Optical Control of the Rotational Angular Momentum of a Molecular Rydberg Wave Packet

Abstract

An intuitive scheme for controlling the rotational quantum state of a Rydberg molecule is demonstrated experimentally. We determine the accumulated phase difference between the various components of a molecular electron wave packet, and then employ a sequence of phase-locked optical pulses to selectively enhance or depopulate specific rotational states. The angular momentum composition of the resulting wave packet, and the efficiency of the control scheme, is determined by calculating the multipulse response of the time-dependent Rydberg populations. DOI: 10.1103/PhysRevLett.91.243601 PACS numbers: 33.80.Rv Coherent control experiments in molecular systems have tended to employ complex waveforms [1][2][3][4] generated by feedback-controlled learning loops [5]. Despite the fact that they can be remarkably effective even in complex molecules [1][2][3]6] and biological systems [3], they are not intuitive and so it is difficult to unravel the underlying physics [6]. It is extremely tempting to try to control molecular processes from first principles and recognize the control mechanism. Ideal laboratories for the design of logical control schemes are Rydberg wave packets, since the phase parameters are readily determined. The relative phases of the interfering pathways are important since optical control processes rely on the interferences between different excitation pathways. Previous experiments controlling the dynamics of Rydberg electron wave packets have focused on simple atomic systems. Phase-shaped pulses have been employed to excite arbitrary wave packets [7] and to fully characterize their amplitude and phase profile [8][9][10]. Intuitive schemes exploiting trains of phase-locked optical pulses have been employed to create Schrö dinger's cat states [11], to demonstrate Young's double slit interference in an atom [12], to control electronic orbital angular momentum [13], and the radial distribution [14]. In this Letter, we take a step further and develop an intuitive scheme to control the dynamics of a molecular system. We explore the dynamics of a molecular electron wave packet composed predominantly of two Rydberg series belonging to two different rotational quantum states of the molecular ion. We determine the accumulated phase difference and deduce an intuitive pulse sequence to obtain full control over the time-dependent populations of the rotational quantum state of the wave packet.First, consider a wave packet composed of a superposition of two noninteracting Rydberg series, with different orbital angular momenta l and quantum defects l , converging to the same ionization limit. Such a wave packet may be considered as being composed of two separate components and is written r; t nl a nl nl r exp ÿi! nl t , where nl r is the radial wave function of the eigenstate jnli, ! nl ÿ1=2 n ÿ l 2 is its frequency and a nl is its amplitude in the superposition. After an integer number of orbit periods k, each wave packet, corresponding to a channel l, accumulates a phase 2 k l , resulting in an accumulated ph...

A spectroscopic investigation of the ionisation and dissociation decay dynamics of Rydberg states of NO

“…Higher in energy near −330 cm −1 , the relative proximity of the 19p(0) and 18f(2) states results in a peak in the ionisation channel occurring at a broad plateau in the dissociation spectra. In this region there are also broad, intense features attributable to the nd(1) and ns (1) states. imately interleaved, and as such there is little interaction between the two series.…”

“…The np (2) states are found to be weak, or disappear entirely, over the range n = 27-45 where they sit on the high-energy side of members of the p(0) series. One possible explanation for this is that the decay pathways via the p(0) and p(2) states interfere with one another and (2), ns (1) and nf(2) series from least squares fitting of Equation (1) to the experimental data. this interference (constructive or destructive) is dependent on the relative energy separation and position.…”

“…It is tempting to consider this in terms of constructive interference in the dissociation channel and destructive interference in the ionisation channel although the exact mechanism is not clear. Figure 4(c) covers the energy range where the 28p(0) and 29p(0) peaks are approximately resonant with the weaker nd(1), ns (1) and np (2) states. The effect of the extra states is dramatic -the intensity of the 28p(0) and 29p(0) states in the usually dominant dissociation channel is almost entirely removed and almost all of the population appears to decay through the ionisation channel.…”

“…In our own group, we have studied the intermediate Rydberg states of NO, with principal quantum number n = 25-35 in static and ramped external fields [32][33][34]. We have also investigated the dynamics of Rydberg electron wave packets in NO [35][36][37] and demonstrated that it is possible to control the composition of the wave packet by employing phase-locked pairs of optical pulses [1,2].…”

“…The dynamics of competing ionisation and dissociation decay paths in Rydberg states of diatomic molecules attract considerable interest, not only as model systems for the investigation of competing non-radiative processes in larger molecules, but also as prototypes for coherent control [1][2][3][4]. Despite possessing only a single molecular bond, diatomic Rydberg molecules possess many of the characteristics of complex molecular systems, such as strong non-adiabatic couplings between electronic and nuclear motion, energy flow between different degrees of freedom (electronic, vibrational and rotational), delicately balanced interference effects between competing non-radiative decay pathways, complex resonances and internal time-scales spanning orders of magnitude.…”