Bertrand Girard

Visualizing Picometric Quantum Ripples of Ultrafast Wave-Packet Interference

Interference fringes in vibrating molecules are a signature of quantum mechanics, but are often so short-lived and closely spaced that they elude visualization. We have experimentally visualized dynamical quantum interferences, which appear and disappear in less than 100 femtoseconds in the iodine molecule synchronously with the periodic crossing of two counterpropagating nuclear wave packets. The obtained images have picometer and femtosecond spatiotemporal resolution, representing a detailed picture of the quantum interference.

Temporal coherent control in the photoionization of Cs2: Theory and experiment

Two identical femtosecond pulses are used to create a coherent superposition of two vibrational wave packets in a bound electronic state of cesium dimers. The oscillations of these two wave packets are further detected after photoionization of the system. Quantum interferences between the two wave packets result in a temporal coherent control of the ionization probability. The interferogram exhibits the following features as a function of the time delay between the two laser pulses: high-frequency oscillation corresponding to Ramsey fringes (at the Bohr frequency of the transition) modulated by a slow envelope corresponding to the oscillations of vibrational wave packets (vibrational recurrences). Here the control parameter is the time delay between the two laser pulses which can be used to control the preparation of a wave packet in a quantum system and monitor its evolution. The detailed theory of this experiment is presented and compared with the pump-probe experiment. The temporal coherent control exp...

One-color coherent control in Cs2. Observation of 2.7 fs beats in the ionization signal

Abstract We present the theory of one-color coherent control with two identical time-delayed laser pulses and the experimental observation of the resulting wave packet interferences in the B 1 Π u state of Cs 2 . The B state population is detected by two-photon ionization. The wave packet interference produces beats in the Cs 2 + ion signal at the optical frequency, i.e. with a period of 2.7 fs which are resolved for the first time. These beats are modulated by the vibrational recurrences and allow a determination of the vibrational period. Furthermore, we show that such interferences can be observed even when the probe step involves an electronic state parallel to the excited state in which the wave packet oscillates.

Observation of Coherent Transients in Ultrashort Chirped Excitation of an Undamped Two-Level System

The effects of coherent excitation of a two-level system with a linearly chirped pulse are studied theoretically and experimentally [in Rb (5s-5p)] in the low field regime. The coherent transients are measured directly on the excited state population on an ultrashort time scale. A sharp step corresponds to the passage through resonance. It is followed by oscillations resulting from interferences between off-resonant and resonant contributions. We finally show the equivalence between this experiment and Fresnel diffraction by a sharp edge.

Quantum State Measurement Using Coherent Transients

We present the principle and experimental demonstration of time resolved quantum state holography. The quantum state of an excited state interacting with an ultrashort chirped laser pulse is measured during this interaction. This has been obtained by manipulating coherent transients created by the interaction of femtosecond shaped pulses and rubidium atoms.

Competition of different ionization pathways in K2 studied by ultrafast pump–probe spectroscopy: A comparison between theory and experiment

We present a comparison of experiment and theory of ultrafast one-color pump–probe multiphoton ionization spectrocopy of K2. The wave packet propagation in the A 1Σu+ state and in the (2) 1Πg Rydberg state is monitored in detail by changing systematically the pump and probe wavelength from 779 nm to 837 nm. The measured total ionization rates as a function of the delay time between pump and probe are shown to depend sensitively on the pump and probe wavelengths used and exhibit drastic changes and a variety of fascinating structures as the direct observation of inward and outward wave packet detection and frequency doubling of the detected wave packet oscillation. The time dependent quantum mechanical wave packet calculations are in excellent agreement with the experimental results and allow a clear interpretation of different ionization pathways and mechanisms observed in the femtosecond ion signal.

AOPDF-shaped optical parametric amplifier output in the visible

Time shaping of ultra-short visible pulses has been performed using a specially designed acousto-optic programmable dispersive filter of 50% efficiency at the output of a two-stage non-collinear optical parametric amplifier. The set-up is compact and reliable. It provides a tunable shaped source in the visible with unique features: a 4-ps shaping window with preserved tunability over 500–650 nm, and pulses as short as 30 fs. Several-μJ output energy is easily obtained.

Factorization of numbers with Gauss sums: I. Mathematical background

We use the periodicity properties of generalized Gauss sums to factor numbers. Moreover, we derive rules for finding the factors and illustrate this factorization scheme for various examples. This algorithm relies solely on interference and scales exponentially.

RELATIVISTIC CALCULATION OF THE ELECTRONIC STRUCTURE OF THE IF MOLECULE

The electronic structure of IF is investigated using ab initio pseudopotentials and a variational/perturbative MRCI scheme (CIPSI/CIPSO). All the valence states dissociating into neutral asymptotes I(2P1/2,2P3/2)+F(2P1/2,2P3/2) and ionic asymptotes I+(3P2,3P1,3P0,1D2,1S0) +F−(1S0) are determined up to the region where they undergo avoided crossing with the neutral excited states dissociating into I*+F. The spectroscopic properties are derived and discussed in comparison with the available experimental results, with emphasis on the X, B, E, A, β, A′, and D′ states.

Factorization of numbers with Gauss sums: II. Suggestions for implementation with chirped laser pulses

We propose three implementations of the Gauss sum factorization schemes discussed in part I of this series (Wolk et al 2011 New J. Phys. 13 103007): (i) a two-photon transition in a multi-level ladder system induced by a chirped laser pulse, (ii) a chirped one-photon transition in a two-level atom with a periodically modulated excited state and (iii) a linearly chirped one-photon transition driven by a sequence of ultrashort pulses. For each of these quantum systems, we show that the excitation probability amplitude is given by an appropriate Gauss sum. We provide rules on how to encode the number N to be factored in our system and how to identify the factors of N in the fluorescence signal of the excited state.