Quantum memories play a pivotal role in establishing long-distance communication by entanglement swapping operations within quantum repeater nodes. Constructing such a quantum memory involves Electromagnetically Induced Transparency (EIT) within atomic vapors at room temperatures to store highly attenuated coherent light pulses down to the level of single photons. The photons may be generated from quantum nodes containing stationary quantum systems, such as atoms or semiconductor quantum dots (QDs). QDs serve as a potent source of quantum light, furnishing bright, precisely timed single photons of exceptional purity. While previous endeavors have demonstrated the integration of QDs with atomic vapors through techniques like “slow light,” the development of a dedicated quantum memory for QDs remains unmatched. In our study, we introduce an EIT quantum memory hosted within warm cesium vapor. Our approach exhibits a good efficiency in storing faint coherent light pulses at the single photon level. Moreover, the measured bandwidth of around 200 MHz approaches the Fourier-limited emission characteristics of QDs. We present initial efforts to match the emission from QDs with our quantum memory and discuss application scenarios of room temperature EIT quantum memories.
Solid-state single and entangled photon emitters linked coherently over long distances with optical fibers enable a new generation of quantum-based communications networks. Currently, epitaxial semiconductor quantum dots (QDs) pave the way as a scalable approach for fabricating deterministic non-classical light sources that can be integrated with other photonic or electronic components in miniaturized form. Here, we present a new quantum material system based on GaSb QDs formed by filling droplet-etched nanoholes [1,2], a technique which has been previously used for the state-of-the-art single- and entangled-photon sources in the GaAs-based materials emitting at wavelengths shorter than 800 nm [3-6]. We show that while the GaSb QDs exhibit high homogeneity and small fine structure splitting similarly to their GaAs counterparts, they also enable single-photon emission in the 3rd telecom window [7] with prospects for extending towards 2µm. These properties make them ideal candidates for quantum photonic applications requiring compatibility with Si-photonics and fiber-based telecom.
[1] J. Hilska et al. Cryst. Growth Des. 21 1917−1923, 2021
[2] A. Chellu et al. APL Materials 9, pp
Photonic wire bonds have been developed as an interface for the collection of single photon emission from quantum dots within a Bragg waveguide. When resonantly excited from the top of the waveguide via free space excitation a low multiphoton contribution in the quantum dot emission with g(2)(0) = (9.5 ± 1.4) × 10−2 is shown. Our measurements demonstrate the ability to collect single-photon emission from a ridge waveguide into an optical fiber via photonic wire bonds at cryogenic temperatures. This allows for a seamless plug-and-play operation of the fiber-coupled single-photon source. Furthermore, the demonstrated approach allows for resonance fluorescence excitation without the need for any additional cross-polarization filtering.
The development of quantum photonic technologies will fuel a paradigm shift in data processing and communication protocols. A controlled generation of non-classical states of light is a challenging task at the heart of such technologies. Epitaxially grown self- assembled semiconductor quantum dots (QDs) offer the advantages of deterministic generation of single photons and prospects of device integration. By growing such QD structures only in designated locations on (001) Si substrate, the quantum properties of the emitted photons could be tuned with the built-in thermal stress for generating highly entangled photon pairs.
Semiconductor quantum dots embedded into nanophotonic resonators are one of the best performing sources for single and entangled photons. For certain protocols a defined charge in the quantum dot is required and to increase the device yield, charge control is a desired feature of the nanophotonic structure. In this paper, we present our latest efforts towards such a highly efficient, charge tunable device. Numerical simulations optimizing a bridged circular Bragg grating are discussed and photoluminescence measurements of a charge tunable quantum dot are shown.
Quantum memories can substantially increase the efficiency of long-distance communications by synchronizing entanglement swapping operations in quantum repeater nodes. To build a quantum memory, electromagnetically induced transparency (EIT) in atomic vapors can be exploited to coherently store light pulses even at room temperatures. As a quantum source of light, semiconductor quantum dots (QD) offer bright on-demand single photons with high purity.4 Interfacing QDs with atomic vapors has been shown by “slow light” but a quantum memory for QDs is yet to be demonstrated. In this work, we develop an EIT quantum memory hosted in warm cesium vapor. Storage of faint coherent light pulses on the single photon level shows high storage efficiency. A measured bandwidth in the order of 200 MHz makes the memory compatible with the Fourier-limited emission of QDs embedded in micropillar cavities. We show the first attempts to interface the emission from a QD-micropillar with our quantum memory by finetuning the emission wavelength of the emitters to one of the hyperfine transitions in Cs, where the EIT memory takes place. This work sets the base for a hybrid quantum memory based on atomic ensembles for an on-demand semiconductor single-photon source.
Tunable entangled photon emitters based on cavity-enhanced GaAs quantum dots on micromachined piezoelectric substrates was recorded at SPIE Optics + Photonics held in San Diego, California, United States 2022.
Semiconductor quantum dots are excellent emitters of single photons. Often, the same mode is used to resonantly excite a QD and to collect the emitted single-photons, requiring cross polarization to separate out scattered laser light. This reduces the source brightness to ≤50%, and potentially eliminates their use in some quantum applications. We demonstrate a resonant-excitation approach to creating single photons that is free of any filtering whatsoever. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected cavity-waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode.
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