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Ultrafast Phenomena and Nanophotonics

Improved efficiency of generating femtosecond photon echoes from quantum dots using chirped pulses and time-resolved measurement by frequency up-conversion technique

Yuta Kochi, Yutaro Kinoshita, Sunao Kurimura, Kouichi Akahane, Junko Ishi‐Hayase

Published Mar 8, 2024• 1 citation
Publisher

Abstract

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.

DOI
10.1117/12.3002122

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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.
We have developed a quantum memory using quantum dots with a photon echo method for the storage of ultraweak femtosecond pulses. This quantum memory has a large bandwidth of 7.2 THz, which can be achieved due to the large inhomogeneous broadening of quantum dots. We successfully demonstrated femtosecond timebin pulse transfer to photon-echo-based quantum memory using quantum dots. We also succeeded in measuring the retrieved time-bin pulses as a photon echo from the quantum memory using a pulse-pumped frequency upconversion single-photon detector (UCSPD) with a temporal resolution of 429 fs. It is found that the retrieved time-bin photon echo pulse maintains the sub-picosecond time duration and the relative phase.
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.
Recently, quantum information processing and communications using photons have been attracting attention. To increase the density of transmitted photonic qubits, it is necessary to develop broadband quantum memories and detectors that can handle ultrashort pulses. Although rare-earth-ion doped quantum memories [1] have been widely studied, due to their storage bandwidth of ~GHz, they are incapable of storing ultrashort pulses. In our group, we used the photon echo (PE) method with quantum dots (QDs) to realize ultra-short femtosecond pulse storage. However, we encountered many difficulties in realizing this method such as low PE efficiency from the QDs and the insufficient temporal resolution of the avalanche single-photon detectors. To solve these problems, we have applied a new quantum control method and utilized an up-conversion single-photon detector (UCSPD) [2]. In this presentation, we will introduce the techniques “1. Time-resolving measurement by UCSPD,” “2. PE quantum memory using QDs” and “3. enhancement of PE signals.”
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.