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Nanophotonics

Enhancement of Femtosecond Photon Echo Signals From an Inhomogeneously Broadened InAs Quantum Dot Ensemble Using Chirped Pulses

Yuta Kochi, Yutaro Kinoshita, Masanari Watanabe, Ryutaro Ide, Kouichi AKAHANE, Junko Ishi‐Hayase

Published Feb 1, 2026• 0 citations

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 demonstrate that chirped rephasing pulses satisfying adiabatic conditions enable robust adiabatic rapid passage (ARP) across an inhomogeneously broadened InAs QD ensemble. This approach achieves uniform population inversion and broadband rephasing, overcoming the limitations of transform-limited excitation. Experimentally, we observe a 3.2-fold enhancement of the PE signal in dense, self-assembled InAs QDs operating at telecom wavelengths. Numerical simulations based on a two-level model reproduce the experimentally observed ARP-induced enhancement, validating the underlying physical mechanism. These results establish ARP as an effective and scalable method for coherent control in THz-broadened QD ensembles, opening a pathway toward ultrafast and broadband optical quantum memory and communication in the telecom band.

DOI: 10.1002/nap2.70013

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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 demonstrate that chirped rephasing pulses satisfying adiabatic conditions enable robust adiabatic rapid passage (ARP) across an inhomogeneously broadened InAs QD ensemble. This approach achieves uniform population inversion and broadband rephasing, overcoming the limitations of transform-limited excitation. Experimentally, we observe a 3.2-fold enhancement of the PE signal in dense, self-assembled InAs QDs operating at telecom wavelengths. Numerical simulations based on a two-level model reproduce the experimentally observed ARP-induced enhancement, validating the underlying physical mechanism. These results establish ARP as an effective and scalable method for coherent control in THz-broadened QD ensembles, opening a pathway toward ultrafast and broadband optical quantum memory and communication in the telecom band.

In quantum information technology, it is necessary to develop a light-matter quantum interface that transfers and stores quantum information. As a bandwidth of quantum entangled photon pairs used for quantum information increases, a quantum interface with broad bandwidth will be required. The combination of quantum dot (QD) ensemble and photon echo (PE) method is one of promising methods for broadband quantum interface. Since the bandwidth of the quantum interface using this method is limited only by the inhomogeneous width of the QDs, it is possible to implement a quantum interface with the bandwidth of 10 THz at telecommunication wavelength. However, in the PE method, the spatial inhomogeneousity of the laser intensity and the inhomogeneousity of the resonance frequency of the QDs result in the uniform quantum control of excitons in QDs. As a result, the regeneration eﬃciency of the PE light is significantly deteriorated. To solve this problem, it is effective to introduce a quantum control method using chirped pulses (Adaptive Rapid Passages; ARPs) which is robust to inhomogeneousities. In this study, we demonstrate that the regeneration efficiency of PE in inhomogeneous QDs can be improved by ARPs using femtosecond pulses. By performing numerical simulation and optical experiments, it was found that the regeneration efficiency improves as the chirp amount and the pulse area increase, and saturates at a certain condition.

We developed a THz bandwidth quantum memory using a photon echo technique in InAs quantum dot ensemble with a large inhomogeneous broadning. To improve photon echo generation efficiency, we applied Adiabatic Rapid Passage (ARP) technique to quantum manipulation of quantum memory. In addition, we developed pulse pumped up conversion single photon detector (UCSPD) which enables us to achieve the femtosecond scale temporal resolution and we successfully demonstrated femtosecond time bin photon echo signals.

An exciton in a quantum dot (QD) strongly couples to light, allowing the ultrafast manipulation of the quantum states on the order of femtoseconds [1]. Since a QD exciton can be regarded as a two-level system, the excitonic state can be manipulated coherently via Rabi oscillations depending on the electric field of the excitation pulse and the resonant frequency of the QD exciton. However, uniformly manipulating the exciton ensemble in a large number of QDs using ultrashort pulses is quite difficult due to the inhomogeneous distributions of the excitonic resonant frequency and the laser intensity for each QD. Adiabatic rapid passage (ARP) has been demonstrated to overcome this problem because it provides a quantum manipulation technique robust over the inhomogeneities [2], [3] by using chirped pulses (CP) instead of using Fourier transform-limited pulses (TLP). While ARP has been studied extensively in two-level systems with inhomogeneous linewidths up to GHz, it has not been rarely applied to two-level systems with THz inhomogeneous linewidths such as QDs. In this work, we experimentally demonstrate the ultrafast coherent transfer of the exciton population via ARP in two kinds of QD samples; 150-layer stacked InAs QDs and 50-layer stacked InAs QDs embedded in a resonator (Fig. 1(a)).

We investigate the dephasing mechanism of optically-induced exciton coherence in an ensemble of InAs self-assembled quantum dots (QDs) using a two-pulse photon-echo (PE) technique. The sample was fabricated on an InP (311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150-layer stacked QD structure for enhancing the PE signal intensity. We show the measured decay time of PE signal intensity for resonant excitation of ground-state transition is extremely long, which corresponds to ultralong coherence times of excitons in our QDs. We confirmed that non-radiative population relaxation and pure dephasing are considerably smaller than the radiative relaxation at low temperature. Furthermore, we demonstrate the ultrafast coherent control of QD exciton polarization by changing the pulse areas (Rabi oscillations) in the PE experiment. We also propose a new scheme for implementing QD quantum memory by using the PE technique.

Photon-echo-based quantum memories use inhomogeneously broadened, optically thick ensembles of absorbers to store a weak optical signal and employ various protocols to rephase the atomic coherences for information retrieval. We study the application of two consecutive, frequency-chirped control pulses for coherence rephasing in an ensemble with a ``natural'' inhomogeneous broadening. Although propagation effects distort the two control pulses differently, chirped pulses that drive adiabatic passage can rephase atomic coherences in an optically thick storage medium. Combined with spatial phase-mismatching techniques to prevent primary echo emission, coherences can be rephased around the ground state to achieve secondary echo emission with close to unit efficiency. Potential advantages over similar schemes working with $\ensuremath{\pi}$ pulses include greater potential signal fidelity, reduced noise due to spontaneous emission, and better capability for the storage of multiple memory channels.