Dephasing of a quantum dot due to the Coulomb interaction with a gate electrode

Woodford, S. R.; Bringer, A.; Indlekofer, K. M.

doi:10.1103/physrevb.76.064306

Cited by 10 publications

(11 citation statements)

References 27 publications

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“…Without Born-Markov approximation, Wu et al had devised an analytical expression for the dynamical tunneling current using a perturbation treatment based on a unitary transformation [18,19]. Effects from Coulomb interaction between the dots and the gate electrodes with the formulation of kinetic equations have been presented by Woodford et al [20]. The diversity in the methodologies and issues concerned in the literature show the physical richness of this novel system.…”

Section: Introductionmentioning

confidence: 99%

Non-Markovian decoherence theory for a double-dot charge qubit

2008

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In this paper, we develop a non-perturbation theory for describing decoherence dynamics of electron charges in a double quantum dot gated by electrodes. We extend the Feynman-Vernon influence functional theory to fermionic environments and derive an exact master equation for the reduced density matrix of electrons in the double dot for a general spectral density at arbitrary temperature and bias. We then investigate the decoherence dynamics of the double dot charge qubit with back-action of the reservoirs being fully taken into account. Time-dependent fluctuations and leakage effects induced from the dot-reservoir coupling are explicitly explored. The charge qubit dynamics from the Markovian to non-Markovian regime is systematically studied under various manipulating conditions. The decay behavior of charge qubit coherence and the corresponding relaxation time T1 and dephasing time T2 are analyzed in details.

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Section: Introductionmentioning

confidence: 99%

Non-Markovian decoherence theory for a double-dot charge qubit

2008

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“…the experiments described in Ref. [44]) -the dynamical properties of such a configuration will not be notably different from the single-electrode model [204].…”

Section: Coulomb Interaction With the Gatementioning

confidence: 99%

“…From the point of view of the quantum dot, each electrode has two separate effects: the potential of each electrode statically defines the two quantum dots and each electrode exhibits a dynamical response to the motion of the electron. Since the potential of an electrode has a negligible effect on its Fermi level, plasma frequency and electron mean free path, each electrode will have a similar dynamical response [204]. Indeed, from the dynamical point of view, there is little difference between a system with several separate electrodes and a system with a single, large electrode; the primary differences are the increase of interaction area and the neglect of eddy currents, both of which are small effects in this system.…”

Section: Dephasing Of Charge Qubits 731 Difference Between Charge Amentioning

confidence: 99%

“…For charge qubits, I present only the important differences from the spin qubit investigation and the results; a more detailed account is available in Ref. [204] 1 . Hartree atomic units are used, except where otherwise stated.…”

Section: Overviewmentioning

confidence: 99%

“…Further details can be found in Ref. [204] Charge qubits have already been described in chapter 1. They consist of a pair of quantum dots separated by a tunnel barrier.…”

Section: Dephasing Of Charge Qubits 731 Difference Between Charge Amentioning

confidence: 99%

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Ultrafast Magnetization Dynamics

Woodford¹,

Blügel²

Magnetism

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This thesis addresses ultrafast magnetization dynamics from a theoretical perspective. The manipulation of magnetization using the inverse Faraday effect has been studied, as well as magnetic relaxation processes in quantum dots.The inverse Faraday effect -the generation of a magnetic field by nonresonant, circularly polarized light -offers the possibility to control and reverse magnetization on a timescale of a few hundred femtoseconds. This is important both for the technological advantages and for the deeper fundamental understanding of magnetization dynamics that can be gained. However, several aspects of the inverse Faraday effect have remained poorly understood. The question of whether light can manipulate magnetization alone or whether an additional angular momentum reservoir is needed, in particular, remains unanswered.This question is answered here: the light beam that causes the inverse Faraday effect provides the angular momentum required for the magnetization to precess. No other reservoir is needed. This implies that manipulation of the magnetization occurs on the timescale of a laser pulse, which can be made extremely short. Even magnetization reversal on this timescale could be possible, provided a material with a sufficiently strong magnetooptical response can be found. This is a technical challenge, not a fundamental obstacle.The Faraday effect in the presence of optical birefringence has also been analyzed. This effect has been used for imaging magnetization dynamics in transparent media on an ultrafast timescale, but transparent magnetic materials usually have a complex crystal structure and complicated optical properties, which render the relationship between Faraday rotation and magnetization unclear. We have shown that the Faraday effect can be used to measure the instantaneous magnetization, even in the presence of birefringence, provided certain experimental conditions are met. Suggestions concerning these experimental conditions are made.The relaxation of magnetization, particularly the relaxation of a spin in a quantum dot, has been studied. This problem is relevant to the fields of quantum computing and highly-multiplexed optical memory, both of which are of great current interest. We have investigated the interaction of the spin with a metallic electrode and calculated the dephasing and dissipation rates. We found that under current experimental conditions, this relaxation pathway is negligible compared to spin-phonon scattering, but as systems are miniaturized, interactions with electrodes become more important.The methods developed to study the relaxation of a spin were also applied to the relaxation of a charge in a double quantum dot, another important problem in quantum computing. Again, we found that the interaction with a gate electrode is generally much weaker than the interaction with phonons but may be important for smaller systems. Kurzfassung

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The Triangular and Coulomb Bound Potential Quantum Dot Qubit

Yin

Xiao

2013

J Low Temp Phys

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Dephasing of a quantum dot due to the Coulomb interaction with a gate electrode

Cited by 10 publications

References 27 publications

Non-Markovian decoherence theory for a double-dot charge qubit

Non-Markovian decoherence theory for a double-dot charge qubit

Ultrafast Magnetization Dynamics

The Triangular and Coulomb Bound Potential Quantum Dot Qubit

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