Enhancement of femtosecond photon echo signals from an inhomogeneously broadened InAs quantum dot ensemble using chirped pulses

TL;DR

This work tackles the bottleneck of implementing photon-echo quantum memories in broadband, inhomogeneously broadened solid-state media by using adiabatic rapid passage with chirped pulses to coherently control a dense InAs QD ensemble at telecom wavelengths. The authors develop a two-level ARP model with Lindblad dynamics and integrate over THz-scale detuning and spatial inhomogeneity to predict robust rephasing, supported by an experiment in InAs QD ensembles at telecom wavelengths. They demonstrate a 3.2-fold enhancement of photon echo intensity compared to transform-limited rephasing, while maintaining sub-picosecond echo widths and extending coherence time under ARP; results align with simulations, validating the ARP picture. These findings establish ARP as a scalable approach for broadband coherent control in InAs QD ensembles, with potential applications in ultrafast, broadband optical memory and telecom-compatible quantum photonics.

Abstract

Photon echo (PE) techniques offer a promising approach to optical quantum memory, yet their implementation in conventional platforms, such as rare-earth-ion-doped crystals, is hindered by limited bandwidths. Semiconductor quantum dot (QD) ensembles, featuring THz-scale inhomogeneous broadening and sub-picosecond dynamics, provide an attractive alternative for ultrafast applications. However, achieving coherent control across such broad spectral ranges remains challenging due to detuning and spatial field inhomogeneities, which reduce PE efficiency. In this work, we experimentally demonstrated adiabatic rapid passage (ARP)-enhanced PE in dense, self-assembled InAs QD ensembles exhibiting THz-scale inhomogeneous broadening and operating at telecom wavelengths, achieving a 3.2-fold increase in echo efficiency. Chirped control pulses designed to satisfy adiabatic conditions across the ensemble enable broadband rephasing. Numerical simulations based on a two-level model reproduce the key experimental observations, including the ARP-induced enhancement, thereby validating the underlying physical picture. These results establish ARP as a robust and scalable approach for coherent control in InAs QD ensembles, with potential applications for ultrafast and broadband optical communication in the THz spectral region.

Figures (5)

• Figure 1: (a) PE pulse sequence of our setup. We applied double rephasing pulses (rephasing 1 and 2). Blue line represents the change in frequency of the rephasing pulses. (b) Comparison of final Bloch vector states in population inversion for single TFL and 1.2 ps chirped pulse (ARP) excitation. The magenta arrows represent the final positions of the torque vectors, while the solid lines trace the trajectories of the Bloch vectors. (c) Comparison of final Bloch vector states in PE for TFL and ARP rephasings, starting from the superposition state (v in this figure) as the initial condition.
• Figure 2: (a) Structure of the InAs QD ensemble integrated with a resonator. (b) Photoluminescence spectrum of the QD ensemble at 4.7 K. The red line indicates the spectrum of the OPO laser. (c) Optical setup used for PE experiment. (PBS: polarizing beam splitter, BS: half beam splitter, $\lambda/2$: half wave plate, $\lambda/4$: quarter wave plate.) (d) GVD curve of the glass rod based on literature values at room temperature. (e) Experimental result of GDD with different glass rod length. The red solid line represents a fit to the experimental data.
• Figure 3: Simulation results for pulse area dependence of PE intensity: (a) with a flat-top and (b) with a Gaussian electric field profile. The red area indicates the pulse area in the PE waveform measurement experiment. PE waveforms corresponding to the red area $\sqrt{I}=0.65$ in (b) are shown in (c).
• Figure 4: Storage time $t_{\rm PE}$ dependence of PE intensity (a) without and (b) with ARP. Red squares denote peak PE intensity, red solid lines are exponential fits, and black solid lines are PE waveforms. Insets show expanded PE traces at 120 and 520 ps.
• Figure 5: (a) Experimental results of PE pulse area dependence with different chirp amounts. (b) PE waveforms corresponding to the red areas in (a). Experimental waveforms were obtained using heterodyne detection, resulting in cross-correlated waveforms. The pulse width values shown are estimates of the original pulse width, derived from deconvolution of the waveforms after fitting with a Gaussian function.