Benedikt Fauseweh

Frequency modulated pulses for quantum bits coupled to time-dependent baths

p. By shaping the pulse, we perturbatively decouple the dynamics of the bath from the dynamics of the quantum bit during the pulse. Such shaped pulses provide single quantum bit gates robust against decoherence which are useful for quantum-information processing. We extend previous results in two ways: (i) we treat frequency modulated pulses and (ii) we pass from time-independent baths to analytically time-dependent baths. First- and second-order solutions for and = 2 pulses are presented. They are useful in experiments where amplitude modulation is dicult to realize.

Efficient algorithms for the dynamics of large and infinite classical central spin models

We investigate the time dependence of correlation functions in the central spin model, which describes the electron or hole spin confined in a quantum dot, interacting with a bath of nuclear spins forming the Overhauser field. For large baths, a classical description of the model yields quantitatively correct results. We develop and apply various algorithms in order to capture the long-time limit of the central spin for bath sizes from 1000 to infinitely many bath spins. Representing the Overhauser field in terms of orthogonal polynomials, we show that a carefully reduced set of differential equations is sufficient to compute the spin correlations of the full problem up to very long times, for instance up to

Magnetic excitations in the S = 1 2 antiferromagnetic-ferromagnetic chain compound BaCu 2 V 2 O 8 at zero and finite temperature

{10}^{5}\ensuremath{\hbar}/{J}_{\mathrm{Q}}

Multi-Particle Spectral Properties in the Transverse Field Ising Model by Continuous Unitary Transformations

where

Low-temperature thermodynamics of multiflavored hardcore bosons by the Brückner approach

{J}_{\mathrm{Q}}

Time-dependent correlations in quantum magnets at finite temperature

is the natural energy unit of the system. This technical progress renders an analysis of the model with experimentally relevant parameters possible. We benchmark the results of the algorithms with exact data for a small number of bath spins and we predict how the long-time correlations behave for different effective numbers of bath spins.

Anomalous behavior of control pulses in presence of noise with singular autocorrelation.

Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in

Finite-temperature line shapes of hard-core bosons in quantum magnets: A diagrammatic approach tested in one dimension

S=1/2

Quantum mechanical treatment of large spin baths

dimer magnets, as revealed by the unusual asymmetric lineshape of their excitations at finite temperatures. Here we quantitatively explore and parameterize the strongly correlated magnetic excitations at finite temperatures using the high resolution inelastic neutron scattering on the model compound BaCu

Nuclear frequency focusing in periodically pulsed semiconductor quantum dots described by infinite classical central spin models

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