15 January 2018 Spectral asymptotics for sub-Riemannian Laplacians, I: Quantum ergodicity and quantum limits in the 3-dimensional contact case
Yves Colin de Verdière, Luc Hillairet, Emmanuel Trélat
Duke Math. J. 167(1): 109-174 (15 January 2018). DOI: 10.1215/00127094-2017-0037


This is the first paper of a series in which we plan to study spectral asymptotics for sub-Riemannian (sR) Laplacians and to extend results that are classical in the Riemannian case concerning Weyl measures, quantum limits, quantum ergodicity, quasimodes, and trace formulae. Even if hypoelliptic operators have been well studied from the point of view of PDEs, global geometrical and dynamical aspects have not been the subject of much attention. As we will see, already in the simplest case, the statements of the results in the sR setting are quite different from those in the Riemannian one.

Let us consider an sR metric on a closed 3-dimensional manifold with an oriented contact distribution. There exists a privileged choice of the contact form, with an associated Reeb vector field and a canonical volume form that coincides with the Popp measure. We establish a quantum ergodicity (QE) theorem for the eigenfunctions of any associated sR Laplacian under the assumption that the Reeb flow is ergodic. The limit measure is given by the normalized Popp measure.

This is the first time that such a result is established for a hypoelliptic operator, whereas the usual Shnirelman theorem yields QE for the Laplace–Beltrami operator on a closed Riemannian manifold with ergodic geodesic flow.

To prove our theorem, we first establish a microlocal Weyl law, which allows us to identify the limit measure and to prove the microlocal concentration of the eigenfunctions on the characteristic manifold of the sR Laplacian. Then, we derive a Birkhoff normal form along this characteristic manifold, thus showing that, in some sense, all 3-dimensional contact structures are microlocally equivalent. The quantum version of this normal form provides a useful microlocal factorization of the sR Laplacian. Using the normal form, the factorization, and the ergodicity assumption, we finally establish a variance estimate, from which QE follows.

We also obtain a second result, which is valid without any ergodicity assumption: every quantum limit (QL) can be decomposed in a sum of two mutually singular measures: the first measure is supported on the unit cotangent bundle and is invariant under the sR geodesic flow, and the second measure is supported on the characteristic manifold of the sR Laplacian and is invariant under the lift of the Reeb flow. Moreover, we prove that the first measure is zero for most QLs.


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Yves Colin de Verdière. Luc Hillairet. Emmanuel Trélat. "Spectral asymptotics for sub-Riemannian Laplacians, I: Quantum ergodicity and quantum limits in the 3-dimensional contact case." Duke Math. J. 167 (1) 109 - 174, 15 January 2018. https://doi.org/10.1215/00127094-2017-0037


Received: 17 September 2015; Revised: 15 May 2017; Published: 15 January 2018
First available in Project Euclid: 10 November 2017

zbMATH: 06847243
MathSciNet: MR3743700
Digital Object Identifier: 10.1215/00127094-2017-0037

Primary: 35P20
Secondary: 53D10 , 53D25

Keywords: contact manifolds , quantum ergodicity , sub-Riemannian Laplacian

Rights: Copyright © 2018 Duke University Press


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Vol.167 • No. 1 • 15 January 2018
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