Demonstration of Turnstiles as a Chaotic Ionization Mechanism in Rydberg Atoms

Abstract

We present an experimental and theoretical study of the chaotic ionization of quasi-onedimensional potassium Rydberg wavepackets via a phase-space turnstile mechanism. Turnstiles form a general transport mechanism for numerous chaotic systems, and this study explicitly illuminates their relevance to atomic ionization. We create time-dependent Rydberg wavepackets, subject them to alternating applied electric-field "kicks", and measure the electron survival probability. Ionization depends not only on the initial electron energy, but also on the phase-space position of the electron with respect to the turnstile -that part of the electron packet inside the turnstile ionizes after the applied ionization sequence, while that part outside the turnstile does not. The survival data thus encode information on the geometry and location of the turnstile, and are in good agreement with theoretical predictions.

Invariant manifolds and the geometry of front propagation in fluid flows

“…The passive advection of particles in a twodimensional fluid flow is a well-studied problem important both for its direct relevance to fluid mixing and for its broader connection to Hamiltonian dynamics. The latter finds applications ranging from chaotic ionization in atomic physics [1][2][3][4][5][6][7] to the motion of asteroids in the solar system 8 . A key observation in passive chaotic advection is that particular curves-the invariant manifolds-form barriers to particle transport [9][10][11][12] .…”

Chaotic ionization of a stationary electron state via a phase space turnstile

“…Such systems span a broad range of length scales and include global weather patterns [3], mixing of fluids [4][5][6], and firing of neurons [7]. One mesoscale system that has been used recently to study nonlinear dynamics and chaos is the kicked Rydberg atom [8][9][10][11], i.e., a high-n atomic state that is subject to a series of electric field pulses [termed half-cycle pulses (HCPs)] with durations τ k T n , where T n is the electron Kepler period. In this regime, each HCP simply delivers an impulsive momentum transfer, or "kick," to the excited electron given by p = F(t)dt, where F(t) is the force exerted on the electron as a result of the applied HCP.…”

“…This paper focuses on the geometric structures present in the phase space of a Rydberg atom subject to external electric field pulses of alternating sign, i.e., alternating between kicks toward and away from the nucleus. Earlier work indicated that ionization in this system is controlled by a geometric structure of phase space called a turnstile, which promotes electrons from bound to ionized states during one kicking cycle [10,12]. (For another example of turnstile-mediated ionization, see…”

“…The important role played by the turnstile in chaotic ionization was highlighted in a recent series of experiments using quasi-1D, n ∼ 306 and n ∼ 350, Rydberg atoms in which an HCP was used to create an electronic wave packet that exhibited transient localization in phase space [10]. By controlling the overlap between the wave packet and the turnstile, it was shown that when the overlap was large, a sizable fraction of the Rydberg atoms was ionized, whereas when the overlap was small, the majority of atoms survived.…”

“…In the present work, we demonstrate a more direct test of the turnstile's role; an initial quasi-1D stationary Rydberg state is employed. Furthermore, unlike [10] in which only the duration of the kicking cycle was varied, here we vary both the duration and the kick strength. Varying the kick strength allows us to probe the transition from no ionization to more than 50% ionization.…”