| 1. |
- Ardonne, Eddy, et al.
(författare)
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Degeneracy of non-Abelian quantum Hall states on the torus : domain walls and conformal field theory
- 2008
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Ingår i: Journal of Statistical Mechanics. - 1742-5468. ; , s. P04016-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the non-Abelian Read–Rezayi quantum Hall states on the torus, where it is natural to employ a mapping of the many-body problem onto a one-dimensional lattice model. On the thin torus—the Tao–Thouless (TT) limit—the interacting many-body problem is exactly solvable. The Read–Rezayi states at filling ν = k/(kM+2) are known to be exact ground states of a local repulsive k+1-body interaction, and in the TT limit this is manifested in that all states in the ground state manifold have exactly k particles on any kM+2 consecutive sites. For M \neq 0 the two-body correlations of these states also imply that there is no more than one particle on M adjacent sites. The fractionally charged quasiparticles and quasiholes appear as domain walls between the ground states, and we show that the number of distinct domain wall patterns gives rise to the nontrivial degeneracies, required by the non-Abelian statistics of these states. In the second part of the paper we consider the quasihole degeneracies from a conformal field theory (CFT) perspective, and show that the counting of the domain wall patterns maps one to one on the CFT counting via the fusion rules. Moreover we extend the CFT analysis to topologies of higher genus
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| 2. |
- Bergholtz, E. J., et al.
(författare)
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Pfaffian quantum Hall state made simple : Multiple vacua and domain walls on a thin torus
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:8, s. 081308-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the Moore-Read Pfaffian state on a thin torus. The known sixfold degeneracy is realized by two inequivalent crystalline states with a four- and twofold degeneracy, respectively. The fundamental quasihole and quasiparticle excitations are domain walls between these vacua, and simple counting arguments give a Hilbert space of dimension 2n−1 for 2n−k holes and k particles at fixed positions and assign each a charge ±e∕4. This generalizes the known properties of the hole excitations in the Pfaffian state as deduced using conformal field theory techniques. Numerical calculations using a model Hamiltonian and a small number of particles support the presence of a stable phase with degenerate vacua and quarter-charged domain walls also away from the thin-torus limit. A spin-chain Hamiltonian encodes the degenerate vacua and the various domain walls.
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| 3. |
- Fischer, Sara, et al.
(författare)
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Intracranial volume is normal in infants with sagittal synostosis.
- 2015
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Ingår i: Journal of plastic surgery and hand surgery. - 2000-6764. ; 49:1, s. 62-64
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Premature sagittal synostosis results in an elongated, narrow skull shape, scaphocephaly. It has been unclear whether the intracranial volume (ICV) of these children is different from that of normal children. The aim of the present study was to precisely determine the ICV in a large cohort of children with premature sagittal synostosis and to compare it to the ICV of a sex- and age-matched control group. All patients (n = 143) with isolated sagittal synostosis registered in the Göteborg Craniofacial Registry until the end of 2012 with a preoperative CT examination were identified. For each case, a sex- and age- (±30 days) matched control was identified from children who had undergone CT for post-traumatic or neurological reasons. The ICV was measured in a semi-automatic MATLAB program with functions such as region growing, watershed, and thresholding in axial CT slices. The ICV was calculated using the Cavalieri principle. The mean (± SEM) values of ICV for children with sagittal synostosis and for corresponding controls were 866 ± 13 ml and 870 ± 15 ml, respectively. The mean ages of these groups were 173 ± 8 days and 172 ± 8 days, respectively. Subgroup analysis of sex and age at CT (≤180 days and >180 days) did not reveal any differences in ICV between cases and controls. Precise determination of ICV in addition to the use of adequate controls has made it possible to conclude that children with premature isolated sagittal synostosis have a normal ICV.
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| 4. |
- Maltese, Giovanni, 1974, et al.
(författare)
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Intracranial volume before and after surgical treatment for isolated metopic synostosis.
- 2014
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Ingår i: The Journal of craniofacial surgery. - 1536-3732. ; 25:1, s. 262-266
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Tidskriftsartikel (refereegranskat)abstract
- Metopic synostosis results in a keel-shaped forehead, hypotelorism, and an increased interparietal width. This study aimed to measure the frontal and total intracranial volume in patients with metopic synostosis before and after surgery and to compare the effect of 2 different operation methods. All patients operated for isolated metopic synostosis between 2002 and 2008 at Sahlgrenska University Hospital who had undergone preoperative and/or postoperative computed tomographic examination (at 3 y of age) were included. The patients were grouped according to operation method: (1) forehead remodeling in combination with a bone graft or (2) forehead remodeling in combination with a spring. Sex- and age-matched controls were identified. A previously developed MATLAB computer program was used to measure the frontal and total intracranial volumes. Sixty patients and 198 controls were included. Preoperatively, the patients with metopic synostosis had significantly lower frontal volumes than those of the controls (P < 0.001) but equal total intracranial volumes. The operations redistributed the intracranial volume and resulted in an improved, frontal-total intracranial volume ratio. However, at 3 years of age, the frontal volume (P < 0.001), total intracranial volume (P ≤ 0.002), and ratio between the 2 (P < 0.001) were significantly lower in the patients than in the controls. The 2 operation methods were equally efficient in creating an improved frontal-total ratio. Surgery for metopic synostosis improves the distribution of the intracranial volume but does not result in normal total intracranial volume or frontal volume at 3 years of age.
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| 5. |
- Tovetjärn, Robert, 1982, et al.
(författare)
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Intracranial volume in 15 children with bilateral coronal craniosynostosis.
- 2014
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Ingår i: Plastic and reconstructive surgery. Global open. - 2169-7574. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Intracranial volume (ICV) growth in patients with bilateral coronal craniosynostosis (BCS) is not well described. It is therefore important to evaluate the consequences of cranial surgery in children with this condition. The aim of the present study was to evaluate ICVs in patients operated on for BCS.
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| 6. |
- Wikberg, Emma, 1982-, et al.
(författare)
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Fractional domain walls from on-site softening in dipolar bosons
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 033607-
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Tidskriftsartikel (refereegranskat)abstract
- We study dipolar bosons in a 1D optical lattice and identify a region in parameter space-strong coupling but relatively weak on-site repulsion-hosting a series of stable charge-density-wave (CDW) states whose low-energy excitations, built from fractional domain walls, have remarkable similarities to those of non-Abelian fractional quantum Hall states. Here, a conventional domain wall between translated CDW's may be split by inserting strings of degenerate, but inequivalent, CDW states. Outside these insulating regions, we find numerous supersolids as well as a superfluid regime. The mentioned phases should be accessible experimentally and, in particular, the fractional domain walls can be created in the ground state using single-site addressing, i.e., by locally changing the chemical potential.
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| 7. |
- Wikberg, Emma, 1982-
(författare)
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Non-abelian quantum Hall states and fractional charges in one dimension
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fractional quantum Hall effect has, since its discovery around 30 years ago, been a vivid field of research—both experimentally and theoretically. In this thesis we investigate certain non-abelian quantum Hall states by mapping the two-dimensional system onto a thin torus, where the problem becomes effectively one-dimensional and hopping is suppressed, meaning that the classical electrostatic interaction dominates. The approach assists with a simplified view of ground states and their degeneracies, as well as of the nature of the fractionally charged, minimal excitations of the corresponding quantum Hall states. Similar models are also relevant for cold atoms trapped in one-dimensional optical lattices, where interaction parameters are available for tuning, which opens up for realizing interesting lattice states in controllable environments. The diverse applicability of the one-dimensional electrostatic lattice hamiltonian motivates the exploration of the systems and models treated in this work.In the absence of hopping or tunneling, the low-energy behavior of the one-dimensional lattice system is ultimately dependent on the nature of the electrostatic interaction present. For ordinary interactions such as Coulomb, the ground state at particle filling fraction ν= p/q has a well-known q-fold center-of-mass degeneracy and the elementary excitations are domain walls of fractional charge e* = ±e/q. These appear in abelian quantum Hall systems and are known since earlier. In this work, we show how other types of interaction give rise to increased ground state degeneracies and, as a result, to the emergence of split fractional charges recognized from non- abelian quantum Hall systems.
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| 8. |
- Wikberg, Emma, 1982-
(författare)
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Nontrivial ground-state degeneracies and generalized fractional excitations in the 1D lattice
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study a 1D lattice Hamiltonian, relevant for a wide range of interesting physical systems like, e.g., the quantum-Hall system, cold atoms or molecules in optical lattices, and TCNQ salts. Through a tuning of the interaction parameters and a departure from a strictly convex interaction, nontrivial ground-state degeneracies and fractionally charged excitations emerge. The excitations, being a generalization of the fractional charges known from the fractional quantum-Hall effect, appear as domain walls between inequivalent ground states and carry the charge ± e/mq , where m is an integer and associated with the specified interaction, and ν = p/q is the filling fraction in the lattice. The description points at an interesting resemblance to states connected to non-Abelian statistics, which is central for the concept of topological quantum computing.
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| 9. |
- Wikberg, Emma, 1982-, et al.
(författare)
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Spin chain description of rotating bosons at v = 1
- 2009
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Ingår i: Journal of Statistical Mechanics. - 1742-5468. ; , s. P07038-
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Tidskriftsartikel (refereegranskat)abstract
- We consider bosons at Landau level filling ν = 1 on a thin torus. In analogy with previous work on fermions at filling ν = 1/2, we map the low-energy sector onto a spin-1/2 chain. While the fermionic system may realize the gapless XY phase, we show that typically this does not happen for the bosonic system. Instead, both delta function and Coulomb interaction lead to gapped phases in the bosonic system, and in particular we identify a phase corresponding to the non-Abelian Moore–Read state. In the spin language, the Hamiltonian is dominated by a ferromagnetic next-nearest-neighbor interaction, which leads to a description consistent with the non-trivial degeneracies of the ground and excited states of this phase of matter. In addition we comment on the similarities and differences of the two systems mentioned above and fermions at ν = 5/2.
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