5 research outputs found
Chirped Pulse Control of Raman Coherence in Atoms and Molecules
A novel chirped pulse control scheme is presented based on Coherent
Anti-Stokes Raman Spectroscopy (C-CARS) aiming at maximizing the vibrational
coherence in atoms and molecules. The scheme utilizes chirping of the three
incoming pulses, the pump, the Stokes and the probe, in the four-wave mixing
process of C-CARS to fulfill the adiabatic passage conditions. The derivation
of the scheme is based on simplifying the four-level system into a
'super-effective' two level system via rotating wave approximation and
adiabatic elimination of the excited state manifold. The robustness, spectral
selectivity and adiabatic nature of C-CARS method may prove useful for sensing,
imaging, and detection. It is demonstrated that the selectivity in excitation
of vibrational degrees of freedom can be controlled by carefully choosing the
spectral chirp rate of the pulses. The C-CARS control scheme is applied to a
surrogate methanol molecule to generate an optimal anti-Stokes signal
backscattered from a cloud of molecules a kilometer away. The theory is based
on the solution of the coupled Maxwell-Liouville von Neumann equations and
focuses on the quantum effects induced in the target molecules by the control
pulse trains. The propagation effects of pulses through the medium are
evaluated and the buildup of the molecular-specific anti-Stokes signal is
demonstrated numerically. A deep learning technique, using Convolutional Neural
Networks (CNN), is implemented to characterize the control pulses and evaluate
time-dependent phase characteristics from them. The effects of decoherence
induced by spontaneous decay and collisional dephasing are also examined.
Additionally, we present the technique of Fractional Stimulated Raman Adiabatic
Passage (F-STIRAP) and demonstrate that it can be utilized for remote detection
in a multi-level system by creation of a maximally coherent superposition
state
Chirped Fractional Stimulated Raman Adiabatic Passage
Stimulated Raman Adiabatic Passage (STIRAP) is a widely used method for
adiabatic population transfer in a multilevel system. In this work, we study
STIRAP under novel conditions and focus on the fractional, F-STIRAP, which is
known to create a superposition state with the maximum coherence. In both
configurations, STIRAP and F-STIRAP, we implement pulse chirping aiming at a
higher contrast, a broader range of parameters for adiabaticity, and enhanced
spectral selectivity. Such goals target improvement of quantum imaging, sensing
and metrology, and broaden the range of applications of quantum control
techniques and protocols. In conventional STIRAP and F-STIRAP, two-photon
resonance is required conceptually to satisfy the adiabaticity condition for
dynamics within the dark state. Here, we account for a non-zero two-photon
detuning and present control schemes to achieve the adiabatic conditions in
STIRAP and F-STIRAP through a skillful compensation of the two-photon detuning
by pulse chirping. We show that the chirped configuration - C-STIRAP - permits
adiabatic passage to a predetermined state among two nearly degenerate final
states, when conventional STIRAP fails to resolve them. We demonstrate such a
selectivity within a broad range of parameters of the two-photon detuning and
the chirp rate. In the C-F-STIRAP, chirping of the pump and the Stokes pulses
with different time delays permits a complete compensation of the two-photon
detuning and results in a selective maximum coherence of the initial and the
target state with higher spectral resolution than in the conventional F-STIRAP
Mirrorless lasing: a theoretical perspective
Mirrorless lasing has been a topic of particular interest for about a decade
due to promising new horizons for quantum science and applications. In this
work, we review first-principles theory that describes this phenomenon, and
discuss degenerate mirrorless lasing in a vapor of Rb atoms, the mechanisms of
amplification of light generated in the medium with population inversion
between magnetic sublevels within the line, and challenges associated
with experimental realization