Abstract
Spectrally-tunable quantum light sources are key elements for the realization of long-distance quantum communication. A deterministically fabricated single-photon source with a photon extraction efficiency of η =(20 ± 2) %, a maximum tuning range of ΔE = 2.5 meV and a minimum g(2)(τ = 0) = 0.03 ± 0.02 is presented. The device consists of a single pre-selected quantum dot (QD) monolithically integrated into a microlens that is bonded onto a piezoelectric actuator via gold thermocompression bonding. Here, a thin gold layer simultaneously provides strain transfer and acts as a backside mirror for the QD-microlens to maximize the photon extraction efficiency. The QD-microlens structure is patterned via 3D in-situ electron-beam lithography (EBL), which allows us to pre-select and integrate suitable QDs based on their emission intensity and energy with a spectral accuracy of 1 meV for the final device. Together with strain fine-tuning, this enables the scalable realization of single-photon sources with identical emission energy. Moreover, we show that the emission energy of the source can be stabilized to µeV accuracy by closed-loop optical feedback. Thus, the combination of deterministic fabrication, spectral-tunability and high broadband photon-extraction efficiency makes the QD-microlens single-photon source an interesting building block for the realization of quantum communication networks.
Highlights
Quantum communication protocols promise secure data transmission based on single-photon technology [1,2,3]
The quantum dot (QD)-microlens structure is patterned via 3D in-situ electron-beam lithography (EBL), which allows us to pre-select and integrate suitable QDs based on their emission intensity and energy with a spectral accuracy of 1 meV for the final device
We present a bright spectrally-tunable single-photon source based on a deterministically fabricated QD microlens combined with a piezoelectric actuator by a flip-chip goldbonding technique
Summary
Quantum communication protocols promise secure data transmission based on single-photon technology [1,2,3]. Two recent experiments, which demonstrate entanglement swapping of entangled photon pairs consecutively emitted by the same emitter, impressively underline the high potential of semiconductor QDs in this regard [5,6] Beyond such proof-of-principle experiments and to enable large-scale quantum repeater networks, sources emitting at the same energy, on the order of the homogeneous linewidth of the emitters, are required in each node of the network. In combination with spectral fine-tuning, that is key to achieve spectral resonance of multiple single-photon sources within the QD’s homogeneous linewidth of about 1-2 μeV, which has high potential to enable entanglement swapping between remote sources in large-scale quantum repeater networks in the future. We show that piezo strain-tuning can compensate this spectral uncertainty and, promises a scalable route towards large scale quantum networks based on entanglement distribution between quantum light sources with identical emission energy
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