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1
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Decoherence and Noise in Loschmidt Echo Experiments

100%
Alicki R., Miklaszewski W., Pogorzelska M.
Acta Physica Polonica A
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2006
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vol. 109
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issue 1
121-129
EN
We discuss some recent results concerning the decoherence in controlled quantum open systems within the mathematical setting corresponding to motion reversal experiments (the Loschmidt echo). We compare the case of randomly chosen sequence of unitary dynamical maps with the case of a constant dynamics corresponding to a classically chaotic evolution. The interplay between chaos and decoherence is illustrated by the new numerical results on the quantum Arnold cat map perturbed by a measurement process. Open problems related to the simple operational characterization of the decoherence strength are discussed.
2
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Carrier Spin Dephasing during Spin-Preserving Tunneling in Coupled Quantum Dots

63%
Krzykowski M., Gawełczyk M., Machnikowski P.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1165-1168
EN
In this contribution we study carrier tunneling in a system consisting of a pair of coupled quantum dots. We predict the presence of a spin dephasing channel in such a system, which is associated with a "welcher-weg" type of decoherence process occurring during carrier tunneling. In our model such a process is caused by a mismatch of g-factor values in two quantum dots in the presence of external magnetic field. This leads to a mismatch in spin Zeeman splitting between the dots and, in consequence, to the distinguishability of phonons emitted during the tunneling of carriers with opposite spins. Thus we demonstrate a process of spin dephasing without any direct spin-environment coupling present in the model.
3
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Accuracy of Effective Mass Equation for a Single and Double Cylindrical Quantum Dot

63%
Mielnik-Pyszczorski A., Gawarecki K., Machnikowski P.
Acta Physica Polonica A
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2017
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vol. 132
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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.
4
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Phonon-Induced Pure Dephasing of Two-Electron Spin States in Vertical Quantum Dot Molecules

51%
Roszak K., Machnikowski P.
Acta Physica Polonica A
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2009
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vol. 116
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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.
5
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Singlet-Triplet Dephasing in Asymmetric Quantum Dot Molecules

51%
Marcinowski Ł., Roszak K., Machnikowski P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
874-876
EN
We discuss pure dephasing of singlet-triplet superpositions in two-electron double quantum dots due to elastic phonon scattering. We generalize our previous results to a system built of two non-identical dots. We show that the asymmetry must be very strong in order to considerably affect the dephasing rate.
6
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Investigation of a Two-Qubit Decoherence by Using Bloch Vectors

51%
Ahmadi F., Jami S.
Acta Physica Polonica A
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2014
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vol. 125
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issue 5
1088-1093
EN
The loss of the coherence happens due to the interaction between the desired system and its surroundings. Addressing decoherence is one of the main concepts in the study of quantum channels to access their potential for various scale. In this process the information of the system is penetrated into the environment. Therefore, the measurement of the environment could be used as the error correction method. Phase damping channels principally belong to random unitary channels and can be corrected by classical information. This paper presents a method to generate non-random unitary phase damping channels based on the Bloch vectors in two qubits systems. A phase damping channel which consisted of a two qubits system and a single qubit environment was investigated. The results demonstrated that the phase damping channels belong to random unitary dynamics if the three-dimensional tetrahedron volume spanned by the Bloch vectors in ℝ^3 is not zero, or, the same hyperplane in ℝ^3 was not pointed by the Bloch vectors. It is found that the Bell state belongs to random unitary class and can be corrected based on classical information obtained from environmental measurements.
7
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Non-Markovian Dynamic of Gaussian Quantum Discord in Continuous-Variable Systems

51%
Liu X., Wu W.
Acta Physica Polonica A
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2014
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vol. 126
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issue 3
652-656
EN
We show the special dynamic characteristic of Gaussian quantum discord, exhibited by two-mode Gaussian symmetric squeezed thermal states (STS) in continuous-variable (CV) systems with a common non-Markovian environment, is definitely different from Markov processes. We demonstrate that Gaussian quantum discord can be created whenever the information flow from environment back to the system. We also show that the rate of decrease for Gaussian quantum discord is related to the coupling constant. We discover that the initial value of Gaussian quantum discord is determined by the average number of thermal photons of the system.
8
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Quantum Fisher Information of Bipartitions of W States

51%
Ozaydin F., Altintas A., Yesilyurt C., Bugu S., Erol V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 4
1233-1235
EN
We study the quantum Fisher information (QFI) of W states and W-like states under decoherence. In particular, we find that on the contrary to amplitude damping and depolarizing decoherence, a W-like state of 3 qubits obtained by discarding 1 qubit of a genuine W state of 4 qubits is more robust than a genuine W state of 3 qubits under amplitude amplifying and phase damping decoherence.
9
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Nonexistence of the Classical Trajectories in the Stern-Gerlach Experiment

51%
Arsenijević M., Dugić M.
Acta Physica Polonica A
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2010
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vol. 117
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issue 5
760-763
EN
The Stern-Gerlach experiment is a paradigm of the quantum measurement of spin. Its physical interpretation is in intimate relation with the physical basis of the current research in the atomic (molecular) nanofabrication procedures. Nevertheless, interpretation of the experiment is an open issue yet. Here, we give the arguments for the physical nonexistence of the so-called classical trajectories of the atoms (molecules) in front of the screen. Some nanotech-related consequences are distinguished.
10
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An Optical Setup for Deterministic Creation of Four Partite W state

51%
Yesilyurt C., Bugu S., Diker F., Altintas A., Ozaydin F.
Acta Physica Polonica A
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2015
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vol. 127
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issue 4
1230-1232
EN
In order to create polarization based entanglement networks of W₄ state, we propose an optical setup, which uses only four horizontally polarized photons as resource which implies no entanglement requirement as a resource. This setup can generate target state deterministically, by operating several quantum optical gates, which can be realized with current photonics technology. The setup we propose is composed of one Not, two Hadamard, five Controlled Not (CNot) and one Toffoli gate.
11
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The Control of Entanglement in a Damped Jaynes-Cummings Model by Transient Effects

51%
Kayhan H.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
256-258
EN
In this work, we study the entanglement dynamics of the damped Jaynes-Cummings model with the transient effects modeled as the linear sweep of the coupling coefficient between the atom and the field. We show that the decoherence of the entanglement can be controlled by the transient effects under the influence of damping. These effects can accelerate and can decelerate the decoherence of the entanglement during the time-evolution of the system, by adjusting the frequency of the Rabi oscillations.
12
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Entanglement in Open Quantum Systems

51%
Buchleitner A., Carvalho A., Mintert F.
Acta Physica Polonica A
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2007
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vol. 112
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issue 4
575-588
EN
We give a compact review of some of our recent results on the quantification, the measurement, and the time evolution of entanglement in open quantum systems of variable structure and dimension. Also a first experimental implementation is briefly discussed.
13
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Collective Spontaneous Emission from Pairs of Quantum Dots: Long-Range vs. Short-Range Couplings

51%
Abdussalam W., Machnikowski P.
Acta Physica Polonica A
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2011
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vol. 120
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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.
14
Publication available in full text mode
Content available

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

51%
Machnikowski P., Jacak L.
Acta Physica Polonica A
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2005
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vol. 108
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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.
15
Content available remote

Disorder-Assisted Exciton Transport

51%
Scholak T., Zech T., Wellens T., Buchleitner A.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-89-A-94
EN
We discuss the possibly constructive role of disorder for the optimization of exciton transport in the FMO (Fenna-Matthews-Olson) light harvesting complex. Our analysis, which models the FMO as a 3D random graph, demonstrates the existence of a small fraction of optimal, though highly asymmetric, non-periodic conformations, which yield near-to-optimal coherent excitation transport. We argue that, on transient time scales, such quantum interference enhanced transport does always better than stochastic activation.
16
Publication available in full text mode
Content available

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

51%
Roszak K., Machnikowski P., Jacak L.
Acta Physica Polonica A
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2006
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vol. 110
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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.
17
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Fidelity Decay in Chaotical and Random Systems

51%
Kohler H.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-119-A-126
EN
Fidelity is the overlap of wave functions with the same initial state propagated in time by slightly different Hamiltonians. Its behavior depends crucially on the choice of the initial wave function state. We review two cases: first, the initial state is random. In this case a simple analytic relation with parametric spectral correlations can be established. The latter quantity is completely determined by the spectral data and can therefore be measured, without knowledge about the wave function. Second, the initial state is an eigenstate of the unperturbed system. In this case fidelity is identical to the survival probability. We find unexpected features like revival and non-ergodicity. In this case fluctuations around the mean are large and the full fidelity distribution becomes a non-trivial function. The full fidelity distribution can be calculated in the long time limit and for small perturbations.
18
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Fidelity in Quasi-1D Systems as a Probe for Anderson Localization

51%
Bodyfelt J., Zheng M., Kottos T., Kuhl U., Stöckmann H.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
756-764
EN
We analyze the echo dynamics in quasi-one-dimensional random media to investigate how the transition from localization to delocalization is encoded in its temporal decay properties. Our analysis extends from the standard perturbative regime corresponding to small perturbations (with respect to the mean level spacing) in the echo dynamics, out to the Wigner decay regime. On the theoretical side, our results rely on a banded random matrix modeling, and show in the localized regime under small perturbations a novel decay of the fidelity (Loschmidt echo), differing from the typical Gaussian decay seen within both diffusive and chaotic systems. For larger perturbation strengths, typical Wigner exponential decays are observed. Scattering echo measurements are performed experimentally within a quasi-1D microwave cavity randomly populated with point-like scatterers. Agreements are observed between experiments, numerics, and theoretical predictions.
19
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Collective Spontaneous Emission from a System of Quantum Dots

51%
Abdussalam W., Machnikowski P.
Acta Physica Polonica A
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2012
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vol. 122
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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.
20
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Entanglement and Statistical Properties of a System Consisting of Three-Level Atom Interacting with a Nonlinear Kerr Medium Field

51%
Abdel-Khalek S., Al-Rajhi M., Berrada K.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1083-1088
EN
In this paper, we present a proper quantum system to perform different tasks of quantum information processing with optimal conditions. We study the populations, entanglement, and nonclassical properties of a system consisting of three level atom interacting with a nonlinear Kerr medium field constructed in the framework of generalized Heisenberg algebra. We quantify these quantities in terms of different parameters involved in the whole system considering the case of moving and stationary atom in the real experimental meaning of the coupling constant. The nonlinearity introduced by these kinds of fields play a useful role to create high amount of entanglement during the time evolution. Interestingly, the relationship between the degree of nonlinearity and robust of entanglement is explored in this present model.
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