The entropy threshold conjecture for cat-map quantum limits

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Let A∈SL(2,Z)A\in SL(2,\mathbb{Z}) be a hyperbolic cat map, let μ\mu be a quantum limit for AA, let ord⁡N(A)\operatorname{ord}_N(A) be the order of AA modulo NN, and let hmaxh_{\mathrm{max}} denote the maximal entropy. Suppose that

lim inf⁡N→∞ord⁡N(A)log⁡N≥C.\liminf_{N\to\infty}\frac{\operatorname{ord}_N(A)}{\log N}\geq C.

Entropy threshold conjecture. The entropy of μ\mu satisfies

h(μ)≥hmax−1C.h(\mu)\geq h_{\mathrm{max}}-\frac{1}{C}.

In particular, if

lim inf⁡N→∞ord⁡N(A)log⁡N=∞,\liminf_{N\to\infty}\frac{\operatorname{ord}_N(A)}{\log N}=\infty,

then μ\mu is Lebesgue measure.

This conjecture predicts the transition from the logarithmic-scale non-QUE examples for cat maps to QUE just beyond that scale. It would improve the known QUE results at polynomial propagator-order scales and quantify how short periods constrain entropy.

References

Primary source

Shimon Brooks, “Logarithmic-scale Quasimodes that do not Equidistribute”, arXiv:1303.2484 (2013).

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