Time-resolved CARS measurements of vibrational decoherence of I₂ isolated in matrix Ar

Time-resolved coherent anti-Stokes Raman scattering is applied to prepare and interrogate vibrational coherences on the ground electronic surface of molecular iodine isolated in Ar matrices. The coherence decay time shows a linear dependence on vibrational quantum numbers, for v = 3–15. The temperature dependence of decoherence rates is negligible for v < 7, in the experimental range T = 18–32 K. For a v = 13, 14 superposition, the temperature dependence indicates dephasing by a 66 cm–¹ pseudo-local phonon, just outside the Debye edge of the solid. The accuracy of the data is limited due to two-photon induced dissociation of the molecule, which process is characterized using polarized fields. The T → 0 limit of dephasing is discussed

The manipulation of massive ro-vibronic superpositions using time-frequency-resolved coherent anti-Stokes Raman scattering (TFRCARS): from quantum control to quantum computing

Molecular ro-vibronic coherences, joint energy-time distributions of quantum amplitudes, are selectively prepared, manipulated, and imaged in Time-Frequency-Resolved Coherent Anti-Stokes Raman Scattering (TFRCARS) measurements using femtosecond laser pulses. The studies are implemented in iodine vapor, with its thermally occupied statistical ro-vibrational density serving as initial state. The evolution of the massive ro-vibronic superpositions, consisting of 1000 eigenstates, is followed through two-dimensional images. The first- and second-order coherences are captured using time-integrated frequency-resolved CARS, while the third-order coherence is captured using time-gated frequency-resolved CARS. The Fourier filtering provided by time integrated detection projects out single ro-vibronic transitions, while time-gated detection allows the projection of arbitrary ro-vibronic superpositions from the coherent third-order polarization. Beside the control and imaging of chemistry, the controlled manipulation of massive quantum coherences suggests the possibility of quantum computing. We argue that the universal logic gates necessary for arbitrary quantum computing - all single qubit operations and the two-qubit controlled-NOT (CNOT) gate - are available in time resolved four-wave mixing in a molecule. The molecular rotational manifold is naturally "wired" for carrying out all single qubit operations efficiently, and in parallel. We identify vibronic coherences as one example of a naturally available two-qubit CNOT gate, wherein the vibrational qubit controls the switching of the targeted electronic qubit.Comment: PDF format. 59 pages, including 22 figures. To appear in Chemical Physic

Atomic oxygen in solid deuterium

Atomic oxygen is photogenerated in solid D₂ by 193 nm irradiation of samples initially doped with molecular oxygen. The atoms are detected by laser induced fluorescence over the O(¹S→¹D) transition, which occurs at 559 nm, with a fluorescence lifetime of 230 ms. The absorption leading to this emission is indirect, attributed to O₂(X):O( ³P) pairs. Complementary studies are carried in solid D₂ co-doped with Xe and O₂, in which in addition to ionic XeO centers, the atomic O(¹S→¹D) transition with a radiative lifetime of 50 ms is observed. The photogeneration of the atomic centers, and stability of atomic and molecular emissions, are sensitive to sample preparation and thermal and irradiation histories. In annealed solids, at temperatures below 6.5 K, the atomic emission does not bleach, implying that the vertically prepared O(¹D) atoms undergo intersystem crossing to form O(³P) rather than react with D₂. The barrier to insertion on the O(¹D)+D₂ potential energy surface in solid D₂ is explained as a many-body polarization effect. The recombination of O(³P) atoms can be initiated thermally, and monitored by their thermoluminescence over the molecular O₂(A′ →X) transition. The thermal onset of recombination varies between 5.5 K and 9 K, depending on the sample preparation method. In all cases, the thermally induced recombination is catastrophic, accompanied by thermal runaway, pressure burst, and material loss. This is interpreted as indication that the process is initiated by self-diffusion of the host, consistent with the notion that atomic O centers stabilize the host lattice

Diagnostics of spectrally resolved transient absorption : surface plasmon resonance of metal nanoparticles

Time and frequency resolved transient absorption measurements yield two-dimensional images that map the dynamical correlation between the center and width of the scattering function. Global analysis of such data allows unique diagnostics of the mechanics underlying the time evolution. We specialize in the case of surface plasmon resonances of optically driven nanoparticles. We present a catalog of 2D maps that can be used to fingerprint physically meaningful cases, and we provide two experimental examples to illustrate the diagnostic value of the maps and their utility in extracting the various time constants at play. In silver nanorods, the experiment shows a π/2 phase shift between the oscillations of the center and the width of the plasmon resonance. Inspection of the maps allows the assignment that the center of the plasmon resonance tracks the strain in shape-oscillations, while the width tracks the strain rate. This finding is the basis of the novel mechanism of plasmon damping due to electron scattering from the electrophoretic potential generated by the motion of the interfacial double layer in colloidal nanoparticles. Measurements in gold nanoparticles show over-damped oscillations, which obscure the phase correlation between the center and width of the plasmon. The damping is dominated by inhomogeneous dephasing, and the time dependence of the width, which follows the temperature of the nanoparticles, and is diagnostic of the interband transition contribution to the plasmon resonance