Wissenschaftliche Publikationen
Nikolai Bolik studiert in den Jahren 2018 – 2024 theoretische Physik an der Universität Heidelberg, mit einem Fokus auf statistische Physik und Quantenmechanik. Im Rahmen seiner Forschung beschäftigt er sich intensiv mit der Physik ultrakalter Quantengase. Dabei kombiniert er theoretische Konzepte numerischen Methoden. Ab 2025 promoviert er am Institut für Computerwissenschaften an der Universität Heidelbserg in der Arbeitsgruppe Artificial Intelligence for Programming, wo er moderne KI-Systeme beforscht.
Spontaneous-emission-induced ratchet in atom-optics kicked-rotor quantum walks (PRA 2024)
Nikolai Bolik und Sandro Wimberger
Abstract
Quantum walks have gained significant attention over the past decades, mainly because of their variety of implementations and applications. Atomic quantum walks are typically subject to spontaneous emissions arising from the control fields. We investigate spontaneous emission in an atom-optics kicked-rotor quantum walk. Here, spontaneous emission occurs naturally due to the driving by the kicks, and it is generally viewed as a nuisance in the experiment. We find, however, that spontaneous emission may induce asymmetries in an otherwise symmetric quantum walk. Our results underscore the utility of spontaneous emission and the application of the asymmetric evolution in the walker’s space, i.e., for the construction of a quantum walk ratchet or for Parrondo-like quantum games. This highlights the potential for reinterpreting seemingly adverse effects as beneficial under certain conditions, thus broadening the scope of quantum walks and their applications.
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Detecting topological phase transitions in a double kicked quantum rotor (PRA 2022)
Nikolai Bolik, Caspar Groiseau, Jerry H. Clark, Gil S. Summy, Yingmei Liu, and Sandro Wimberger
Abstract
We present a concrete theoretical proposal for detecting topological phase transitions in double kicked atom-optics kicked rotors with internal spin-1/2 degree of freedom. The implementation utilizes a kicked Bose-Einstein condensate evolving in one-dimensional momentum space. To reduce the influence of atom loss and phase decoherence, we aim to keep experimental durations short while maintaining a resonant experimental protocol. Experimental limitations induced by phase noise, quasimomentum distributions, symmetries, and the ac-Stark shift are considered. Our results thus suggest a feasible and optimized procedure for observing topological phase transitions in quantum kicked rotors.
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Light-shift-induced behaviors observed in momentum-space quantum walks (PRA 2022)
Nikolai Bolik, Caspar Groiseau, Jerry H. Clark, Alexander Gresch, Siamak Dadras, Gil S. Summy, Yingmei Liu, and Sandro Wimberger
Abstract
Over the last decade there have been many advances in studies of quantum walks (QWs) including a momentum-space QW recently realized in our spinor Bose-Einstein condensate system. This QW possessed behaviors that generally agreed with theoretical predictions; however, it also showed momentum distributions that were not adequately explained by the theory. We present a theoretical model which proves that the coherent dynamics of the spinor condensate is sufficient to explain the experimental data without invoking the presence of a thermal cloud of atoms as in the original theory. Our numerical findings are supported by an analytical prediction for the momentum distributions in the limit of zero-temperature condensates. This current model provides more complete explanations to the momentum-space QWs that can be applied to study quantum search algorithms and topological phases in Floquet-driven systems..
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Supplementary Material
The supplementary material includes full derivations and additional numerical testings which are referenced but not explicitly presented in the main article. We present these additional informations for transparancy in our reasoning.
Thesis
Decoherence and Dissipation in Open Quantum Systems (Master Thesis)
Abstract
The study of open quantum systems is crucial for understanding physics under realistic conditions given by the interaction of quantum mechanical systems with their environment. This thesis investigates the Dynamics of two distinct open Quantum systems, consisting of ultracold atoms in optical lattices. First, we explore symmetry properties in atom optics kicked rotor quantum walks influenced by spontaneous emissions (SE). We demonstrate that SE induces asymmetries in otherwise symmetric quantum walks. This finding is particularly interesting as it changes the typical perspective on SE, which is generally considered a nuisance. In our study, SE enables the formation of a quantum walk ratchet, illustrating how seemingly adverse effects can be beneficial under specific conditions. Second, we examine the open Bose-Hubbard model, representing a true many-body system interacting not only with its environment but also internally. This introduces significant complexity making the analysis of large interacting systems numerically infeasible. To address These challenges, we discuss the truncated Wigner method and aim to extend this methodology beyond ist typical approximations.
The connection between these two studies lies in their open nature and their common experimental implementation in optical lattices: The atom optics kicked rotor describes non-interacting atoms, where each atom interacts with the environment but not with each other, while the Bose-Hubbard model deals with a true many-particle system, requiring a different analytical approach. This dual investigation enhances our understanding of dissipation in open quantum systems, improving our ability to model and interpret complex quantum phenomena under realistic conditions, such as decoherence, dissipation, and particle loss.
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Topological phases and symmetries in 1D quantum walks (Bachelor Thesis)
Abstract
Recently [Phys. Rev. Lett., 121:070402, Aug 2018] a quantum kicked rotor walk has been implemented in momentum space by loading a 87Rb Bose-Einstein condensate into an optical pulsed lattice. The experimental results showed overall good agreement with the theoretical predictions but also differed in the details. A complementary argument to previous explanations will be given, consulting light shift induced effects and dispersive properties of the system for causing the observed discrepancies. Furthermore, from the field of mathematics topological principles have been passed on to physics. For example the quantum hall effect can be understood in terms of Chern numbers as topological invariant. It has been recognized that periodically driven quantum systems have the capacity to resolve the unconventional topological matter. The double kicked quantum rotor with internal spin 1/2 degree of freedom is such a system, displaying a connection between topologically protected edge states and the topologically invariant winding number.
The mean chiral displacement is an experimentally obtainable observable that converges onto the winding number. This offers interesting possibilities for measuring topological phase transition. Recognizing These possibilities, investigations regarding the feasibility will be presented, suggesting a new protocol for an experimental implementation.