Structured beam controlled super-resolution in quantum dots via rapid adiabatic passage

TL;DR

This work tackles diffraction-limited imaging by employing rapid adiabatic passage (RAP) in a two-level quantum dot driven by two structured beams with opposite chirps. A variational master equation incorporating exciton-phonon coupling is developed to model temperature-dependent decoherence and to interpolate between weak-coupling and polaron regimes, enabling accurate prediction of super-resolution spot formation. The authors show that Bessel-modulated truncated SG and LG beams can suppress unwanted side rings, and that higher pulse areas mitigate phonon-induced distortion, yielding sub-diffraction spots as small as tens of nanometers (e.g., ~26 nm at 4 K). The approach suggests practical routes for nanoscale imaging and bioimaging with quantum dots using controllable optical fields and phonon-aware dynamics.

Abstract

We theoretically investigate rapid adiabatic passage (RAP) based super-resolution microscopy in a two-level quantum dot (QD) system. The system consists of a QD interacting with two structured beams, accompanied by chirping and a time delay. The central concept of this work is inspired by the stimulated emission depletion (STED) microscopy technique. To understand the physical mechanism behind super-resolved spot formation, we employ a variational master equation for the density matrix, incorporating both radiative and non-radiative decay processes. A suitably chosen spatiotemporal envelope of the structured beams enables the formation of a super-resolved image. Unwanted low-intensity circular rings around the focal spot are suppressed using Bessel-modulated truncated structured Laguerre-Gaussian (LG) and super-Gaussian (SG) beams. We also study the temperature dependence of the imaging scheme. The numerical results confirm that at low pulse areas, exciton-phonon coupling distorts the image, whereas at higher pulse areas, exciton-phonon decoupling preserves the image resolution. Hence, the proposed scheme may open up new possibilities for nanoscale imaging and bioimaging applications using QDs.

Figures (10)

• Figure 1: Schematic diagram of two-level quantum dot interacting with phonon bath. Two spatiotemporal beams interact with the system of Rabi frequencies $\Omega_{G}$ and $\Omega_{D}$. The spontaneous emission decay rate from $|1\rangle$ to $|2\rangle$ is given by $\gamma$. The two beams interact resonantly with both the levels.
• Figure 2: Excited state population as a function of pulse area and chirping. The color bar denotes the population of the excited state.
• Figure 3: Population transfer via RAP. The first pulse with positive chirp of 3.24 ps$^{-2}$ and pulse area greater than $\pi$ transfers the population to the excited state and the subsequent pulse with chirp -3.24 ps$^{-2}$ and pulse area greater than $\pi$ bring down the excited state population to ground state. Both the pulse has a width 1.3$\tau_n$. The electron-phonon coupling strength $\alpha_p$ = 0.027 ps$^2$.
• Figure 4: The 3-D intensity distribution of (a) SG beam of width 1.7$l$ and (b) LG spatiotemporal beam of width $l$
• Figure 5: Population of the excited state vs. spatial extent in QD system. The applied spatiotemporal beams SG has waist $w_G$ = 1.7$l$, and LG has waist $w_D$ = $l$. The spatial distribution of the excited state population is shown at $\gamma_n$t = 30. Other parameters are the same as in Fig. \ref{['fig:3']}.