Dynamically assisted tunneling in the Floquet picture

We study how tunneling through a potential barrier <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>V</a:mi><a:mo>(</a:mo><a:mi>x</a:mi><a:mo>)</a:mo></a:mrow></a:math> can be enhanced by an additional harmonically oscillating electric field <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mi mathvariant="fraktur">E</b:mi><b:mrow><b:mo>(</b:mo><b:mi>t</b:mi><b:mo>)</b:mo></b:mrow><b:mo>=</b:mo><b:msub><b:mi mathvariant="fraktur">E</b:mi><b:mn>0</b:mn></b:msub><b:mo form="prefix">cos</b:mo><b:mrow><b:mo>(</b:mo><b:mi>ω</b:mi><b:mi>t</b:mi><b:mo>)</b:mo></b:mrow></b:mrow></b:math> or a similar oscillating force. To this end, we transform into the Kramers-Henneberger frame and calculate the coupled Floquet channels numerically. We find distinct signatures of resonances when the incident energy <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mi>E</f:mi></f:math> equals the driving frequency <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi>ω</g:mi><g:mo>=</g:mo><g:mi>E</g:mi></g:mrow></g:math>, which clearly shows the breakdown of the time-averaged potential approximation in this regime. As a simple model for experimental applications (e.g., in solid-state physics), we study the rectangular potential, which can also be benchmarked with respect to analytical results. Finally, we consider the truncated Coulomb potential relevant for nuclear fusion. Published by the American Physical Society 2024