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Register a new userOptical fibre-based (plug-and-play) single photon source using InAsP quantum dot nanowires and gradient-index lens collection
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We present a compact, fibre-coupled single photon source using gradient-index (GRIN) lenses and an InAsP semiconductor quantum dot embedded within an InP photonic nanowire waveguide. A GRIN lens assembly is used to collect photons close to the tip of the nanowire, coupling the light immediately into a single mode optical fibre. The system provides a stable, high brightness source of fibre-coupled single photons. Using pulsed excitation, we demonstrate on-demand operation with a single photon purity of 98.5% when exciting at saturation in a device with a source-fibre collection efficiency of 35% and an overall single photon collection efficiency of 10%. We also demonstrate plug and play operation using room temperature photoluminescence from the InP nanowire for room temperature alignment.
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Single photon sources with high brightness and subnanosecond lifetimes are key components for quantum technologies. Optical nanoantennas can enhance the emission properties of single quantum emitters, but this approach requires accurate nanoscale positioning of the source at the plasmonic hotspot. Here, we use plasmonic nanoantennas to simultaneously trap single colloidal quantum dots and enhance their photoluminescence. The nano-optical trapping automatically locates the quantum emitter at the nanoantenna hotspot without further processing. Our dedicated nanoantenna design achieves a high trap stiffness of 0.6 fN/nm/mW for quantum dot trapping, together with a relatively low trapping power of 2 mW/$mu$m$^2$. The emission from the nanoantenna-trapped single quantum dot shows 7x increased brightness, 50x reduced blinking, 2x shortened lifetime and a clear antibunching below 0.5 demonstrating true single photon emission. Combining nano-optical tweezers with plasmonic enhancement is a promising route for quantum technologies and spectroscopy of single nano-objects.
We demonstrate a spectrally broadband and effcient technique for collecting photoluminescence from a single InAs quantum dot directly into a standard single mode optical fiber. In this approach, an optical fiber taper waveguide is placed in contact with a suspended GaAs nanophotonic waveguide with embedded quantum dots, forming an effcient and broadband directional coupler with standard optical fiber input and output. Effcient photoluminescence collection over a wavelength range of tens of nanometers is demonstrated, and a maximum collection effciency of 6.05 % (corresponding single photon rate of 3.0 MHz) into a single mode optical fiber was estimated for a single quantum dot exciton.
Sources of single photons are key elements in the study of basic quantum optical concepts and applications in quantum information science. Among the different sources available, semiconductor quantum dots excel with their straight forward integrability in semiconductor based on-chip solutions and the potential that photon emission can be triggered on demand. Usually, the photon emission event is part of a cascaded biexciton-exciton emission scheme. Important properties of the emitted photon such as polarization and time of emission are either probabilistic in nature or pre-determined by electronic properties of the system. In this work, we study the direct two-photon emission from the biexciton. We show that emission through this higher-order transition provides a much more versatile approach to generate a single photon. In the scheme we propose, the two-photon emission from the biexciton is enabled by a laser field (or laser pulse) driving the system into a virtual state inside the band gap. From this intermediate virtual state, the single photon of interest is then spontaneously emitted. Its properties are determined by the driving laser pulse, enabling all-optical on-the-fly control of polarization state, frequency, and time of emission of the photon.
Reliable generation of single photons is of key importance for fundamental physical experiments and to demonstrate quantum technologies. Waveguide-based photon pair sources have shown great promise in this regard due to their large degree of spectral tunability, high generation rates and long photon coherence times. However, for such a source to have real world applications it needs to be efficiently integrated with fiber-optic networks. We answer this challenge by presenting an alignment-free source of photon pairs in the telecommunications band that maintains heralding efficiency > 50 % even after fiber pigtailing, photon separation, and pump suppression. The source combines this outstanding performance in heralding efficiency and brightness with a compact, stable, and easy-to-use plug & play package: one simply connects a laser to the input and detectors to the output and the source is ready to use. This high performance can be achieved even outside the lab without the need for alignment which makes the source extremely useful for any experiment or demonstration needing heralded single photons.
A deterministic source of coherent single photons is an enabling device of quantum-information processing for quantum simulators, and ultimately a full-fledged quantum internet. Quantum dots (QDs) in nanophotonic structures have been employed as excellent sources of single photons, and planar waveguides are well suited for scaling up to multiple photons and emitters exploring near-unity photon-emitter coupling and advanced active on-chip functionalities. An ideal single-photon source requires suppressing noise and decoherence, which notably has been demonstrated in electrically-contacted heterostructures. It remains a challenge to implement deterministic resonant excitation of the QD required for generating coherent single photons, since residual light from the excitation laser should be suppressed without compromising source efficiency and scalability. Here, we present the design and realization of a novel planar nanophotonic device that enables deterministic pulsed resonant excitation of QDs through the waveguide. Through nanostructure engineering, the excitation light and collected photons are guided in two orthogonal waveguide modes enabling deterministic operation. We demonstrate a coherent single-photon source that simultaneously achieves high-purity ($g^{(2)}(0)$ = 0.020 $pm$ 0.005), high-indistinguishability ($V$ = 96 $pm$ 2 %), and $>$80 % coupling efficiency into the waveguide. The novel `plug-and-play coherent single-photon source could be operated unmanned for several days and will find immediate applications, e.g., for constructing heralded multi-photon entanglement sources for photonic quantum computing or sensing.
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