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Resonances, dissipation and decoherence in exotic and artificial atoms
Stockholm University, Faculty of Science, Department of Physics. (Atomfysik)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There are several reasons why exotic and artificial atoms attract the interest of different scientific communities.In exotic atoms, matter and antimatter can coexist for surprisingly long times. Thus, they present a unique natural laboratory for high precision antimatter studies. In artificial atoms, electrons can be confined in an externally controlled way. This aspect is crucial, as it opens new possibilities for high precision measurements and also makes artificial atoms promising potential candidates for qubits, i.e. the essential bricks for quantum computation.The first part of the thesis presents theoretical studies of resonant states in antiprotonic atoms and spherical two-electron quantum dots, where well established techniques, frequently used for conventional atomic systems, can be applied after moderate modifications. In the framework of Markovian master equations, it is then demonstrated that systems containing resonant states can be approached as open systems in which the resonance width determines the environmental coupling. The second part of the thesis focuses on possible quantum computational aspects of two kinds of artificial atoms, quantum dots and Penning traps. Environmentally induced decoherence, the main obstacle for a practical realization of a quantum computer based on these devices, is studied within a simple phenomenological model. As a result, the dependence of the decoherence timescales on the temperature of the heat bath and environmental scattering rates is obtained.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 86 p.
Keyword [en]
quantum dissipation, quantum decoherence, open quantum systems, resonances
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-38153ISBN: 978-91-7447-027-7 (print)OAI: oai:DiVA.org:su-38153DiVA: diva2:306852
Public defence
2010-05-26, sal FR4, AlbaNova universitetscentrum, Roslagstullbacken 21, Stockholm, 13:15 (English)
Opponent
Supervisors
Available from: 2010-05-04 Created: 2010-03-29 Last updated: 2010-04-08Bibliographically approved
List of papers
1. Possibility of resonant capture of antiprotons by highly charged hydrogenlike ions
Open this publication in new window or tab >>Possibility of resonant capture of antiprotons by highly charged hydrogenlike ions
2009 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 51, no 2, 205-212 p.Article in journal (Refereed) Published
Abstract [en]

Recently, an experimetal setup was proposed by Lapierre et al (in Physics with ultra slow antiproton beams, AIP Conference Proceedings, edited by Y. Yamazaki and M. Wada (2005), vol. 793, p. 361) which would allow antiprotons and highly charged ions to collide repeatedly in an electron beam ion trap (EBIT) due to a nested trap configuration. As mentioned by the authors, such a setup may open the possibility to study antiproton capture into well-defined states through a resonant process which involves simultaneous electron excitation. In the present work, we give some theoretical estimations of the feasibility of that process.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-18895 (URN)10.1140/epjd/e2008-00273-1 (DOI)000263417700005 ()
Available from: 2009-02-16 Created: 2009-02-16 Last updated: 2011-05-25Bibliographically approved
2. Effects of screened Coulomb impurities on autoionizing two-electron resonances in spherical quantum dots
Open this publication in new window or tab >>Effects of screened Coulomb impurities on autoionizing two-electron resonances in spherical quantum dots
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 12, 125315- p.Article in journal (Refereed) Published
Abstract [en]

In a recent paper [Phys. Rev. B 78, 075316 (2008)], Sajeev and Moiseyev demonstrated that the bound-to-resonant transitions and lifetimes of autoionizing states in spherical quantum dots can be controlled by varying the confinement strength. In the present paper, we report that such control can in some cases be compromised by the presence of Coulomb impurities. It is demonstrated that a screened Coulomb impurity placed in the vicinity of the dot center can lead to bound-to-resonant transitions and to avoided-crossinglike-behavior when the screening of the impurity charge is varied. It is argued that these properties also can have impact on electron transport through quantum dot arrays.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-38124 (URN)10.1103/PhysRevB.81.125315 (DOI)000276248900099 ()
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2011-12-05Bibliographically approved
3. Description of resonance decay by Lindblad operators
Open this publication in new window or tab >>Description of resonance decay by Lindblad operators
2008 (English)In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 41, no 42, 425303- p.Article in journal (Refereed) Published
Abstract [en]

Using an analytical model potential which contains resonant and bound states, we show that the decay of the resonances can be simulated by Lindblad operators. For that purpose, the unitary time evolution of an initial Gaussian wave packet in the model potential is compared with the non-unitary time evolution, obtained by solving the Lindblad equation, of the same wave packet in a potential which coincides with the model potential in the region of interest but does not contain resonances. In the latter case, dissipative effects are accounted for by Lindblad operators which lead to phenomenological friction and diffusion constants in the equations of motion. We suggest how those constants can be determined in a non-heuristic way, being directly connected to the width of the resonance in the model potential which we calculate using the complex rotation method.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-15053 (URN)10.1088/1751-8113/41/42/425303 (DOI)000259699400016 ()
Available from: 2009-02-16 Created: 2009-02-16 Last updated: 2011-05-25Bibliographically approved
4. Environmentally induced shift of the quantum arrival time
Open this publication in new window or tab >>Environmentally induced shift of the quantum arrival time
2009 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. A80, 052112- p.Article in journal (Refereed) Published
Abstract [en]

Usinga simple model potential, we study the effects of weakMarkovian dissipation on the quantum arrival time. The interaction withthe environment is incorporated into the dynamics through a Markovianmaster equation of Lindblad type, which allows us to comparetime-of-arrival distributions and approximate crossing probabilities for different dissipation strengthsand temperatures. We also establish a connection to an earlierstudy where quantum tunneling with dissipation was investigated, which leadsus to some conclusions concerning the formulation of the continuityequation in the Lindblad theory.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-32116 (URN)10.1103/PhysRevA.80.052112 (DOI)000272310000031 ()
Available from: 2009-12-03 Created: 2009-12-03 Last updated: 2011-05-25Bibliographically approved
5. Estimation of the spatial decoherence time in circular quantum dots
Open this publication in new window or tab >>Estimation of the spatial decoherence time in circular quantum dots
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. B79, no 24, 245310- p.Article in journal (Refereed) Published
Abstract [en]

We propose a simple phenomenological model to estimate the spatial decoherence time in quantum dots. The dissipative phase space dynamicsis described in terms of the density matrix and the corresponding Wigner function, which are derived from a master equation with Lindblad operatorslinear in the canonical variables. The formalism was initially developed to describe diffusion and dissipation in deep inelastic heavy ioncollisions, but also an application to quantum dots is possible.It allows us to study the dependence of the decoherence rate on the dissipation strength, the temperature and an external magnetic field, which isdemonstrated in illustrative calculations on a circular GaAs one-electron quantum dot.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-29769 (URN)10.1103/PhysRevB.79.245310 (DOI)000267699700086 ()
Available from: 2009-09-14 Created: 2009-09-14 Last updated: 2011-05-25Bibliographically approved
6. On the Penning trap coherent states
Open this publication in new window or tab >>On the Penning trap coherent states
2009 (English)In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 42, no 27, 275305- p.Article in journal (Refereed) Published
Abstract [en]

Recently, a class of coherent states of a particle in a Penning trap was derived byFernandez and Velazquez (J. Phys. A: Math. Theor. 42 (2009) 085304).By means of the Wigner function and density matrix associated with these states,we show that they are fully consistent with Morikawa's definition of the decoherence degree and hence they provide apossibility to directly access the decoherence process in a Penning trap.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-29770 (URN)10.1088/1751-8113/42/27/275305 (DOI)000267137300018 ()
Available from: 2009-09-14 Created: 2009-09-14 Last updated: 2011-05-25Bibliographically approved
7. Environmental effects on the phase space dynamics and decoherence time scale of a charged particle in a Penning trap
Open this publication in new window or tab >>Environmental effects on the phase space dynamics and decoherence time scale of a charged particle in a Penning trap
2009 (English)In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 42, no 38, 385302- p.Article in journal (Refereed) Published
Abstract [en]

We study the time evolution of a charged particle in a Penning trap in the framework of open quantum systems. The interaction with the environment istaken into account by imposing Lindblad operators which are linear in the canonical variables. For the special case of a proton in an asymmetricPenning trap we compare the dynamics with earlier results obtained from the unitary time-dependent Schrödinger equation. A possibility to estimatethe spatial decoherence time of the system is discussed, and approximate decoherence time scales are given for different ions.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-29772 (URN)10.1088/1751-8113/42/38/385302 (DOI)000269579000018 ()
Available from: 2009-09-14 Created: 2009-09-14 Last updated: 2011-05-25Bibliographically approved

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