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Search Results: 1 - 10 of 198225 matches for " N. Regnault "
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Entanglement Spectroscopy and its Application to the Quantum Hall Effects
N. Regnault
Physics , 2015,
Abstract: The entanglement spectroscopy, initially introduced by Li and Haldane in the context of the fractional quantum Hall effects, has stimulated an extensive range of studies. The entanglement spectrum is the spectrum of the reduced density matrix, when we partition the system into two. For many quantum systems, it unveils a unique feature: Computed from the bulk ground state wave function, the entanglement spectrum give access to the physics of edge excitations. Using this property, the entanglement spectroscopy has proved to be a highly valuable tool to diagnose topological ordering. These lectures intend to provide an overview of the entanglement spectroscopy, mainly in the context of the fractional quantum Hall effect. We introduce the basic concepts through the case of the quantum spin chains. We discuss the connection with the entanglement entropy and the matrix product state representation. We show how the entanglement spectrum can be computed for non-interacting topological phases and how it reveals the edge excitation from the ground state. We then present an extensive review of the entanglement spectra applied to the fractional quantum Hall phases, showing how much information is encoded within the ground state and how different partitions probe different type of excitations. Finally, we discuss the application of this tool to study the fractional Chern insulators.
Quantum Hall fractions in rotating Bose-Einstein condensates
N. Regnault,Th. Jolicoeur
Physics , 2002, DOI: 10.1103/PhysRevLett.91.030402
Abstract: We study the Quantum Hall phases that appear in the dilute limit of rotating Bose-Einstein condensates. By exact diagonalization in a spherical geometry we obtain the ground-state and low-lying excited states of a small number of bosons as a function of the filling fraction nu, ratio of the number of bosons to the number of vortices. We show the occurrence of the Jain principal sequence of incompressible liquids for nu = 1/2, 2/3, 3/4, 4/3, 5/4 as well as the Pfaffian state for nu =1. The collective excitations for the Jain sequence are well described by a composite-fermion scheme.
The structure of spinful quantum Hall states: a squeezing perspective
E. Ardonne,N. Regnault
Physics , 2011, DOI: 10.1103/PhysRevB.84.205134
Abstract: We provide a set of rules to define several spinful quantum Hall model states. The method extends the one known for spin polarized states. It is achieved by specifying an undressed root partition, a squeezing procedure and rules to dress the configurations with spin. It applies to both the excitation-less state and the quasihole states. In particular, we show that the naive generalization where one preserves the spin information during the squeezing sequence, may fail. We give numerous examples such as the Halperin states, the non-abelian spin-singlet states or the spin-charge separated states. The squeezing procedure for the series (k=2,r) of spinless quantum Hall states, which vanish as r powers when k+1 particles coincide, is generalized to the spinful case. As an application of our method, we show that the counting observed in the particle entanglement spectrum of several spinful states matches the one obtained through the root partitions and our rules. This counting also matches the counting of quasihole states of the corresponding model Hamiltonians, when the latter is available.
Microscopic model for the boson integer quantum Hall effect
N. Regnault,T. Senthil
Physics , 2013, DOI: 10.1103/PhysRevB.88.161106
Abstract: In two dimensions strongly interacting bosons in a magnetic field can form an integer quantum Hall state. This state has a bulk gap, no fractional charges or topological order in the bulk but nevertheless has quantized Hall transport and symmetry protected edge excitations. Here we study a simple microscopic model for such a state in a system of two component bosons in a strong orbital magnetic field. We show through exact diagonalization calculations that the model supports the boson integer quantum Hall ground state in a range of parameters.
Poisson algebra of 2d dimensionally reduced gravity
D. Bernard,N. Regnault
Physics , 2000, DOI: 10.1088/1126-6708/2000/05/017
Abstract: Using a Lax pair based on twisted affine $sl(2,R)$ Kac-Moody and Virasoro algebras, we deduce a r-matrix formulation of two dimensional reduced vacuum Einstein's equations. Whereas the fundamental Poisson brackets are non-ultralocal, they lead to pure c-number modified Yang-Baxter equations. We also describe how to obtain classical observables by imposing reasonable boundaries conditions.
Quantum Hall fractions in ultracold atomic vapors
N. Regnault,Th. Jolicoeur
Physics , 2004, DOI: 10.1142/S0217984904007530
Abstract: Atomic vapors can be prepared and manipulated at very low densities and temperatures. When they are rotating, they can reach a quantum Hall regime in which there should be manifestations of the fractional quantum Hall effect. We discuss the appearance of the principal sequence of fractions nu =p/(p+- 1) for bosonic atoms. The termination point of this series is the paired Moore-Read Pfaffian state. Exotic states fill the gap between the paired state and the vortex lattice expected at high filling of the lowest Landau level. In fermionic vapors, the p-wave scattering typical of ultralow energy collisions leads to the hard-core model when restricted to the lowest Landau level.
Parafermionic states in rotating Bose-Einstein condensates
N. Regnault,Th. Jolicoeur
Physics , 2006, DOI: 10.1103/PhysRevB.76.235324
Abstract: We investigate possible parafermionic states in rapidly rotating ultracold bosonic atomic gases at lowest Landau level filling factor nu=k/2. We study how the system size and interactions act upon the overlap between the true ground state and a candidate Read-Rezayi state. We also consider the quasihole states which are expected to display non-Abelian statistics. We numerically evaluate the degeneracy of these states and show agreement with a formula given by E. Ardonne. We compute the overlaps between low-lying exact eigenstates and quasihole candidate wavefunctions. We discuss the validity of the parafermion description as a function of the filling factor.
Floquet Thermalization: Symmetries and Random Matrix Ensembles
N. Regnault,Rahul Nandkishore
Physics , 2015,
Abstract: We investigate the role of symmetries in determining the random matrix class describing quantum thermalization in a periodically driven many body quantum system. Using a combination of analytical arguments and numerical exact diagonalization, we establish that a periodically driven `Floquet' system can be in a different random matrix class to the instantaneous Hamiltonian. A periodically driven system can thermalize even when the instantaneous Hamiltonian is integrable. A Floquet system that thermalizes in general can display integrable behavior at commensurate driving frequencies. When the instantaneous Hamiltonian and Floquet operator both thermalize, the Floquet problem can be in the unitary class while the instantaneous Hamiltonian is always in the orthogonal class, and vice versa. We extract general principles regarding when a Floquet problem can thermalize to a different symmetry class to the instantaneous Hamiltonian. A (finite-sized) Floquet system can even display crossovers between different random matrix classes as a function of driving frequency.
The Anatomy of Abelian and Non-Abelian Fractional Quantum Hall States
B. Andrei Bernevig,N. Regnault
Physics , 2009, DOI: 10.1103/PhysRevLett.103.206801
Abstract: We deduce a new set of symmetries and relations between the coefficients of the expansion of Abelian and Non-Abelian Fractional Quantum Hall (FQH) states in free (bosonic or fermionic) many-body states. Our rules allow to build an approximation of a FQH model state with an overlap increasing with growing system size (that may sometimes reach unity!) while using a fraction of the original Hilbert space. We prove these symmetries by deriving a previously unknown recursion formula for all the coefficients of the Slater expansion of the Laughlin, Read Rezayi and many other states (all Jacks multiplied by Vandermonde determinants), which completely removes the current need for diagonalization procedures.
Analysis of a SU(4) generalization of Halperin's wave function as an approach towards a SU(4) fractional quantum Hall effect in graphene sheets
M. O. Goerbig,N. Regnault
Physics , 2007, DOI: 10.1103/PhysRevB.75.241405
Abstract: Inspired by the four-fold spin-valley symmetry of relativistic electrons in graphene, we investigate a possible SU(4) fractional quantum Hall effect, which may also arise in bilayer semiconductor quantum Hall systems with small Zeeman gap. SU(4) generalizations of Halperin's wave functions [Helv. Phys. Acta 56, 75 (1983)], which may break differently the original SU(4) symmetry, are studied analytically and compared, at nu=2/3, to exact-diagonalization studies.
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