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1
Content available remote

Two-Photon Coherent Polarization Flipping of Confined Excitons

100%
Machnikowski P.
Acta Physica Polonica A
|
2007
|
vol. 112
|
issue 2
289-293
EN
A two-photon process leading to coherent transitions between the two circularly polarized exciton states in a quantum dot is studied. It is shown that optical flipping of the exciton polarization is possible with picosecond laser pulses. The process is closely related to two-photon Rabi oscillations of a biexciton but it is much more stable against shifts of the laser frequency.
2
Content available remote

Intermediate Band Formation and Intraband Absorption for Electrons in an Inhomogeneous Chain of Quantum Dots

64%
Bragar I., Machnikowski P.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 5
862-864
EN
We study the electron states of a chain of non-identical, vertically stacked quantum dots. We discuss how the pseudo-band formed of the ground states confined in the quantum dots disintegrates upon increasing the inhomogeneity of the electron energies and analyze the impact of localization on the intraband absorption from the pseudo-band to extended (bulk) states. We describe also the dependence of the intraband absorption spectrum on the quantum dot size.
3
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Collective Spontaneous Emission from Pairs of Quantum Dots: Long-Range vs. Short-Range Couplings

64%
Abdussalam W., Machnikowski P.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 5
865-867
EN
We study the spontaneous emission from a coherently delocalized exciton state in a double quantum dot as a function of the distance between the dots, focusing on the similarities and differences between the cases of radiative (long-range, dipole) and tunnel coupling between the excitons in the dots. We show that there may be no qualitative difference between the collective emission induced by these two coupling types in spite of their essentially different physical properties.
4
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Tunneling Transfer Protocol in a Quantum Dot Chain Immune to Inhomogeneity

64%
Korzekwa K., Machnikowski P.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 5
859-861
EN
We propose a quantum dot implementation of a quantum state transfer channel. The proposed channel consists of N vertically stacked quantum dots with the nearest neighbor tunnel coupling, placed in an axial electric field. We show that the system supports high-fidelity transfer of the state of a terminal dot both by free evolution and by adiabatic transfer. The protocol is to a large extent insensitive to inhomogeneity of the energy parameters of the dots and requires only a global electric field.
5
Publication available in full text mode
Content available

Collective Encoding of Quantum Information in a Quantum Dot Register

64%
Grodecka A., Machnikowski P.
Acta Physica Polonica A
|
2006
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vol. 110
|
issue 2
195-200
EN
We define the collective logical quantum bit as a state on an array of 2, 4, and 8 quantum dots. We show that such an array can be controlled with less phonon-induced pure dephasing than a single dot. We calculate the dephasing accompanying a single-qubit operation on the collective logical qubit by means of perturbative method describing the open system evolution under arbitrary driving.
6
Publication available in full text mode
Content available

Phonon-Induced Dephasing of Optically Driven Exciton States in Quantum Dots: Spectral Interpretation

64%
Machnikowski P., Jacak L.
Acta Physica Polonica A
|
2005
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vol. 108
|
issue 5
761-767
EN
We discuss phonon-induced perturbation of optically driven coherent dynamics of a confined exciton in a quantum dot in terms of nonlinear spectra of the driving pulse. Damping of pulse-area-dependent Rabi oscillations and phonon-assisted pumping of optically inactive states are analyzed.
7
Content available remote

Collective Spontaneous Emission from a System of Quantum Dots

64%
Abdussalam W., Machnikowski P.
Acta Physica Polonica A
|
2012
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vol. 122
|
issue 6
994-996
EN
We study the spontaneous emission from a regular lateral array or a randomly distributed ensemble of quantum dots under strong excitation (full inversion) conditions. We focus on the similarities and differences between the cases of random and regular arrangement of the dots and show that there is very little difference between the evolution of luminescence in these two cases, both for identical dots and for a realistically inhomogeneously broadened ensemble. This means that the enhanced emission or superradiance effect is not due to accidental clustering of pairs of dots. Moreover, we point out that observation of an enhanced emission under weak excitation does not prove that true superradiance will develop in a fully inverted system.
8
Content available remote

Electron States, Phonon-Assisted Relaxation and Tunneling in Self-Assembled Quantum Dot Molecules in an Electric Field

64%
Gawarecki K., Machnikowski P.
Acta Physica Polonica A
|
2011
|
vol. 119
|
issue 5
637-639
EN
We present a theoretical analysis of the phonon-assisted relaxation in a system composed of two self-assembled vertically stacked quantum dots. We construct realistic model, which takes into account the geometry and strain distribution in the system. We calculate phonon-assisted relaxation rates between the two lowest states (in one- and two-electron cases). The relaxation rates and energy levels are studied as a function of external (axial) electric field and geometry of the structure (dot sizes). We show that the relaxation times can be as low as 1 ps but efficient relaxation occurs only for very finely tuned dots.
9
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Phonon-Assisted Excitation Transfer in Quantum Dot Molecules

64%
Rozbicki E., Machnikowski P.
Acta Physica Polonica A
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2007
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vol. 112
|
issue 2
197-202
EN
We derive a quantum-kinetic description of phonon-assisted Förster transfer between two coupled quantum dots (a quantum dot molecule). We show that the exciton state decays to the ground state of the quantum dot molecule via a combination of the Rabi rotation and exponential decay. For moderately spaced dots this process takes place on a picosecond timescale.
10
Content available remote

Four-Wave Mixing Spectroscopy of Quantum Dot Molecules

64%
Sitek A., Machnikowski P.
Acta Physica Polonica A
|
2007
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vol. 112
|
issue 2
167-172
EN
We study theoretically the nonlinear four-wave mixing response of an ensemble of coupled pairs of quantum dots (quantum dot molecules). We discuss the shape of the echo signal depending on the parameters of the ensemble: the statistics of transition energies and the degree of size correlations between the dots forming the molecules.
11
Content available remote

Phonon-Induced Pure Dephasing of Two-Electron Spin States in Vertical Quantum Dot Molecules

64%
Roszak K., Machnikowski P.
Acta Physica Polonica A
|
2009
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vol. 116
|
issue 5
877-878
EN
Phonon-induced dephasing of two-electron spin states in two vertically stacked self-assembled GaAs/InGaAs quantum dots is studied. A pure dephasing process due to elastic phonon scattering is found to dominate at low temperatures. This process is independent of the spin-orbit coupling and does not require the presence of a magnetic field. It relies on interdot tunneling and the Pauli principle, which make the double quantum dot gate for spin based quantum computing possible, and therefore cannot be avoided.
12
Content available remote

Phonon-Assisted Tunneling of an Electron in a Strained Self-Assembled Quantum Dot Molecule

64%
Pochwała M., Machnikowski P.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 5
1285-1291
EN
We calculate phonon-assisted relaxation rates in a self-assembled quantum dot molecule. The calculation is based on wave functions obtained within an envelope function approach, including strain effects. The single-phonon relaxation is shown to be efficient for separations between the dots around 10 nm when, in addition, the dots are brought close to resonance.
13
Content available remote

Superradiance Effects in the Linear and Nonlinear Optical Response of Quantum Dot Molecules

64%
Sitek A., Machnikowski P.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1355-1360
EN
We calculate the linear optical response from a single quantum dot molecule and the nonlinear, four-wave-mixing response from an inhomogeneously broadened ensemble of such molecules. We show that both optical signals are affected by the coupling-dependent superradiance effect and by optical interference between the two polarizations. As a result, the linear and nonlinear responses are not identical.
14
Content available remote

Second-Order Resonant Polaron in a Self-Assembled Quantum Dot

64%
Kaczmarkiewicz P., Machnikowski P.
Acta Physica Polonica A
|
2008
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vol. 114
|
issue 5
1139-1144
EN
We calculate numerically the spectrum of a polaron in a quantum dot in the region of resonance with two-phonon states. We show that the experimental data can be reproduced by a model that does not depend on any adjustable parameters.
15
Content available remote

Multiple Exciton Generation in InAs Nanocrystals

64%
Kowalski P., Machnikowski P.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1187-1192
EN
We study a simple theoretical model of multiple exciton generation by a single high-energy photon absorbed in an InAs nanocrystal. We calculate the Coulomb matrix element for the electron-trion coupling in an InAs nanocrystal and show that due to the resulting coupling between single-pair and two-pair states the latter becomes weakly optically active.
16
Content available remote

Accuracy of Effective Mass Equation for a Single and Double Cylindrical Quantum Dot

52%
Mielnik-Pyszczorski A., Gawarecki K., Machnikowski P.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 2
376-379
EN
In this contribution we study the accuracy of various forms of electron effective mass equation in reproducing spectral and spin-related features of quantum dot systems. We compare the results of the standard 8 band k·p model to those obtained from effective mass equations obtained by perturbative elimination procedures in various approximtions for a cylindrical quantum dot or a system of two such dots. We calculate the splitting of electronic shells, the electron g-factor and spin-orbit induced spin mixing and show that for a cylindrical dot the g-factor is reproduced very exactly, while for the two other quantities the effective mass equation is much less accurate.
17
Publication available in full text mode
Content available

Complete and Partial Loss of Entanglement Due to a Phonon-Assisted Dephasing Process

52%
Roszak K., Machnikowski P., Jacak L.
Acta Physica Polonica A
|
2006
|
vol. 110
|
issue 3
331-336
EN
We study the evolution of entanglement between two excitons in a double quantum dot system coupled to a super-Ohmic reservoir. As expected entanglement is more fragile than local coherence, but, surprisingly, for a set of pure states disentanglement can be complete in a finite time under conditions that lead to the usual partial pure-dephasing.
18
Publication available in full text mode
Content available

Phonon-Induced Dephasing in Quantum Dots - Interpretation in Terms of Information Leakage

52%
Roszak K., Machnikowski P., Jacak L.
Acta Physica Polonica A
|
2006
|
vol. 110
|
issue 3
325-330
EN
We show that the phonon-induced pure dephasing of excitons in quantum dots can be interpreted in terms of information leakage from the carrier subsystem to the lattice environment. We derive a quantitative relation between the coherence of the system, as manifested by the amplitude of the coherent optical polarization, and the amount of available which path information on the system state, quantified by the distinguishability of states.
19
Content available remote

Nonlinear Oscillations in New Anharmonic Potential

52%
Konwent H., Machnikowski P., Radosz A.
Acta Physica Polonica A
|
1996
|
vol. 89
|
issue 4
481-493
EN
The classical equation of motion for a particle moving in the new double-well potential V(x) = ½ V_{0}(A cosh ax - 1)^{2} is solved exactly for different values of the parameter A and the energy constant E. The solutions in various special cases are discussed.
20
Content available remote

Carrier Trapping in a Quantum Dash: Optical Signatures

52%
Kaczmarkiewicz P., Machnikowski P., Kuhn T.
Acta Physica Polonica A
|
2012
|
vol. 122
|
issue 6
997-1000
EN
We theoretically study the optical properties and the electronic structure of highly elongated quantum dots (quantum dashes) and show how geometrical fluctuations affect the excitonic spectrum of the system. The dependence of the absorption intensities on the geometrical properties (depth and length) of the trapping center in a quantum dash is analyzed and the dependence of the degree of the linear polarization on these geometrical parameters is studied.
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