Session M7: Quantum Control of Electronic and Nuclear Dynamics

Control of the two-Photon Double Ionization of Helium with Intense Chirped Attosecond Laser Pulses

We study the two-photon double ionization process of the helium atom by solving numerically the nonrelativistic time-dependent Schr\"{o}dinger equation in its full dimensionality. We investigate with an intense chirped attosecond laser pulse of central carrier frequency that corresponds to the 29th harmonic of a Ti-sapphire laser the direct and sequential processes in helium. We show how it is possible by adjusting the chirp parameter to control the dominance of one process over the other within the atom. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.   

Using Ultrafast Pulse Shaping to Probe Electronic Interference in Strong Field Ionization

We make use of shaped ultrafast laser pulses, velocity map imaging and coincidence detection to study electron dynamics in Strong Field Ionization (SFI) of small molecules. In particular, we consider the role of interference between different pathways during ionization. In one experiment, the molecule is ionized with a phase locked pulse pair. We study the ionization yield as a function of the delay and the relative phase between pulses, and interpret its variation in terms of strong field laser molecule phase matching.   

Polarization-Dependent Measurements of Molecular Super Rotors with Oriented Angular Momenta

Controlling molecular motion would enable manipulation of energy flow between molecules. Here we have used an optical centrifuge to investigate energy transfer between molecular super rotors with oriented angular momenta. The polarizable electron cloud of the molecules interacts with the electric field of linearly polarized light that angularly accelerates over the time of the optical pulse. This process drives molecules into high angular momentum states that are oriented with the optical field and have energies far from equilibrium. High resolution transient IR spectroscopy reveals the dynamics of collisional energy transfer for these super excited rotors. The results of this study leads to a more fundamental understanding of energy balance in non-equilibrium environments and the physical and chemical properties of gases in a new regime of energy states. Results will be presented for several super rotor species including carbon monoxide, carbon dioxide, and acetylene. Polarization-dependent measurements reveal the extent to which the super rotors maintain spatial orientation of high angular momentum states.   

Optimization of a laser pulse for xuv Raman excitation of neon using quantum control combined with multichannel electronic structure

We present a combined quantum control and electronic structure technique for optimizing laser pulses. Krotov's method of control which monotonically improves a given cost function is combined with the multichannel time-dependent configuration interaction singles (TDCIS) method [Greenman, et. al. PRA 82, 023406 (2010)]. We apply this technique to optimize an xuv laser pulse to perform the Raman excitation of Ne to the $1s^22s^22p^53p$ state through the intermediate resonance $1s^22s^12p^63p$ state. Quantum control is useful to minimize ionization and population of other states in this process.   

Quantum Control of Molecular Gas Hydrodynamics

We report quantum control of rotational energy absorption in diatomic molecular gases such as N$_{2}$ and O$_{2}$, and in general any molecule with anisotropic polarizability. A sequence of non-ionizing ultra-short laser pulses tuned to the rotational revival period coherently excites a molecular wavepacket to high j-states. Over a $\sim$ 100 ps timescale, the energy stored in the rotational ensemble repartitions into translational degrees of freedom, impulsively heating the gas. The gas density response is measured interferometrically and sonographically as a proxy for the rotational energy deposited. Furthermore, if the second of two pulses arrives at the rotational half revival period, the wavepacket is de-excited before thermalization, strongly suppressing gas heating. Adjusting the pulse sequence energy and timing allows detailed control of the hydrodynamic response, enabling applications in air density patterning including high power air waveguides lasting for milliseconds [1, 2]. \\[4pt] [1] N. Jhajj, E. W. Rosenthal, R. Birnbaum, J. K. Wahlstrand, and H. M. Milchberg, accepted, PRX.\\[0pt] [2] Y.-H. Cheng, J. K. Wahlstrand, N. Jhajj, and H. M. Milchberg, Opt. Express \textbf{21}, 4740 (2013).   

Ultrafast Quantum Control and Quantum Processing in the Vibronic States of Molecules and Solids

The unusual features of quantum mechanics are enabling the development of technologies not possible with classical physics, including applications in secure communications, quantum processing, and enhanced measurement. Efforts to build these devices utilize nonclassical states in numerous quantum systems, including cavity quantum electrodynamics, trap ions, nuclear spins, \textit{etc}. as the basis for many prototypes. Here we investigate vibronic states in both molecules and bulk solids as distinct alternatives. We demonstrate a memory for light based on storing photons in the vibrations of hydrogen molecules and the optical phonons of diamond. Both classical [1,2] and nonclassical [3] photon states are used. These THz-bandwidth memories can be used to store femtosecond pulses for many operational time bins before the states decohere, making them viable for local photonic processing. We investigate decoherence and major sources of competing noise. While sustaining quantum coherence is critical for most quantum processing, rapid dephasing can also be used as a resource in these systems for rapid quantum random number generation, suitable for high-performance cryptography [4,5]. [1] Bustard, P. J., \textit{et al}. Phys. Rev. Lett., 111(8). (2013). [2] England, D. G., \textit{et al}. Phys. Rev. Lett., 111(24). (2013) [3] \textit{In preparation} [4] Bustard, P. J., \textit{et al}. Opt. Express, 21(24), 29350-29357. (2011). [5] England, D. G., \textit{et al}. Appl. Phys. Lett. \textit{Accepted.} (2014)   

Carrier-envelope phase dependences of D$_2$ dissociation into Rydberg deuterium fragments

Control via the carrier-envelope phase (CEP) has been observed experimentally as asymmetries in the molecular dissociation direction, and more rarely as oscillations in the dissociation yield. A general theory of CEP dependences attributes these oscillations to interference of dissociation pathways involving a different net number of photons [1]. The laser-induced dissociation of D$_2$ provides an excellent test bed for the generality of this theory. Our measurements of long-lived D* fragments exhibit strong oscillations of the asymmetry and yield with CEP in both low- and high-energy dissociation. As predicted, the periodicity shows 1-photon difference in the asymmetry and 2-photon difference in the yield. Moreover, at some dissociation energies we can identify smaller contributions from interfering dissociation paths with a larger net photon-number difference. \\[4pt] [1] V. Roudnev and B. D. Esry, Phys. Rev. Lett. {\bf 99}, 220406 (2007)   

Carrier-envelope phase control over the branching ratios in strong-field dissociation of HD$^{+}$

We have theoretically explored the carrier-envelope phase (CEP) effect on the dissociation of HD$^{+}$ with short, intense laser pulses. The branching ratios (BR) of the dissociating fragments are calculated for several laser wavelengths ranging from 800 nm to 4000 nm with two-cycle pulse durations. The CEP dependence of the BR is shown to be stronger with increasing wavelength. In addition, we explore the feasibility of CEP control over the BR with relatively long pulses by exploiting the dynamics of the nonadiabatic coupling which has a strong dependence on the internuclear distance and energy of the dissociating wave packet.   

Dressed state analysis of population inversion in a 4-level system comprised of hyperfine states in Rb interacting with a single nanosecond, chirped pulse

Ultracold alkali atoms have been conventionally used for quantum operations. In the previous work, a semiclassical model of a single pulse interacting with the hyperfine states of $5S_{1/2}$ and $5P_{1/2,3/2}$ in Rb is presented revealing quantum control parameters that provide population inversion within $5S_{1/2}$. Here, to understand the mechanism of two-photon adiabatic passage induced by a single narrow-band pulse, we analyze the dressed state picture in the four-level system. We also perform a comparative analysis with a three-level $\Lambda$ system that works as a good approximation within a ceratin range of parameters. We study the dressed states evolution when the key field parameters, the peak Rabi frequency, the chirp rate and the pulse duration, induce both the adiabatic and nonadiabatic regime of light-matter interaction. The analysis reveals the mediating role of the excited state manifold in adiabatic passage.