Reducibility of 1-D Quantum Harmonic Oscillator with Decaying Conditions on the Derivative of Perturbation Potentials

We prove the reducibility of 1-D quantum harmonic oscillators in $\mathbb R$ perturbed by a quasi-periodic in time potential $V(x,ωt)$ under the following conditions, namely there is a $C>0$ such that \begin{equation*} |V(x,θ)|\le C,\quad|x\partial_xV(x,θ)|\le C,\quad\forall~(x,θ)\in\mathbb R\times\mathbb T_σ^n. \end{equation*} The corresponding perturbation matrix $(P_i^j(θ))$ is proved to satisfy $(1+|i-j|)| P_i^j(θ)|\le C$ and $\sqrt{ij}|P_{i+1}^{j+1}(θ)-P_i^j(θ)|\le C$ for any $θ\in\mathbb T_σ^n$ and $i,j\geq 1$. A new reducibility theorem is set up under this kind of decay in the perturbation matrix element $P_{i}^j(θ)$ as well as the discrete difference matrix element $P_{i+1}^{j+1}(θ)-P_i^j(θ)$. For the proof the novelty is that we use the decay in the discrete difference matrix element to control the measure estimates for the thrown parameter sets.

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