Spectral Tailoring of Inhomogeneous Optical Response Using Two-Dimensional Coherent Spectroscopy

TL;DR

This work addresses tailoring the coherent nonlinear optical response of inhomogeneous ensembles using two-dimensional coherent spectroscopy (2DCS). It compares two spectral tailoring strategies: a bandwidth-constrained prepulse method that induces Rabi oscillations and a bandwidth-agnostic double-pulse (DP) method that relies on interference between temporally separated pulses. The authors derive and analyze the nonlinear signal behavior under both schemes, showing that prepulse efficacy depends on matching the prepulse bandwidth to the ensemble $FWHM$, while the DP approach enables predetermined periodic spectral modulation and selective switching through the relative delay and phase, without bandwidth limits. The findings suggest robust routes to optical switching and quantum memory applications in inhomogeneous ensembles, enabled by phase-controlled interference in the DP scheme.

Abstract

Controlling the coherent optical response of inhomogeneous ensembles is a key challenge in advancing light-matter interaction engineering. We present a comparative study of two spectral tailoring approaches using two-dimensional coherent spectroscopy (2DCS): the prepulse and double-pulse (DP) methods. In the prepulse scheme, a high-intensity pulse induces Rabi oscillations, modulating the 2D spectral amplitude and lineshape when its spectral bandwidth matches the ensemble full width at half maximum (FWHM). To overcome this limitation, the DP method employs variable inter-pulse delay to generate predetermined periodic spectral modulation without bandwidth constraints. Moreover, tuning the relative phase between DP pulses allows selective switching of frequency components, enabling controlled enhancement or suppression of distinct spectral features. These observations highlight that, while the prepulse approach is constrained by spectral bandwidth, the DP method provides a more versatile and reliable route to manipulate the coherent optical response of inhomogeneous ensembles. We are hoping these findings might stimulate further research in optical switching and coherent storage for quantum memory devices using inhomogeneous ensembles.

Figures (8)

• Figure 1: (a) Optical prepulse excitation sequence is shown here for 2DCS simulation. Delays among the prepule, A*, B, C and the signal are demonstrated as $\Delta$t, $\tau$, $T$, and $t$, respectively. (b) Energy-level scheme for two-level inhomogeneous ensemble is shown with $\ket{0}$ and $\ket{1}$ representing ground and excited states respectively. (c)-(e) Possible quantum pathways for two-level system with prepulse excitation are shown using double-sided Feynman diagram.
• Figure 2: (a) $\rho_{11}(\omega,\Theta)$ excited population as a function of detuning energy and pulse-area $\Theta$ is demonstrated. (b) $2-3\rho_{11}(\omega,\Theta)$ variation as a function of detuning energy and pulse-area $\Theta$ is demonstrated.
• Figure 3: (a) $2-3\rho_{11}(\omega_{i},\Theta)$ *$g(\omega_{i})$ population weighted by inhomogeneous probability distribution function is demonstrated with changing pulse-area $\Theta$. (b) Magnitude of modulated population variation as a function of pulse-area $\Theta$ is demonstrated.
• Figure 4: (a) Absolute part of the 2D spectrum and (b) corresponding diagonal spectral line shape for without pre-pulse, $\Theta = 0 \pi$. (c) Modulated 2D spectral amplitude showing Rabi oscillations at a prepulse pulse area of $\Theta = 0.85\pi$, and (d) the corresponding modulated diagonal spectral line shape. (e) and (f) Rabi-oscillation-induced modulation in the 2D spectral amplitude and the corresponding diagonal spectral line shape observed at a higher prepulse intensity with a pulse area of $\Theta = 1\pi$.
• Figure 5: Prepulse spectral-bandwidth-dependent modulation, manifested as Rabi oscillations, is shown in the diagonal lineshape at a fixed prepulse pulse-area of $\Theta = \pi$. Dashed line represents normalized diagonal spectral lineshapes for varying prepulse spectra and solid line shows the inhomogeneous Gaussian distribution with a full-width half-maximum (FWHM) of 3 meV.