| 1. |
- Dehkharghani, A., et al.
(författare)
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Quantum magnetism in strongly interacting one-dimensional spinor Bose systems
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Strongly interacting one-dimensional quantum systems often behave in a manner that is distinctly different from their higher-dimensional counterparts. When a particle attempts to move in a one-dimensional environment it will unavoidably have to interact and 'push' other particles in order to execute a pattern of motion, irrespective of whether the particles are fermions or bosons. A present frontier in both theory and experiment are mixed systems of different species and/or particles with multiple internal degrees of freedom. Here we consider trapped two-component bosons with short-range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated ground states with manifestly ferromagnetic wave functions. Furthermore, we predict excited states that have perfect antiferromagnetic ordering. This holds for both balanced and imbalanced systems, and we show that it is a generic feature as one crosses from few-to many-body systems.
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| 2. |
- Forssen, Christian, 1974, et al.
(författare)
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Living on the edge of stability, the limits of the nuclear landscape
- 2013
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Ingår i: Physica Scripta. - : IOP Publishing. - 1402-4896 .- 0031-8949. ; T152:T152, s. 014022-
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Tidskriftsartikel (refereegranskat)abstract
- A first-principles description of nuclear systems along the drip lines presents a substantial theoretical and computational challenge. In this paper, we discuss the nuclear theory roadmap, some of the key theoretical approaches, and present selected results with a focus on long isotopic chains. An important conclusion, which consistently emerges from these theoretical analyses, is that three-nucleon forces are crucial for both global nuclear properties and detailed nuclear structure, and that many-body correlations due to the coupling to the particle continuum are essential as one approaches particle drip lines. In the quest for a comprehensive nuclear theory, high performance computing plays a key role.
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| 3. |
- Forssen, Christian, 1974, et al.
(författare)
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Strongly Interacting Few-Fermion Systems in a Trap
- 2015
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 56:11-12, s. 837-844
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Tidskriftsartikel (refereegranskat)abstract
- Few- and many-fermion systems on the verge of stability, and consisting of strongly interacting particles, appear in many areas of physics. The theoretical modeling of such systems is a very difficult problem. In this work we present a theoretical framework that is based on the rigged Hilbert space formulation. The few-body problem is solved by exact diagonalization using a basis in which bound, resonant, and non-resonant scattering states are included on an equal footing. Current experiments with ultracold atoms offer a fascinating opportunity to study universal properties of few-body systems with a high degree of control over parameters such as the external trap geometry, the number of particles, and even the interaction strength. In particular, particles can be allowed to tunnel out of the trap by applying a magnetic-field gradient that effectively lowers the potential barrier. The result is a tunable open quantum system that allows detailed studies of the tunneling mechanism. In this Paper we introduce our method and present results for the decay rate of two distinguishable fermions in a one-dimensional trap as a function of the interaction strength. In particular, we present for the first time several technical and numerical details of our approach, recently published in Lundmark et al. (Phys Rev A 91:041601, 2015). We also show results from a careful analysis of the numerical convergence.
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| 4. |
- Johnson, Calvin W., et al.
(författare)
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White paper: From bound states to the continuum
- 2020
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 47:12
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Forskningsöversikt (refereegranskat)abstract
- This white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program ‘From bound states to the continuum: Connecting bound state calculations with scattering and reaction theory’. One of the biggest and most important frontiers in nuclear theory today is to construct better and stronger bridges between bound state calculations and calculations in the continuum, especially scattering and reaction theory, as well as teasing out the influence of the continuum on states near threshold. This is particularly challenging as many-body structure calculations typically use a bound state basis, while reaction calculations more commonly utilize few-body continuum approaches. The many-body bound state and few-body continuum methods use different language and emphasize different properties. To build better foundations for these bridges, we present an overview of several bound state and continuum methods and, where possible, point to current and possible future connections.
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| 5. |
- Kim, Youngman, et al.
(författare)
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Ab initio no core full configuration approach for light nuclei
- 2014
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Ingår i: Chiral Symmetry in Hadrons and Nuclei. - : WORLD SCIENTIFIC. - 9789814618229 ; , s. 78-85
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Comprehensive understanding of the structure and reactions of light nuclei poses theoretical and computational challenges. Still, a number of ab initio approaches have been developed to calculate the properties of atomic nuclei using fundamental interactions among nucleons. Among them, we work with the ab initio no core full configuration (NCFC) method and ab initio no core Gamow Shell Model (GSM). We first review these approaches and present some recent results.
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| 6. |
- Kim, Youngman, et al.
(författare)
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Ab initio no core full configuration approach for light nuclei
- 2014
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Ingår i: International Journal of Modern Physics E. - 0218-3013. ; 23:7, s. Article no. 1461004 -
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Tidskriftsartikel (refereegranskat)abstract
- Comprehensive understanding of the structure and reactions of light nuclei poses theoretical and computational challenges. Still, a number of ab initio approaches have been developed to calculate the properties of atomic nuclei using fundamental interactions among nucleons. Among them, we work with the ab initio no core full configuration (NCFC) method and ab initio no core Gamow Shell Model (GSM). We first review these approaches and present some recent results.
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| 7. |
- Lindgren, E. J., et al.
(författare)
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Fermionization of two-component few-fermion systems in a one-dimensional harmonic trap
- 2014
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- The nature of strongly interacting Fermi gases and magnetism is one of the most important and studied topics in condensed-matter physics. Still, there are many open questions. A central issue is under what circumstances strong short-range repulsive interactions are enough to drive magnetic correlations. Recent progress in the field of cold atomic gases allows one to address this question in very clean systems where both particle numbers, interactions and dimensionality can be tuned. Here we study fermionic few-body systems in a one dimensional harmonic trap using a new rapidly converging effective-interaction technique, plus a novel analytical approach. This allows us to calculate the properties of a single spin-down atom interacting with a number of spin-up particles, a case of much recent experimental interest. Our findings indicate that, in the strongly interacting limit, spin-up and spin-down particles want to separate in the trap, which we interpret as a microscopic precursor of one-dimensional ferromagnetism in imbalanced systems. Our predictions are directly addressable in current experiments on ultracold atomic few-body systems.
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| 8. |
- Lundmark, Rikard, 1990, et al.
(författare)
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Tunneling theory for tunable open quantum systems of ultracold atoms in one-dimensional traps
- 2015
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 91:4
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Tidskriftsartikel (refereegranskat)abstract
- The creation of tunable open quantum systems is becoming feasible in current experiments with ultracold atoms in low-dimensional traps. In particular, the high degree of experimental control over these systems allows detailed studies of tunneling dynamics, e.g., as a function of the trapping geometry and the interparticle interaction strength. In order to address this exciting opportunity we present a theoretical framework for two-body tunneling based on the rigged Hilbert space formulation. In this approach, bound, resonant, and scattering states are included on an equal footing and we argue that the coupling of all these components is vital for a correct description of the relevant threshold phenomena. In particular, we study the tunneling mechanism for two-body systems in one-dimensional traps and different interaction regimes. We find a strong dominance of sequential tunneling of single particles for repulsive and weakly attractive systems, while there is a signature of correlated pair tunneling in the calculated many-particle flux for strongly attractive interparticle interaction.
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| 9. |
- Papadimitriou, G., et al.
(författare)
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Ab initio no-core Gamow shell model calculations with realistic interactions
- 2013
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 88:4
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Tidskriftsartikel (refereegranskat)abstract
- No-core Gamow shell model (NCGSM) is applied to study selected well-bound and unbound states of helium isotopes. This model is formulated on the complex energy plane and, by using a complete Berggren ensemble, treats bound, resonant, and scattering states on equal footing. We use the density matrix renormalization group method to solve the many-body Schrodinger equation. To test the validity of our approach, we benchmarked the NCGSM results against Faddeev and Faddeev-Yakubovsky exact calculations for H-3 and He-4 nuclei. We also performed ab initio NCGSM calculations for the unstable nucleus He-5 and determined the ground-state energy and decay width, starting from a realistic (NLO)-L-3 chiral interaction.
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| 10. |
- Papadimitriou, G., et al.
(författare)
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The No core gamow shell model for ab-initio nuclear structure calculations
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 66
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Konferensbidrag (refereegranskat)abstract
- We apply the Berggren basis in a No-Core Shell Model framework to calculate ground state (g.s.) energies of 3H, 4He and 5He. In our studies we use the Argonne υ18 and the chiral N3LO potentials, both of which are renormalized via a V low-k process. © Owned by the authors, published by EDP Sciences, 2014.
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| 11. |
- Rotureau, Jimmy, 1976, et al.
(författare)
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Effective Field Theory and the Gamow Shell Model: The 6He Halo Nucleus
- 2013
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 54:5-6, s. 725-735
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Tidskriftsartikel (refereegranskat)abstract
- We combine halo/cluster effective field theory (H/CEFT) and the Gamow shell model (GSM) to describe the 0+ ground state of 6He as a three-body halo system. We use two-body interactions for the neutron-alpha particle and two-neutron pairs obtained from H/CEFT at leading order, with parameters determined from scattering in the p3/2 and s0 channels, respectively. The three-body dynamics of the system is solved using the GSM formalism, where the continuum states are incorporated in the shell model valence space. We find that in the absence of three-body forces the system collapses, since the binding energy of the ground state diverges as cutoffs are increased. We show that addition at leading order of a three-body force with a single parameter is sufficient for proper renormalization and to fix the binding energy to its experimental value.
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| 12. |
- Rotureau, Jimmy, 1976
(författare)
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Effective Field Theory for Few Particles in a Trap
- 2013
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 54:5-6, s. 635-645
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution we show applications of effective field theory (EFT) to few-particle systems trapped in a harmonic oscillator potential. The principles of EFT allows to construct interactions among the particles in a systematic and improvable manner. We first consider systems of two-component fermions and show excellent agreements with the exact solution at unitarity (for the two- and three-body problem) and results obtained by other methods (in the four-body case). We then consider trapped systems of three nucleons and extract neutron–deuteron phase shifts, and show that the quartet scattering length is in good agreement with experimental data. We also show the collapse of the system in the J π = 1/2+, T = 1/2 (triton) channel at Leading-Order when no three-nucleon force is included.
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| 13. |
- Rotureau, Jimmy, 1976
(författare)
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Interaction for the trapped fermi gas from a unitary transformation of the exact two-body spectrum
- 2013
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6079 .- 1434-6060. ; 67:7
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Tidskriftsartikel (refereegranskat)abstract
- We study systems of few two-component fermions interacting in a Harmonic Oscillator trap. The fermion-fermion interaction is generated in a finite basis with a unitary transformation of the exact two-body spectrum given by the Busch formula. The few-body Schrodinger equation is solved with the formalism of the No-Core Shell Model. We present results for a system of three fermions interacting at unitarity as well as for finite values of the S-wave scattering length a(2) and effective range r(2). Unitary systems with four and five fermions are also considered. We show that the many-body energies obtained in this approach are in excellent agreement with exact solutions for the three-body problem, and results obtained by other methods in the other cases.
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| 14. |
- Rotureau, Jimmy, 1976, et al.
(författare)
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Two and three nucleons in a trap, and the continuum limit
- 2012
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 85:3
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Tidskriftsartikel (refereegranskat)abstract
- We describe systems of two and three nucleons trapped in a harmonic-oscillator potential with interactions from the pionless effective field theory up to next-to-leading order (NLO). We construct the two-nucleon interaction using two-nucleon scattering information. We calculate the trapped levels in the three-nucleon system with isospin T = 1/2 and determine the three-nucleon force needed for stability of the triton. We extract neutron-deuteron phase shifts, and show that the quartet scattering length is in good agreement with experimental data.
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| 15. |
- Shin, Ik Jae, et al.
(författare)
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Ab initio no-core solutions for Li-6
- 2017
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 44:7
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Tidskriftsartikel (refereegranskat)abstract
- We solve for properties of Li-6 in the ab initio no-core full configuration (NCFC) approach and we separately solve for its ground state and J(pi) = 2(2)(+) resonance with the Gamow shell model (GSM) in the Berggren basis. We employ both the JISP16 and chiral NNLOopt realistic nucleon-nucleon interactions and investigate the ground state energy, excitation energies, point proton root mean square (rms) radius and a suite of electroweak observables. We also extend and test methods to extrapolate the ground state energy, point proton rms radius, and electric quadrupole moment. We attain improved estimates of these observables in the NCFC approach by using basis spaces up through N-max = 18 that enable more definitive comparisons with experiment. Using the density matrix renormalization group approach with the JISP16 interaction, we find that we can significantly improve the convergence of the GSM treatment of the Li-6 ground state and J(pi) = 2(2)(+) resonance by adopting a natural orbital single-particle basis.
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| 16. |
- Stetcu, I., et al.
(författare)
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Effective interactions and operators in the no-core shell model
- 2013
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Ingår i: Progress in Particle and Nuclear Physics. - : Elsevier BV. - 0146-6410. ; 69:1, s. 182-224
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Forskningsöversikt (refereegranskat)abstract
- Solutions to the nuclear many-body problem rely on effective interactions, and in general effective operators, to take into account effects not included in calculations. These include effects due to the truncation to finite model spaces where a numerical calculation is tractable, as well as physical terms not included in the description in the first place. In the no-core shell model (NCSM) framework, we discuss two approaches to the effective interactions based on (i) unitary transformations and (ii) effective field theory (EFT) principles. Starting from a given Hamiltonian, the unitary transformation approach is designed to take into account effects induced by the truncation to finite model spaces in which a numerical calculation is performed. This approach was widely applied to the description of nuclear properties of light nuclei; we review the theory and present representative results. In the EFT approach, a Hamiltonian is always constructed in a truncated model space according to the symmetries of the underlying theory, making use of power counting to limit the number of interactions included in the calculations. Hence, physical terms not explicitly included in the calculation are treated on the same footing with the truncation to a finite model space. In this approach, we review results for both nuclear and trapped atomic systems, for which the effective theories are formally similar, albeit describing different underlying physics. Finally, the application of the EFT method of constructing effective interactions to the Gamow shell model is briefly discussed.
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