Vibrationally highly excited trilobite molecules stabilized by nonadiabatic coupling

We report on the observation of highly excited ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>ν</a:mi> <a:mo>∼</a:mo> <a:mn>100</a:mn> <a:mo>)</a:mo> </a:mrow> </a:math> vibrational states of a trilobite ultralong-range Rydberg molecule in <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mmultiscripts> <b:mi>Rb</b:mi> <b:mprescripts/> <b:none/> <b:mn>87</b:mn> </b:mmultiscripts> </b:math> . These states manifest spectroscopically in a regularly spaced series of peaks red-detuned from the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mn>25</c:mn> <c:msub> <c:mi>f</c:mi> <c:mrow> <c:mn>7</c:mn> <c:mo>/</c:mo> <c:mn>2</c:mn> </c:mrow> </c:msub> </c:mrow> </c:math> dissociation threshold. The existence and observed stability of these states require the almost complete suppression of the adiabatic decay pathway induced by the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>P</d:mi> </d:math> -wave shape resonance of Rb. This stabilization is predicted to occur only for certain Rydberg levels where the avoided crossing between trilobite and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>P</e:mi> </e:math> -wave-dominated butterfly potential energy curves nearly vanishes, allowing the vibrational states to diabatically traverse the crossing with almost unit probability. This is the first direct measurement of beyond-Born-Oppenheimer physics in long-range Rydberg molecules, and paves the way for future experiments to access and manipulate wave packets formed from high-lying vibrational states.