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Ögren, M. & Kavoulakis, G. M. (2025). Yrast states of quantum droplets confined in a ring potential. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 111(1), Article ID 013305.
Open this publication in new window or tab >>Yrast states of quantum droplets confined in a ring potential
2025 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 111, no 1, article id 013305Article in journal (Refereed) Published
Abstract [en]

We consider a quantum droplet which is confined in a ring potential. We investigate the so-called yrast state,i.e., the lowest-energy state of the droplet assuming that it has some fixed expectation value of the angularmomentum. Two of the most interesting aspects of this problem are the nonlinear term—which is partly attractive and partly repulsive—and the periodic boundary conditions. For some range of the parameters, the attractive or the repulsive part of the nonlinear term dominates and one gets the expected behavior. In some intermediate regime, the two nonlinear terms are of comparable size. In this case, both the solution and the corresponding dispersion relation show an interesting behavior. Finally, we make contact with the problem of solitary-wave excitation since the derived solutions are traveling-wave, i.e., solitary-wave, solutions.

Place, publisher, year, edition, pages
American Physical Society, 2025
Keywords
quantum droplets, vortices, yrast states
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-118002 (URN)10.1103/PhysRevA.111.013305 (DOI)001414541200019 ()2-s2.0-85214365940 (Scopus ID)
Available from: 2025-01-06 Created: 2025-01-06 Last updated: 2025-03-04Bibliographically approved
Abdullaev, F. K., Yuldashev, J. S. & Ögren, M. (2024). Dynamical stabilization of two-dimensional vector solitons under nonlinearity management. In: The International Conference on Theoretical Physics and New Technologies: Proceedings. Paper presented at The International Conference on Theoretical Physics and New Technologies (ICTPT-2024), Samarkand, Uzbekistan, September 30 - October 4, 2024 (pp. 42-42).
Open this publication in new window or tab >>Dynamical stabilization of two-dimensional vector solitons under nonlinearity management
2024 (English)In: The International Conference on Theoretical Physics and New Technologies: Proceedings, 2024, p. 42-42Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Periodic variations in dispersion and nonlinearity are key tools for studying nonlinear wave processes in optics and quantum gases. These variations have led to the dynamical stabilization of BEC (preventing collapse), soliton stabilization in BEC with spin-orbit coupling and stable two-dimensional NLSE solitons and compactons [1]. Most studies focus on dynamical stabilization in scalar two-dimensional cubic NLSE and one-dimensional NLSE with quintic nonlinearities, though collapse phenomena also occur in N-coupled NLSE. For vector two-dimensional NLSE, dynamical stabilization via nonlinearity management has been primarily explored through numerical simulations [2]. This work aims to develop a theoretical analysis of dynamical stabilization of solitons in two-dimensional vector NLSE under strong nonlinearity management.

Keywords
solitons, non-linear management, dynamical stabilization
National Category
Other Mathematics
Identifiers
urn:nbn:se:oru:diva-119077 (URN)
Conference
The International Conference on Theoretical Physics and New Technologies (ICTPT-2024), Samarkand, Uzbekistan, September 30 - October 4, 2024
Available from: 2025-02-04 Created: 2025-02-04 Last updated: 2025-02-05Bibliographically approved
Nikolaou, S., Kavoulakis, G. M. & Ögren, M. (2024). Rapidly rotating quantum droplets confined in a harmonic potential. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 110(4), Article ID 043302.
Open this publication in new window or tab >>Rapidly rotating quantum droplets confined in a harmonic potential
2024 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 110, no 4, article id 043302Article in journal (Refereed) Published
Abstract [en]

We consider a “symmetric” quantum droplet in two spatial dimensions, which rotates in a harmonic potential, focusing mostly on the limit of “rapid” rotation. We examine this problem using a purely numerical approach, as well as a semianalytic Wigner-Seitz approximation (first developed by Baym, Pethick, and their co-workers) for the description of the state with a vortex lattice. Within this approximation we assume that each vortex occupies a cylindrical cell, with the vortex-core size treated as a variational parameter. Working with a fixed angular momentum, as the angular momentum increases and depending on the atom number, the droplet accommodates none, few, or many vortices, before it turns to center-of-mass excitation. For the case of a “large” droplet, working with a fixed rotational frequency of the trap Ω, as Ω approaches the trap frequency 𝜔, a vortex lattice forms, the number of vortices increases, the mean spacing between them decreases, while the “size” of each vortex increases as compared to the size of each cell. In contrast to the well-known problem of contact interactions, where we have melting of the vortex lattice and highly correlated many-body states, here no melting of the vortex lattice is present, even when Ω=𝜔. This difference is due to the fact that the droplet is self-bound. For Ω=𝜔, the “smoothed” density distribution becomes a flat top, very much like the static unconfined droplet. When Ω exceeds 𝜔, the droplet maintains its shape and escapes to infinity, via center-of-mass motion.

Place, publisher, year, edition, pages
American Physical Society, 2024
Keywords
quantum droplets, vortex lattice, rapid rotation
National Category
Atom and Molecular Physics and Optics
Research subject
Mathematics; Physics
Identifiers
urn:nbn:se:oru:diva-116540 (URN)10.1103/PhysRevA.110.043302 (DOI)001334483900004 ()2-s2.0-85206218808 (Scopus ID)
Note

S.N. acknowledges support from the Hellenic Foundation for Research and Innovation (HFRI) under the 5th Call for HFRI PhD Fellowships.

Available from: 2024-10-04 Created: 2024-10-04 Last updated: 2024-11-01Bibliographically approved
Nikolaou, S., Kavoulakis, G. M. & Ögren, M. (2024). Rotating quantum droplets confined in an anharmonic potential. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 109, Article ID 043304.
Open this publication in new window or tab >>Rotating quantum droplets confined in an anharmonic potential
2024 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 109, article id 043304Article in journal (Refereed) Published
Abstract [en]

We investigate the rotational properties of quantum droplets, which form in a mixture of two Bose-Einstein condensates, in the presence of an anharmonic trapping potential. We identify various phases as the atom number and the angular momentum or angular velocity of the trap vary. These phases include center-of-mass–like excitation (without or with vortices), vortices of single and multiple quantization, etc. Finally, we compare our results with those of the single-component problem.

Place, publisher, year, edition, pages
American Physical Society, 2024
Keywords
quantum droplets, vortices, center-of-mass–like excitation
National Category
Atom and Molecular Physics and Optics
Research subject
Physics; Mathematics
Identifiers
urn:nbn:se:oru:diva-112841 (URN)10.1103/PhysRevA.109.043304 (DOI)001222320000008 ()2-s2.0-85189324973 (Scopus ID)
Available from: 2024-04-03 Created: 2024-04-03 Last updated: 2024-05-29Bibliographically approved
Rousse, F., Fasi, M., Dmytryshyn, A., Gulliksson, M. & Ögren, M. (2024). Simulations of quantum dynamics with fermionic phase-space representations using numerical matrix factorizations as stochastic gauges. Journal of Physics A: Mathematical and Theoretical, 57(1), Article ID 015303.
Open this publication in new window or tab >>Simulations of quantum dynamics with fermionic phase-space representations using numerical matrix factorizations as stochastic gauges
Show others...
2024 (English)In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 57, no 1, article id 015303Article in journal (Refereed) Published
Abstract [en]

The Gaussian phase-space representation can be used to implement quantum dynamics for fermionic particles numerically. To improve numerical results, we explore the use of dynamical diffusion gauges in such implementations. This is achieved by benchmarking quantum dynamics of few-body systems against independent exact solutions. A diffusion gauge is implemented here as a so-called noise-matrix, which satisfies a matrix equation defined by the corresponding Fokker-Planck equation of the phase-space representation. For the physical systems with fermionic particles considered here, the numerical evaluation of the new diffusion gauges allows us to double the practical simulation time, compared with hitherto known analytic noise-matrices. This development may have far reaching consequences for future quantum dynamical simulations of many-body systems. 

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2024
Keywords
phase-space representations, quantum dynamics, diffusion gauges
National Category
Computational Mathematics Condensed Matter Physics
Research subject
Mathematics; Physics
Identifiers
urn:nbn:se:oru:diva-110059 (URN)10.1088/1751-8121/ad0e2b (DOI)001113350500001 ()2-s2.0-85180071987 (Scopus ID)
Funder
Carl Tryggers foundation , CTS 19:431Wenner-Gren Foundations, UPD 2019-0067Swedish Research Council, 2021-05393
Available from: 2023-12-05 Created: 2023-12-05 Last updated: 2024-02-05Bibliographically approved
Rousse, F., Eriksson, O. & Ögren, M. (2023). Correlated quantum dynamics of graphene clusters. Physical Review B, 107(13), Article ID 134306.
Open this publication in new window or tab >>Correlated quantum dynamics of graphene clusters
2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 13, article id 134306Article in journal (Refereed) Published
Abstract [en]

Phase-space representations are a family of methods for dynamics of both bosonic , fermionic systems, that work by mapping the system's density matrix to a quasiprobability density and the Liouville-von Neumann equation of the Hamiltonian to a corresponding density differential equation for the probability. We investigate here the accuracy and the computational efficiency of one approximate phase-space representation, called the fermionic truncated Wigner approximation (fTWA), applied to the Fermi-Hubbard model. On a many-body 2D system, with hopping strength and Coulomb U tuned to represent the electronic structure of graphene, the method is found to be able to capture the time evolution of first-order (site occupation) and second-order (correlation functions) moments significantly better than the mean-field, Hartree-Fock method. The fTWA was also compared to results from the exact diagonalization method for smaller systems , in general the agreement was found to be good. The fully parallel computational requirement of fTWA scales in the same order as the Hartree-Fock method, and the largest system considered here contained 198 lattice sites.

Place, publisher, year, edition, pages
American Physical Society, 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:oru:diva-105997 (URN)10.1103/PhysRevB.107.134306 (DOI)000975822800004 ()2-s2.0-85158840901 (Scopus ID)
Funder
Carl Tryggers foundation Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy AgencyeSSENCE - An eScience CollaborationEuropean Commission, 854843
Available from: 2023-05-22 Created: 2023-05-22 Last updated: 2024-03-18Bibliographically approved
Abdullaev, F. K., Yuldashev, J. S. & Ögren, M. (2023). Management of solitons in medium with competing cubic and quadratic nonlinearities. Optik (Stuttgart), 274, Article ID 170545.
Open this publication in new window or tab >>Management of solitons in medium with competing cubic and quadratic nonlinearities
2023 (English)In: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 274, article id 170545Article in journal (Refereed) Published
Abstract [en]

Management of solitons in media with competing quadratic and cubic nonlinearities is investigated. Two schemes, using rapid modulations of a mismatch parameter, and of the Kerr nonlinearity parameter are studied. For both cases, the averaged in time wave equations are derived. In the case of mismatch management, the region of the parameters where stabilization is possible is found. In the case of Kerr nonlinearity management, it is shown that the effective chi(2) nonlinearity depends on the intensity imbalance between fundamental (FH) and second (SH) harmonics. Predictions obtained from the averaged equations are confirmed by numerical simulations of the full PDE’s.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Solitons, Mismatch management, Kerr nonlinearity management, Competing nonlinearities
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-103206 (URN)10.1016/j.ijleo.2023.170545 (DOI)000989150500001 ()2-s2.0-85146415593 (Scopus ID)
Funder
Örebro University
Note

Funding agency:

State budget of the Republic of Uzbekistan

Available from: 2023-01-17 Created: 2023-01-17 Last updated: 2023-06-01Bibliographically approved
Abdullaev, F. K., Yuldashev, J. S. & Ögren, M. (2023). Nonlinearity managed vector solitons. Physics Letters A, 491, Article ID 129206.
Open this publication in new window or tab >>Nonlinearity managed vector solitons
2023 (English)In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 491, article id 129206Article in journal (Refereed) Published
Abstract [en]

The evolution of vector solitons under nonlinearity management is studied. The averaged over strong and rapid modulations in time of the inter-species interactions vector Gross-Pitaevskii equation (GPE) is derived. The averaging gives the appearance of the effective nonlinear quantum pressure depending on the population of the other component. Using this system of equations, the existence and stability of the vector solitons under the action of the strong nonlinearity management (NM) is investigated. Using a variational approach the parameters of NM vector solitons are found. The numerical simulations of the full time-dependent coupled GPE confirms the theoretical predictions. 

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Vector solitons, Nonlinearity management, Variational approach
National Category
Atom and Molecular Physics and Optics
Research subject
Physics; Mathematics
Identifiers
urn:nbn:se:oru:diva-110057 (URN)10.1016/j.physleta.2023.129206 (DOI)001110859600001 ()2-s2.0-85176143616 (Scopus ID)
Funder
Örebro University
Available from: 2023-12-05 Created: 2023-12-05 Last updated: 2023-12-15Bibliographically approved
Nepal, S., Ögren, M., Wondmagegne, Y. & Muntean, A. (2023). Random walks and moving boundaries: Estimating the penetration of diffusants into dense rubbers. Probabilistic Engineering Mechanics, 74, Article ID 103546.
Open this publication in new window or tab >>Random walks and moving boundaries: Estimating the penetration of diffusants into dense rubbers
2023 (English)In: Probabilistic Engineering Mechanics, ISSN 0266-8920, E-ISSN 1878-4275, Vol. 74, article id 103546Article in journal (Refereed) Published
Abstract [en]

For certain materials science scenarios arising in rubber technology, one-dimensional moving boundary problems with kinetic boundary conditions are capable of unveiling the large-time behavior of the diffusants penetration front, giving a direct estimate on the service life of the material. Driven by our interest in estimating how a finite number of diffusant molecules penetrate through a dense rubber, we propose a random walk algorithm to approximate numerically both the concentration profile and the location of the sharp penetration front. The proposed scheme decouples the target evolution system in two steps: (i) the ordinary differential equation corresponding to the evaluation of the speed of the moving boundary is solved via an explicit Euler method, and (ii) the associated diffusion problem is solved by a random walk method. To verify the correctness of our random walk algorithm we compare the resulting approximations to computational results based on a suitable finite element approach with a controlled convergence rate. Our numerical results recover well penetration depth measurements of a controlled experiment designed specifically for this setting.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Moving boundary problem with kinetic condition, Explicit Euler method, Random walk approx., Finite element approx.
National Category
Computational Mathematics Textile, Rubber and Polymeric Materials
Research subject
Mathematics
Identifiers
urn:nbn:se:oru:diva-110056 (URN)10.1016/j.probengmech.2023.103546 (DOI)001108952000001 ()2-s2.0-85175365511 (Scopus ID)
Funder
Swedish Research Council, VR 2018-03648Knowledge Foundation, 2019-0213 2020-015
Available from: 2023-12-05 Created: 2023-12-05 Last updated: 2023-12-11Bibliographically approved
Nikolaou, S., Kavoulakis, G. M. & Ögren, M. (2023). Rotating quantum droplets confined in a harmonic potential. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 108(5), Article ID 053309.
Open this publication in new window or tab >>Rotating quantum droplets confined in a harmonic potential
2023 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 108, no 5, article id 053309Article in journal (Refereed) Published
Abstract [en]

We investigate the rotational properties of a two-component, two-dimensional self-bound quantum droplet, which is confined in a harmonic potential and compare them with the well-known problem of a single-component atomic gas with contact interactions. For a fixed value of the trap frequency, choosing some representative values of the atom number, we determine the lowest-energy state, as the angular momentum increases. For a sufficiently small number of atoms, the angular momentum is carried via center-of-mass excitation. For larger values, when the angular momentum is sufficiently small, we observe vortex excitation instead. Depending on the actual atom number, one or more vortices enter the droplet. Beyond some critical value of the angular momentum, however, the droplet does not accommodate more vortices and the additional angular momentum is carried via center-of-mass excitation in a "mixed" state. Finally, the excitation spectrum is also briefly discussed. 

Place, publisher, year, edition, pages
American Physical Society, 2023
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-110058 (URN)10.1103/physreva.108.053309 (DOI)001110834300008 ()2-s2.0-85177615823 (Scopus ID)
Available from: 2023-12-05 Created: 2023-12-05 Last updated: 2024-01-10Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-2630-7479

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