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Register a new userQuantum model for Impulsive Stimulated Raman Scattering
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The interaction between ultrashort light pulses and non-absorbing materials is dominated by Impulsive Stimulated Raman Scattering (ISRS). The description of ISRS in the context of pump&probe experiments is based on effective classical models describing the interaction between the phonon and pulsed electromagnetic fields. Here we report a theoretical description of ISRS where we do not make any semi-classical approximation and we treat both photonic and phononic degrees of freedom at the quantum level. The results of the quantum model are compared with semiclassical results and validated by means of spectrally resolved pump&probe measurements on $alpha$-quartz.
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In Impulsive Stimulated Raman Scattering vibrational oscillations, coherently stimulated by a femtosecond Raman pulse, are real time monitored and read out as intensity modulations in the transmission of a temporally delayed probe pulse. Critically, in order to retrieve broadband Raman spectra, a fine sampling of the time delays between the Raman and probe pulses is required, making conventional ISRS ineffective for probing irreversible phenomena and/or weak scatterers typically demanding long acquisition times, with signal to noise ratios that crucially depend on the pulse fluences and overlap stabilities. To overcome such limitations, here we introduce Chirped based Impulsive Stimulated Raman Scattering (CISRS) technique. Specifically, we show how introducing a chirp in the probe pulse can be exploited for recording the Raman information without scanning the Raman-probe pulse delay. Then we experimentally demonstrate with a few examples how to use the introduced scheme to measure Raman spectra.
The global optimum for valence population transfer in the NO$_2$ molecule driven by impulsive x-ray stimulated Raman scattering of one-femtosecond x-ray pulses tuned below the Oxygen K-edge is determined with the Multiconfiguration Time-Dependent Hartree-Fock method, a fully-correlated first-principles treatment that allows for the ionization of every electron in the molecule. Final valence state populations computed in the fixed-nuclei, nonrelativistic approximation are reported as a function of central wavelength and intensity. The convergence of the calculations with respect to their adjustable parameters is fully tested. Fixing the 1fs duration but varying the central frequency and intensity of the pulse, without chirp, orientation-averaged maximum population transfer of 0.7% to the valence B$_1$ state is obtained at an intensity of 3.16$times$10$^{17}$ W cm$^{-2}$, with the central frequency substantially 6eV red-detuned from the 2nd order optimum; 2.39% is obtained at one specific orientation. The behavior near the global optimum, below the Oxygen K-edge, is consistent with the mechanism of nonresonant Raman transitions driven by the near-edge fine structure oscillator strength.
We have calculated the resonant and nonresonant contributions to attosecond impulsive stimulated electronic Raman scattering (SERS) in regions of autoionizing transitions. Comparison with Multiconfiguration Time-Dependent Hartree-Fock (MCTDHF) calculations find that attosecond SERS is dominated by continuum transitions and not autoionizing resonances. These results agree quantitatively with a rate equation that includes second-order Raman and first-and second-order photoionization rates. Such rate models can be extended to larger molecular systems. Our results indicate that attosecond SERS transition probabilities may be understood in terms of two-photon generalized cross sections even in the high-intensity limit for extreme ultraviolet wavelengths.
We consider the coherent stimulated Raman process developing in an optically dense disordered atomic medium, which can also incoherently scatter the light over all outward directions. The Raman process is discussed in the context of a quantum memory scheme and we point out the difference in its physical nature from a similar but not identical protocol based on the effect of electromagnetically induced transparency (EIT). We show that the Raman and EIT memory schemes do not compete but complement one another and each of them has certain advantages in the area of its applicability. We include in our consideration an analysis of the transient processes associated with switching the control pulse off or on and follow how they modify the probe pulse dynamics on the retrieval stage of the memory protocol.
Stimulated Raman adiabatic passage (STIRAP) is a widely-used technique of coherent state-to-state manipulation for many applications in physics, chemistry, and beyond. The adiabatic evolution of the state involved in STIRAP, called adiabatic passage, guarantees its robustness against control errors, but also leads to problems of low efficiency and decoherence. Here we propose and experimentally demonstrate an alternative approach, termed stimulated Raman user-defined passage (STIRUP), where a parameterized state is employed for constructing desired evolutions to replace the adiabatic passage in STIRAP. The user-defined passages can be flexibly designed for optimizing different objectives for different tasks, e.g. minimizing leakage error. To experimentally benchmark its performance, we apply STIRUP to the task of coherent state transfer in a superconducting Xmon qutrit. We found that STIRUP completed the transfer more then four times faster than STIRAP with enhanced robustness, and achieved a fidelity of 99.5%, which is the highest among all recent experiments based on STIRAP and its variants. In practice, STIRUP differs from STIRAP only in the design of driving pulses; therefore, most existing applications of STIRAP can be readily implemented with STIRUP.
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