Coherent control of N-level quantum systems with shaped electromagnetic pulses

Stephen D. Clow

In this thesis, we present work on coherent control of multilevelquantum systems in the strong field limit using shaped ultrafastlaser pulses. In recent years there have been numerous multiphotonabsorption experiments in two,three, and four-level atomic/molecularsystems and many are performed in the limit of weak fields whereperturbation theory is valid. Here, we describe a series ofexperiments aimed at exploring and understanding multiphotontransitions when the exciting field is strong and perturbationtheory breaks down. Our approach to strong field control utilizesboth parameterized scans of various pulse shapes and closed-looplearning control to identify a pulse shape that is optimal forpopulating a target quantum state. With this we will highlight thedifference between sequential population transfer and adiabaticrapid passage in multilevel systems with multiphoton couplingbetween levels. Additionally, we examine strong field control of afour-level atomic interferometer and show how interference in atarget state changes from resonant pathways in the frequency domainto time-domain interference via a singe path.Further, we use shaped femtosecond pulses to demonstrate aphenomenon in which a three-level atom becomes a modulator of anultrafast pulse. The results are based on a pump-probe scheme thatis very similar to Electromagnetically Induced Transparency (EIT).Important dynamics associated with a time-dependent coupling fieldare examined. Lastly, we extend previous work on two-photon drivensuperfluorescence from a shaped ultrafast drive laser and show howstimulated emission near threshold can turn modest coherent controlyields into essentially perfect discrimination between systems wherea control factor of about 104 is achieved between atomic andmolecular species.

Thomas Feurer

Roberto Buffa, Stefano Cavalieri, Marco V. Tognetti

We present the coherent control of the temporal shape of laser pulses obtained by exploiting the propagation dynamics of electromagnetically induced transparency. Temporal compression, as a special case of pulse tailoring, is discussed. We envisage applications in nonlinear optics processes and control of pulse shapes in the vacuum ultraviolet spectral region.

Chitra Rangan

Warren S. Warren

Jongseok Lim, Han-gyeol Lee, Jaeuk Kim +2 more

We show theoretically and experimentally that two-photon coherent control in a $V$-shape three-level system projects a one-photon coherent transient in a simple two-level system. The second- and third-order spectral phase terms of a shaped laser pulse play the roles of time and quadratic spectral phase, respectively, in conventional coherent transients. In a three-pulse coherent control experiment of atomic rubidium, the phase and amplitude of controlled transition probability is retrieved from a two-dimensional Fourier-transform spectral peak. It is hoped that this control scheme may harness coherent control capability on multidimensional Fourier-transform spectroscopy.