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1
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Oscillations in Magnetoresistance and Interlayer coupling in Magnetic Sandwich Structures

100%
Barnaś J., Bułka B.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
253-256
EN
Kubo formalism is used to calculate the magnetoresistance due to magnetization rotation in a structure consisting of two magnetic films separated by a nonmagnetic layer. In the approximation of a uniform relaxation time for each layer, the oscillatory term in magnetoresistance corresponds to the oscillation period which depends on the potential barriers at the interfaces. This period is longer than the oscillation period observed in the coupling parameter.
2
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Logic Operations of Charge Qubit in a Triple Quantum Dot

100%
Ptaszyński K., Bułka B.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-30-A-32
EN
Studies for a single charge qubit and two capacitively coupled qubits built on triple quantum dots are presented. We show feasibility of implementing two-qubit gate operations, e.g. the CPHASE gate can be implemented with the fidelity higher than 99% for strong couplings.
3
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Dark States and Transport through Quantum Dots

100%
Tooski S., Bułka B.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1231-1233
EN
We consider current through triple and quadruple quantum dot systems in an in-plane electric field and in the sequential tunneling regime. The electric field breaks symmetry of the system and can trap electron in a dark state in which current flow can completely be blocked. Consequently rotating the electric field, one can observe current oscillations and blockades due to dark state.
4
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Enhancement of Current Auto- and Cross-Correlations in Double Quantum Dots

100%
Michałek G., Bułka B.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
117-119
EN
Studies of an enhancement of current shot noises are presented for a device of two large quantum dots coupled capacitively. We analyze current-current correlation functions, and show that a dynamical Coulomb blockade is responsible for an enhancement of the Fano factors. This process can lead also to an electron bunching and positive current cross-correlations. Our theoretical results are discussed in light of recent shot noise experiments.
5
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Singlet-Triplet Switching Induced by Electric Field in Triple Quantum Dots

100%
Łuczak J., Bułka B.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1195-1197
EN
We analyze influence of an external electric field on magnetic properties of a triple quantum dot system in a triangular and linear geometry. The system contains four electrons and is described by an extended Hubbard model which includes electron correlations and exchange processes. The electric field leads to splitting of energy levels (the Stark effect) and to transition between the singlet and triplet states.
6
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Interference Effects in Three-Terminal Hybrid Systems with Quantum Dots

100%
Michałek G., Bułka B.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
981-983
EN
Conductance in a three-terminal hybrid system with two quantum dots is analyzed. Our attention is focused on an influence of decoherence on interference effects in the Andreev transport. In particular, we have found that a change of coupling to the third electrode can strongly modify a shape of the Fano-type resonances. This effect is due to activation of nonlocal Andreev reflection (CAR) processes.
7
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Dynamics of a Charge Qubit Encoded in a Double Quantum Dot

100%
Łuczak J., Bułka B.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
748-750
EN
We study the short time dynamics of a charge qubit encoded in two coherently coupled quantum dots connected to external electrodes. In the regime of sequential tunneling the waiting time distribution is used to investigate in details statistics of the tunneling events and their correlations. We show that the coherent rotation of the qubit state on the Bloch sphere can be seen in tunneling events when an electron is injected and leave the system. Decoherence, relaxation of the qubit state as well as leakage processes are studied by means of transient currents.
8
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Theoretical Studies of Quantum Interference in Electronic Transport through Carbon Nanotubes

100%
Babiaczyk W., Bułka B.
|
|
issue 4-5
597-602
EN
We performed studies of coherent electronic transport through a single walled carbon nanotube. In the calculations multiple scattering on the contacts and interference processes were taken into account. Conductance is a composition of contributions from different channels. We studied also spin-dependent transport in the system with ferromagnetic electrodes. The magnetoresistance is large and shows large oscillations, it can be even negative in some cases.
9
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Cross-Correlations and Charge Pumping in Shot Noise οf Coupled Quantum Dot System

100%
Michałek G., Bułka B.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
879-881
EN
We analyze current auto- and cross-correlations in the system of two capacitively coupled large quantum dots. Our attention is focused on the strong inter-dot coupling when an electron transfer through one of the quantum dots induces charge pumping through the second quantum dot. We show individual contributions to shot noise from various tunneling processes in the charge space.
10
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Quantum Transport in Thin-Film Structures

100%
Bułka B., Barnaś J.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
465-468
EN
General quantum-mechanical description of electronic transport in thin-film structures, which is based on the Kubo approach, is presented and applied to a single film with ideal surfaces. The cases of a constant chemical potential and a constant particle number are considered and analysed numerically.
11
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Current Shot Noise and Bunching of Electrons in Multilevel Quantum Dots

100%
Michałek G., Bułka B.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
27-30
EN
Currents and their fluctuations in multilevel quantum dots are studied theoretically in the limit of sequential tunneling. The spin degrees of freedom, many-body electronic states (singlet and triplet) as well as relaxation processes between the levels of the quantum dots are considered. In general, due to the rapid relaxation processes the shot noise is sub-Poissonian, however for a large polarization of the outgoing currents from the singlet and triplet states one gets the super-Poissonian type of the shot noise due to the bunching of tunneling events.
12
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Negative Differential Resistance and Super-Poissonian Shot Noise in a System of Single Electron Transistors

100%
Michałek G., Bułka B.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
431-436
EN
Currents and their fluctuations in two capacitively coupled single electron transistors were studied within the sequential tunneling approach. A special attention was focused on the effect of the negative differential resistance, which appears due to the Coulomb interactions of accumulated charges on both the single electron transistors. In this case large polarization fluctuations are activated, which results in a significant enhancement of the current shot noise.
13
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Current Fluctuations in Ferromagnetic Tunnel Junctions

81%
Bułka B., Martinek J., Michałek G., Barnaś J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
423-426
EN
Current shot noise in a double junction consisting of a small metallic grain connected to two ferromagnetic electrodes is analysed in the limit of sequential tunneling. We show that, apart from charge fluctuations, there are strong spin fluctuations. We also show that two distinct relaxation processes can be distinguished in the frequency dependent current noise: one in a low frequency range and corresponding to spin fluctuations and another one in a high frequency range corresponding to charge fluctuations.
14
Content available remote

Statistics of Tunneling Events in Three-Terminal Hybrid Devices with Quantum Dot

81%
Michałek G., Bułka B., Domański T., Wysokiński K.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
391-393
EN
We investigate statistics of the tunneling events in the short time limit in terms of the waiting time distribution (WTD), defined as the probability for a delay time between two subsequent transitions of particles, and consider it for a quantum dot (QD) strongly coupled to a superconducting and weakly coupled to two normal electrodes. Our study focuses on the WTD in the subgap transport, when coherent exchange of the Cooper pairs occurs between the QD and the superconductor. The dynamics can be described in terms of a Markovian generalized master equation for the reduced density matrix. We observe coherent oscillations between the Andreev bound states in the correlated jumps, both for the local and non-local WTDs. In addition the analysis of the transient currents give us some insight into dominant relaxation processes in short time scales.
15
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Interplay of Kondo and Fano Resonance in Electronic Transport in Nanostructures

81%
Bułka B., Stefański P., Tagliacozzo A.
Acta Physica Polonica A
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2005
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vol. 108
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issue 4
555-569
EN
Quantum interference and electronic correlations are processes relevant for electronic transport in nanostructures. We present theoretical studies of transport for various models, which take into account these processes and describe the Fano resonance as well as many-body effects like the Kondo resonance. The results are compared with transport measurements performed on a small quantum dot strongly coupled to electrodes, a large semi-open quantum dot, a side-attached quantum dot to a quantum wire systems and a quantum dot embedded in the metallic ring. We show how conductance characteristics of the Kondo and the Fano resonance are modified in different situations.
16
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Linear and Non-Linear Response in T-Shaped Electron Waveguides

81%
Bek M., Bułka B., Wróbel J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
829-831
EN
We present theoretical studies of three-terminal ballistic junction in linear and non-linear regime. Various conductance and voltage dips and peaks are observed and their origin is explained as influence of the bend resistance and the threshold effect.
17
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Andreev Spectroscopy in Three-Terminal Hybrid Nanostructure

71%
Michałek G., Bułka B., Urbaniak M., Domański T., Wysokiński K.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
293-295
EN
We consider a hybrid three-terminal structure consisting of a quantum dot coupled to three leads, two normal and one superconducting. The current flowing between one of the normal and the superconducting electrodes induces voltage in the other normal (floating) electrode. The value of the induced voltage depends on the position of the Andreev levels in the quantum dot and is a measure of the interplay between the electron transfer and the subgap anomalous reflection processes. When the crossed (i.e. non-local) Andreev reflections dominate the induced potential in the normal electrode becomes negative. This situation occurs for the relatively strong coupling to the superconducting electrode and only outside the Coulomb blockade region. Taking the superconducting electrode as the voltage probe one gets additional information on competition of injected carriers.
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