121,763 research outputs found
Kibble-Zurek exponent and chiral transition of the period-4 phase of Rydberg chains
No full textChains of Rydberg atoms have emerged as an amazing playground to study quantum physics in 1D. Playing with inter-atomic distances and laser detuning, one can in particular explore the commensurate-incommensurate transition out of density waves through the Kibble-Zurek mechanism, and the possible presence of a chiral transition with dynamical exponent z > 1. Here, we address this problem theoretically with effective blockade models where the short-distance repulsions are replaced by a constraint of no double occupancy. For the period-4 phase, we show that there is an Ashkin-Teller transition point with exponent ν = 0.78 surrounded by a direct chiral transition with a dynamical exponent z = 1.11 and a Kibble-Zurek exponent μ = 0.41. For Rydberg atoms with a van der Waals potential, we suggest that the experimental value μ = 0.25 is due to a chiral transition with z ≃ 1.9 and ν ≃ 0.47 surrounding an Ashkin-Teller transition close to the 4-state Potts universality.QN/Chepiga La
Critical properties of the Majorana chain with competing interactions
No full textWe explore critical properties of a chain of interacting Majorana fermions, particles that are their own antiparticles. We study the combined effect of two competing interaction terms of the shortest possible range and show this results in a very rich phase diagram with nine different phases, five of which are critical. In addition, we report a wide variety of quantum phase transitions: the tri-critical Ising lines; the Lifshitz critical line characterized by the dynamical critical exponent z=3; two Kosterlitz-Thouless transitions; and an exotic first-order transition between the floating and the gapped phases. However, the most surprising result is the emergence of the commensurate line at which the floating phases collapse into direct transition. We provide numerical evidences that the resulting multicritical point belongs to the universality class of the eight-vertex model. Implications in the context of supersymmetric properties of the Majorana chain are briefly discussed. QN/Chepiga La
Supersymmetry and multicriticality in a ladder of constrained fermions
No full textSupersymmetric lattice models of constrained fermions are known to feature exotic phenomena such as superfrustration, with an extensive degeneracy of ground states, the nature of which is however generally unknown. Here we address this issue by considering a superfrustrated model, which we deform from the supersymetric point. By numerically studying its two-parameter phase diagram, we reveal a rich phenomenology. The vicinity of the supersymmetric point features period-4 and period-5 density waves which are connected by a floating phase (incommensurate Luttinger liquid) with smoothly varying density. The supersymmetric point emerges as a multicritical point between these three phases. Inside the period-4 phase we report a valence-bond solid type ground state that persists up to the supersymmetric point. Our numerical data for transitions out of density-wave phases are consistent with the Pokrovsky-Talapov universality class. Furthermore, our analysis unveiled a period-3 phase with a boundary determined by a competition between single and two-particle instabilities accompanied by a doubling of the wavevector of the density profiles along a line in the phase diagram.QN/Chepiga La
From Kosterlitz-Thouless to Pokrovsky-Talapov transitions in spinless fermions and spin chains with next-nearest-neighbor interactions
No full textWe investigate the nature of the quantum phase transition out of density-wave phase in a spinless fermion model with nearest-and next-nearest-neighbor interaction at one-Third filling. Using extensive density matrix renormalization group (DMRG) simulations, we show that the transition changes it nature. For weak next-nearest-neighbor coupling the transition is of Kosterlitz-Thouless type, in agreement with bosonisation predictions. For large next-nearest-neighbor repulsion we provide numerical evidences that the transition belongs to the Pokrovsky-Talapov univerality class describing a nonconformal commensurate-incommensurate transition. We argue that the change of the nature of the transition is a result of incommensurability induced by frustration and realized even at zero doping. The implications in the context of the XXZ chain with next-nearest-neighbor Ising interaction is briefly discussed. </p
Critical properties of quantum three- and four-state Potts models with boundaries polarized along the transverse field
No full textBy computing the low-lying energy excitation spectra with the density matrix
renormalization group algorithm we show that boundaries polarized in the
direction of the transverse field lead to scale-invariant conformal towers of
states at the critical point of the quantum four-state Potts model - a special
symmetric case of the Ashkin-Teller model. Furthermore, by direct comparison of
the excitation spectra we phenomenologically establish the duality between the
transverse-polarized and three-state-mixed boundary conditions at the
four-state Potts critical point. Finally, for completeness, we verify that in
the quantum three-state Potts model the "new" boundary conditions dual to the
mixed ones can be realized by polarizing edge spins along the transverse field.Comment: 19 pages, 7 figure
Tunable quantum criticality in multicomponent Rydberg arrays
No full textArrays of Rydberg atoms have appeared as a remarkably rich playground to
study quantum phase transitions in one dimension. One of the biggest puzzles
that was brought forward in this context are chiral phase transitions out of
density waves. Theoretically predicted chiral transition out of period-four
phase is still pending experimental verification mainly due to extremely short
interval over which this transition is realized in a single-component Rydberg
array. In this letter we show that multi-component Rydberg arrays with extra
experimentally tunable parameters provide a mechanism to manipulate quantum
critical properties without breaking translation symmetry explicitly.
We consider an effective blockade model of two component Rydberg atoms. Weak
and strong components obey nearest- and next-nearest-neighbor blockades
correspondingly. When laser detuning is applied to either of the two components
the system is in the period-3 and period-2 phases. But laser detuning applied
to both components simultaneously stabilizes the period-4 phase partly bounded
by the chiral transition. We show that relative ratio of the Rabi frequencies
of the two components tunes the properties of the conformal Ashkin-Teller point
and allows to manipulate an extent of the chiral transition. The prospects of
multi-component Rydberg arrays in the context of critical fusion is briefly
discussed.Comment: 11 pages, 14 figure
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Lifshitz point at commensurate melting of chains of Rydberg atoms
No full textThe recent investigation of chains of Rydberg atoms has brought back the problem of commensurateincommensurate transitions into the focus of current research. In two-dimensional classical systems or in one-dimensional quantum systems, the commensurate melting of a period- p phase with p larger than 4 is known to take place through an intermediate floating phase where correlations between domain walls or particles decay only as a power law, but when p is equal to 3 or 4, it has been argued by Huse and Fisher that the transition could also be direct and continuous in a nonconformal chiral universality class with a dynamical exponent larger than 1. This is only possible, however, if the floating phase terminates at a Lifshitz point before reaching the conformal point, a possibility debated since then. Here we argue that this is a generic feature of models where the number of particles is not conserved because the exponent of the floating phase changes along the Pokrovsky-Talapov transition and can, thus, reach the value at which the floating phase becomes unstable. Furthermore, we show numerically that this scenario is realized in an effective model of the period-3 phase of Rydberg chains in which hard-core bosons are created and annihilated three by three: The Luttinger liquid parameter reaches the critical value p(2)/8 = 9/8 along the Pokrovsky-Talapov transition, leading to a Lifshitz point that separates the floating phase from a chiral transition. Implications beyond Rydberg atoms are briefly discussed.CTM
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
No full textAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
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