (5-8). This theory requires long-lived quantum coherence at room temperature, which never has been observed in FMO. Here we present the first evidence that quantum coherence survives in FMO at physiological temperature for at least 300 fs, long enough to perform a rudimentary quantum computational operation. This data proves that the wave-like energy transfer process discovered at 77 K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77 K and 277 K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations. The persistence of quantum coherence in a dynamic, disordered system under these conditions suggests a new biomimetic strategy for designing dedicated quantum computational devices that can operate at high temperature.Comment: PDF files, 15 pages, 3 figures (included in the PDF file

Optimizing sparse sampling for 2D electronic spectroscopy

We present a new data acquisition concept using optimized non-uniform sampling and compressed sensing reconstruction in order to substantially decrease the acquisition times in action-based multidimensional electronic spectroscopy. For this we acquire a regularly sampled reference data set at a fixed population time and use a genetic algorithm to optimize a reduced non-uniform sampling pattern. We then apply the optimal sampling for data acquisition at all other population times. Furthermore, we show how to transform two-dimensional (2D) spectra into a joint 4D time-frequency von Neumann representation. This leads to increased sparsity compared to the Fourier domain and to improved reconstruction. We demonstrate this approach by recovering transient dynamics in the 2D spectrum of a cresyl violet sample using just 25% of the originally sampled data points

Foundations for Cooperating with Control Noise in the Manipulation of Quantum Dynamics

This paper develops the theoretical foundations for the ability of a control field to cooperate with noise in the manipulation of quantum dynamics. The noise enters as run-to-run variations in the control amplitudes, phases and frequencies with the observation being an ensemble average over many runs as is commonly done in the laboratory. Weak field perturbation theory is developed to show that noise in the amplitude and frequency components of the control field can enhance the process of population transfer in a multilevel ladder system. The analytical results in this paper support the point that under suitable conditions an optimal field can cooperate with noise to improve the control outcome.Comment: submitted to Phys. Rev.

The Transition to IFRS and the Market Impact on European Banks

Die Arbeit untersucht die Auswirkungen der Umstellung auf Internationale Rechnungslegungsvorschriften bei europäischen Banken. Dabei werden verschiedene Aspekte bei der Untersuchung der Auswirkungen in den Vordergrund gestellt und die Umstellung aus verschiedenen Perspektiven beleuchtet

Nanoscale force manipulation in the vicinity of a metal nanostructure

The tight focus of Gaussian beams is commonly used to trap dielectric particles in optical tweezers. The corresponding field distribution generates a well-defined trapping potential that is only marginally controllable on a nanometre scale. Here we investigate the influence of a metal nanostructure that is located in the vicinity of the trapping focus on the trapping potential by calculating the corresponding field and force distributions. Even for an excitation wavelength that is tuned far from the plasmonic resonance of the nanostructure, the presence of the latter alters significantly the trap potential. For the given nanostructure, a ring of spheres that is illuminated in the axial direction, a smaller focus volume is observed in comparison to free focus. The superposition of this non-resonant Gaussian field with a planar wave illumination that is tuned to the plasmonic resonance gives a handle to modify the trapping potential. Polarization and intensity of the resonant illumination allows modifying the equilibrium position of the trapping potential, thus providing means to steer dielectric particles with nanometre precision. © 2007 IOP Publishing Ltd.TB thanks the DFG for an Emmy Noether Fellowship.Peer Reviewe