Current experimental and theoretical progress toward the goal of controlling quantum dynamics is summarized. Two key developments have now revitalized the field. First, appropriate ultrafast laser pulse shaping capabilities have only recently become practical. Second, the introduction of engineering control concepts has put the required theoretical framework on a rigorous foundation. Extrapolations to determine what is realistically possible are presented.

https://science.sciencemag.org/content/sci/259/5101/1581.full.pdf

Coherent control of quantum dynamics: the dream is alive.

Coherent quantum control1,2,3 has attracted interest as a means to influence the outcome of a quantum-mechanical interaction. In principle, the quantum system can be steered towards a desired state by its interaction with light. For example, in photoinduced transitions between atomic energy levels, quantum interference effects can lead to enhancement or cancellation of the total transition probability. The interference depends on the spectral phase distribution of the incident beam; as this phase distribution can be tuned, the outcome of the interaction can in principle be controlled. Here we demonstrate that a femtosecond laser pulse can be tailored, using ultrashort pulse-shaping4,5,6,7 techniques, to control two-photon transitions in caesium. By varying the spectral phases of the pulse components, we observe the predicted cancellation of the transitions due to destructive quantum interference; the power spectrum and energy of these ‘dark pulses’ are unchanged. We also show that the pulse shape can be modified extensively without affecting the two-photon transition probability.

Coherent quantum control of two-photon transitions by a femtosecond laser pulse

Articles you may be interested in Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation Rev. Impulsive effects of phaselocked pulse pairs on nuclear motion in the electronic ground state Fluorescencedetected wave packet interferometry: Time resolved molecular spectroscopy with sequences of femtosecond phaselocked pulses

/pdf/time-resolved-dynamics-of-isolated-molecular-systems-studied-zdn33nvohv.pdf

Time resolved dynamics of isolated molecular systems studied with phase‐locked femtosecond pulse pairs

We consider the control of molecular dynamics using tailored light fields, based on a phase space theory of control [Y. J. Yan et al., J. Phys. Chem. 97, 2320 (1993)]. This theory enables us to calculate, in the weak field (one‐photon) limit, the globally optimal light field that produces the best overlap for a given phase space target. We present as an illustrative example the use of quantum control to overcome the natural tendency of quantum wave packets to delocalize on excited state potential energy curves. Three cases are studied: (i) a ‘‘molecular cannon’’ in which we focus an outgoing continuum wave packet of I2 in both position and momentum, (ii) a ‘‘reflectron’’ in which we focus an incoming bound wave packet of I2, and (iii) the focusing of a bound wave packet of Na2 at a turning point on the excited state potential using multiple light pulses to create a localized wave packet with zero momentum. For each case, we compute the globally optimal light field and also how well the wave packet produced by this light field achieves the desired target. These globally optimal fields are quite simple and robust. While our theory provides the globally optimal light field in the linear, weak field regime, experiment can in reality only provide a restricted universe of possible light fields. We therefore also consider the control of molecular quantum dynamics using light fields restricted to a parametrized functional form which spans a set of fields that can be experimentally realized. We fit the globally optimal electric field with a functional form consisting of a superposition of subpulses with variable parameters of amplitude, center time, center frequency, temporal width, relative phase, and linear and quadratic chirp. The best fit light fields produce excellent quantum control and are within the range of experimental possibility. We discuss relevant experiments such as ultrafast spectroscopy and ultrafast electron and x‐ray diffraction which can in principle detect these focused wave packets.

/pdf/optical-control-of-molecular-dynamics-molecular-cannons-3qytu8fpzb.pdf

Optical control of molecular dynamics: Molecular cannons, reflectrons, and wave‐packet focusers

We recently introduced frequency-resolved optical gating (FROG), a technique for measuring the intensity and phase of an individual, arbitrary, ultrashort laser pulse. FROG can use almost any instantaneous optical nonlinearity, with the most common geometries being polarization gate, self-diffraction, and second-harmonic generation. The experimentally generated FROG trace is intuitive, visually appealing, and can yield quantitative information about the pulse parameters (such as temporal and spectral width and chirp). However, the qualitative and the quantitative features of the FROG trace depend strongly on the geometry used. We compare the FROG traces for several common ultrashort pulses for these three common geometries and, where possible, develop scaling rules that allow one to obtain quantitative information about the pulse directly from the experimental FROG trace. We illuminate the important features of the various FROG traces for transform-limited, linearly chirped, self-phase modulated, and nonlinearly chirped pulses, pulses with simultaneous linear chirp and self-phase modulation, and pulses with simultaneous linear chirp and cubic phase distortion, as well as double pulses, pulses with phase jumps, and pulses with complex intensity and phase substructure.

Comparison of ultrashort-pulse frequency-resolved-optical-gating traces for three common beam geometries

A technique for producing phase-related picosecond optical pulses is described. A sequence of two phase-related pulses, well separated in time, is applied to the D1 line in Na vapor. When the phase between the two pulses is scanned, oscillations in the incoherent fluorescence are observed. This demonstrates the well-defined phase relationship between the pulses. Measuring the amplitude of the oscillations as a function of pulse separation yields the Na optical coherence decay. A beat arising from the ground-state hyperfine splitting is observed, and the results agree well with calculation.

https://web.stanford.edu/group/fayer/articles/117.pdf

Picosecond time-scale phase-related optical pulses: measurement of sodium optical coherence decay by observation of incoherent fluorescence

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Picosecond time-scale phase-related optical pulses: measurement of sodium optical coherence decay by observation of incoherent fluorescence