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- Wirtschaft und Informationstechnik Bocholt (68) (entfernen)
Dephasing in quantum systems is typically the result of their interaction with environmental degrees of freedom. We investigate within a spin-boson model the influence of a super-Ohmic environment on the dynamics of a quantum two-state system. A super-Ohmic environment thereby models typical bulk phonons which are a common disturbance for solid state quantum systems as, for example, nitrogen-vacancy centers. By applying the numerically exact quasiadiabatic path-integral approach we show that for strong system-bath coupling, pseudocoherent dynamics emerges, i.e., oscillatory dynamics at short times due to slaving of the quantum system to the bath dynamics. We extend the phase diagram known for sub-Ohmic and Ohmic environments into the super-Ohmic regime and observe a pronounced nonmonotonous behavior. Super-Ohmic purely dephasing fluctuations strongly suppress the amplitude of coherent dynamics at very short times with no subsequent further decay at later times. Nevertheless, they render the dynamics overdamped. The corresponding phase separation line shows also a nonmonotonous behavior, very similar to the pseudocoherent dynamics.
We study a quantum two-level system under the influence of two independent baths, i.e., a sub-Ohmic pure dephasing bath and an Ohmic or sub-Ohmic relaxational bath. We show that cooling such a system invariably polarizes one of the two baths. A polarized relaxational bath creates an effective asymmetry. This asymmetry can be suppressed by additional dephasing noise. This being less effective, the more dominant low frequencies are in the dephasing noise. A polarized dephasing bath generates a large shift in the coherent oscillation frequency of the two-level system. This frequency shift is little affected by additional relaxational noise nor by the frequency distribution of the dephasing noise itself. As our model reflects a typical situation for superconducting phase qubits, our findings can help optimize cooling protocols for future quantum electronic devices.
Die Erosion des Normalunternehmertums als Cance für eine notwendige Entrepreneurial Diversity
(2007)
Die Autorinnen stellen erste Ergebnisse aus ihrem Forschungsprojekt 'Vielfalt in der Unternehmerschaft: Facetten des Unternehmerinnenbildes in Deutschland' vor, in welchem u.a. folgende Fragen untersucht werden: Welches Selbstbild entwickeln Frauen zwischen dem Entschluss, unternehmerisch tätig zu werden, bis zur Gründung, Übernahme oder Weiterführung eines Unternehmens? Welche Rolle spielen hierbei staatliche Programme, aber auch Leitbilder aus der Personalentwicklung oder von beratenden Institutionen, Organisationen sowie Expertinnen bzw. Experten? Ab welchem Zeitpunkt verstehen Frauen sich selbst als erfolgreiche Unternehmerinnen und wie werden sie von anderen an diesen Prozessen beteiligten Akteuren gesehen? Es wurde folgende Arbeitshypothese zugrunde gelegt: Ein hegemoniales und einseitig männlich geprägtes Unternehmerbild verhindert, dass Frauen im gleichen Ausmaße wie Männer Unternehmen gründen, weiterführen und in wachsenden Unternehmen Arbeitgeber- und Führungsfunktionen übernehmen und damit Arbeitsplätze schaffen. Die Autorinnen stellen zur Überprüfung dieser Hypothese einige Auszüge aus den narrativen, problemzentrierten Interviews mit Unternehmerinnen und Unternehmern vor und erläutern ihre Typologie des Unternehmertums, welche die Typen 'Normalunternehmer', 'Step-by-Step', 'Crisis' und 'Bricoleur' umfasst. Angesichts der beobachteten Vielfalt des Unternehmertums plädieren sie für eine Verflüssigung des hegemonialen unternehmerischen Leitbildes und die Schaffung einer 'Entrepreneurial Diversity'
Die Erosion des Normalunternehmertums als Chance für eine notwendige Entrepreneurial Diversity
(2007)
Digitale Brücken nach Nepal
(2003)
Diversity Management
(2001)
This paper develops a framework for understanding the relationships between approaches to learning adopted by students in the context of higher education and the culture of the country they were brought up in. The paper, after examining the more widely used Kolb's learning styles, opts for another categorisation, namely the so called learning approaches developed by Entwistle and others (for example, Entwistle and Ramsden, 1983; Biggs, 1987; Entwistle, 1992; Tait, Entwistle and McCune, 1998; Biggs, Kember and Leung, 2001). Each of the main categories of learning approaches identified by his school, namely, deep, surface apathetic, and strategic are related to Hofstede's cultural dimensions, namely, power distance, individualism vs. collectivism, uncertainty avoidance, long vs. short time orientation and masculinity vs. femininity and a series of hypotheses developed that could be tested in cross cultural samples. This study would give practical hints on students moving out to study in different cultures (e.g. for higher education) and for teachers dealing with students from multiple cultures.
(PDF) Does culture influence learning styles in higher education?. Available from: https://www.researchgate.net/publication/254836756_Does_culture_influence_learning_styles_in_higher_education [accessed Jul 09 2018].
When an open quantum system is driven by an external time-dependent force, the coupling of the driving to the central system is usually included, whereas the impact of the driving field on the bath is neglected. We investigate the effect of a quantum bath of linearly driven harmonic oscillators on the relaxation dynamics of a quantum two-level system which is not directly driven. In particular, we calculate the frequency-dependent response of the system when the bath is subject to Dirac and Gaussian driving pulses. We show that a time-retarded effective force on the system is induced by the driven bath which depends on the full history of the perturbation and the spectral characteristics of the underlying bath. In particular, when a structured Ohmic bath with a pronounced Lorentzian peak is considered, the dynamical response of the system to a driven bath is qualitatively different than that of the undriven bath. Specifically, additional resonances appear which can be directly associated with a Jaynes-Cummings-like effective energy spectrum.
Efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes
(2015)
Environmental rocking ratchet: Environmental rectification by a harmonically driven avoided crossing
(2017)
We propose a rocking ratchet designed as a symmetric quantum two-state system driven by a single periodic harmonic force and influenced symmetrically by thermal fluctuations. We show that the necessary broken symmetry can dynamically be achieved by a thermal environment that couples to the energy difference between the two states and the tunnel coupling between them. The quantum two-state system is driven by the harmonic periodic drive through its avoided crossing. The correspondingly driven dissipative quantum dynamics results on average in a finite population difference between both states. This then causes directed particle transport.
We present a scheme for cooling a vibrational mode of a magnetic molecular nanojunction by a spin-polarized charge current upon exploiting the interaction between its magnetic moment and the vibration. The spin-polarized charge current polarizes the magnetic moment of the nanoisland, thereby lowering its energy. A small but finite coupling between the vibration and the magnetic moment permits a direct exchange of energy such that vibrational energy can be transferred into the magnetic state. For positive bias voltages, this generates an effective cooling of the molecular vibrational mode. We determine parameter regimes for the cooling of the vibration to be optimal. Although the flowing charge current inevitably heats up the vibrational mode via Ohmic energy losses, we show that due to the magnetomechanical coupling, the vibrational energy (i.e, the effective phonon temperature) can be lowered below 50% of its initial value, when the two leads are polarized anti-parallel. In contrast to the cooling effect for positive bias voltages, net heating of the vibrational mode occurs for negative bias voltages. The cooling effect is enhanced for a stronger anti-parallel magnetic polarization of the leads, while the heating is stronger for a larger parallel polarization. Yet, dynamical cooling is also possible with parallel lead alignments when the two tunneling barriers are asymmetric.