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J. E. Avron

Publications and source records attributed to J. E. Avron.

50 records · Page 3Linked to original sources
arXiv2000

Born-Oppenheimer Approximation near Level Crossing

We consider the Born-Oppenheimer problem near conical intersection in two dimensions. For energies close to the crossing energy we describe the wave function near an isotropic crossing and show that it is related to generalized hypergeometric functions 0F3. This function is to a conical intersection what the Airy function is to a classical turning point. As an application we calculate the anomalous Zeeman shift of vibrational levels near a crossing.

quant-ph↗
arXiv1999

Smooth adiabatic evolutions with leaky power tails

Adiabatic evolutions with a gap condition have, under a range of circumstances, exponentially small tails that describe the leaking out of the spectral subspace. Adiabatic evolutions without a gap condition do not seem to have this feature in general. This is a known fact for eigenvalue crossing. We show that this is also the case for eigenvalues at the threshold of the continuous spectrum by considering the Friedrichs model.

quant-ph↗
arXiv1999

Adiabatic Theorem without a Gap Condition

We prove the adiabatic theorem for quantum evolution without the traditional gap condition. All that this adiabatic theorem needs is a (piecewise) twice differentiable finite dimensional spectral projection. The result implies that the adiabatic theorem holds for the ground state of atoms in quantized radiation field. The general result we prove gives no information on the rate at which the adiabatic limit is approached. With additional spectral information one can also estimate this rate.

math-ph↗
arXiv1999

Quantum Transport in Molecular Rings and Chains

We study charge transport driven by deformations in molecular rings and chains. Level crossings and the associated Longuet-Higgins phase play a central role in this theory. In molecular rings a vanishing cycle of shears pinching a gap closure leads, generically, to diverging charge transport around the ring. We call such behavior homeopathic. In an infinite chain such a cycle leads to integral charge transport which is independent of the strength of deformation. In the Jahn-Teller model of a planar molecular ring there is a distinguished cycle in the space of uniform shears which keeps the molecule in its manifold of ground states and pinches level crossing. The charge transport in this cycle gives information on the derivative of the hopping amplitudes.

math-ph↗
arXiv1998

An Adiabatic Theorem without a Gap Condition: Two level system coupled to quantized radiation field

We prove an adiabatic theorem for the ground state of the Dicke model in a slowly rotating magnetic field and show that for weak electron-photon coupling, the adiabatic time scale is close to the time scale of the corresponding two level system--without the quantized radiation field. There is a correction to this time scale which is the Lamb shift of the model. The photon field affect the rate of approach to the adiabatic limit through a logarithmic correction originating from an infrared singularity characteristic of QED.

math.FA↗
arXiv1998

The Longuet-Higgins Phase and Charge Transport in Molecular Rings

The Longuet-Higgins-Berry's phase has remarkable consequences for charge transport in molecular rings. For generic (conical) crossing, where the phase is $π$, a vanishing cause can lead to a diverging response in the amount of charge transport. Away from level crossings, when the phase is 0, a vanishing cause leads to a vanishing response. The divergence of the response near crossing is related to, but distinct from, the divergence that occurs in the generalized susceptibility. We illustrate this behavior for quantum models of molecular rings driven by a running wave of small amplitude at zero and finite temperatures.

cond-mat↗
arXiv1998

Odd Viscosity

When time reversal is broken the viscosity tensor can have a non vanishing odd part. In two dimensions, and only then, such odd viscosity is compatible with isotropy. Elementary and basic features of odd viscosity are examined by considering solutions of the wave and Navier-Stokes equations for hypothetical fluids where the stress is dominated by odd viscosity.

physics.flu-dyn↗
arXiv1997

Geometric Forces on Point Fluxes in Quantum Hall Fluids

We study the forces that act on a point flux carrying an integral number of flux units in quantum Hall fluids. Forces due to external fields, Lorentz and Magnus type forces, and the forces due to mutual interaction of point fluxes are considered. The forces are related to the adiabatic curvature associated with families of Landau Hamiltonians. The problem displays distinct features of the quantum Hall fluids with point fluxes on the plane and on the torus, which, however, agree at the thermodynamic limit.

cond-mat.mes-hall↗
arXiv1996

Boundary Conditions for Bulk and Edge States in Quantum Hall Systems

For two dimensional Schroedinger Hamiltonians we formulate boundary conditions that split the Hilbert space according to the chirality of the eigenstates on the boundary. With magnetic fields, and in particular, for Quantum Hall Systems, this splitting corresponds to edge and bulk states. Applications to the integer and fractional Hall effect and some open problems are described.

cond-mat.mes-hall↗
arXiv1996

Piezoelectricity: Quantized Charge Transport Driven by Adiabatic Deformations

We study the (zero temperature) quantum piezoelectric response of Harper-like models with broken inversion symmetry. The charge transport in these models is related to topological invariants (Chern numbers). We show that there are arbitrarily small periodic modulations of the atomic positions that lead to nonzero charge transport for the electrons.

cond-mat↗
arXiv1995

Viscosity of Quantum Hall Fluids

The viscosity of quantum fluids with an energy gap at zero temperature is non-dissipative and is related to the adiabatic curvature on the space of flat background metrics (which plays the role of the parameter space). For a quantum Hall fluid on two dimensional tori this viscosity is computed. In this case the average viscosity is quantized and is proportional to the total magnetic flux through the torus.

cond-mat↗
arXiv1994

Adiabatic Quantum Transport: Quantization and Fluctuations

Quillen's local index theorem is used to study the charge transport coefficients (adiabatic curvature) associated to the ground state of a Schrödinger operator for a charged (spinless) particle on a closed, multiply connected surface. The formula splits the adiabatic curvature into an explicit integral part and a fluctuating part which has a natural interpretation in terms of quantum chaos.

hep-lat↗