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Scientific Reports

All-Optical Fiber Hanbury Brown & Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot

Guillermo Muñoz‐Matutano, David Barrera, Carlos R. Fernández‐Pousa, Raquel Chuliá-Jordán, L. Seravalli, Giovanna Trevisi, Paola Frigeri, Salvador Sales, Juan P. Martínez‐Pastor

Published Jun 3, 2016• 38 citations
Publisher

Abstract

New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 μeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown &Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.

DOI
10.1038/srep27214

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New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 μeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown &Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.
We first succeeded in generating single-photon pulses in the C-band (1.55-µm band: the highest transmittance in optical telecommunication bands) from a single InAs/InP quantum dot. The quantum dot with 1546.1-nm exciton emission was prepared by controlling the growth conditions. A well-designed mesa structure presented efficient injection of the emitted photons into a single-mode optical fiber. A Hanbury-Brown and Twiss measurement has proved that the photons through the fiber were single photons. We also performed to transmit single-photon pulses through 30-km optical fiber. This preliminary trial is a milestone toward quantum telecommunication using ideal single photons.
Abstract Long-distance quantum communication and computation is based on the exchange of information via photons as flying qubits. In all foreseen implementations, from quantum relays and networks to remote quantum computing, the photons must be able to propagate over long distances, in silica fibers, with limited absorption and wave packet dispersion. When propagating into silica fibers, photons in the so-called telecom C-band (i.e. wavelength around 1550 nm) will experience the absolute minimum of absorption, together with a limited photon wave packet dispersion. This implies that losses of information will be minimized and additionally, the capability of the photons to quantum interfere (the so-called Hong–Ou–Mandel effect) will be negligibly affected. This motivated the search for efficient non-classical light sources in this wavelength range. In the present review, we discuss the approaches followed to red-shift the emission wavelength from the near-infrared (NIR) to telecom wavelengths. In particular, the use of metamorphic buffers (MMBs) enabled the use of highly developed InAs/GaAs systems, engineering the dots to emit single and entangled photons in the telecom C-band. The main advantage of this approach is set by the choice of the material system: being the same as state-of-the-art structures emitting in the NIR range, it opens the possibility of achieving comparable performances even at telecommunication wavelengths. Here we will discuss the current state-of-the-art in the generation of non-classical photons, comparing the properties and performances of MMB-based results with other competing quantum dot (QD) platforms. We report in particular that very low fine-structure splitting can be observed with conservative values, on average well below 10 μ eV. This allowed for the observation of post-selected entanglement fidelity higher than 0.6. Additionally, on-demand single-photon emission with g ( 0 ) 2 = 0.184 ± 0.002 was observed in addition to a very low emitter density of ≈ 10 7 cm − 2 and a decay time of τ ≈ 1.2 ns comparable to standard InAs QDs emitting in the NIR range. A final highlight on approaches to further improve the current device performances will also be reported.
Single-photon sources based on quantum dots have been shown to exhibit almost ideal properties such as high brightness and purity in terms of clear anti-bunching as well as high two-photon interference visibilities of the emitted photons, making them promising candidates for different quantum information applications such as quantum computing, quantum communication and quantum teleportation. However, as most single-photon sources also quantum dots typically emit light at wavelengths of electronic transitions within the visible or the near infrared range. In order to establish quantum networks with remote building blocks, low-loss single photons at telecom wavelengths are preferable, though. Despite recent progress on emitters of telecom-photons, the most efficient single-photon sources still work at shorter wavelengths. On that matter, quantum frequency down-conversion, being a nonlinear optical process, has been used in recent years to alter the wavelength of single photons to the telecom wavelength range while conserving their nonclassical properties. Characteristics such as lifetime, first-order coherence, anti-bunching and entanglement have been shown to be conserved or even improved due to background suppression during the conversion process, while the conservation of indistinguishability was yet to be shown. Here we present our experimental results on quantum frequency down-conversion of single photons emitted by an InAs/GaAs quantum dot at 903.6 nm following a pulsed excitation of a p-shell exciton at 884 nm. The emitted fluorescence photons are mixed with a strong pump-field at 2155 nm inside a periodically poled lithium niobate ridge waveguide and converted to 1557 nm. Common issues of a large background due to Raman-scattered pump-light photons spectrally overlapping with the converted single photons could largely be avoided, as the pump-wavelength was chosen to be fairly longer than the target wavelength. Additional narrowband spectral filtering at the telecom regime as a result of the small conversion bandwidth and using a high-performance fiber-Bragg-grating solely left the detector dark counts as the only noise source in our setup. Therefore, we could achieve conversion efficiencies of more than 20 %. In order to test the indistinguishability, sequentially emitted photons were fed into a Mach-Zehnder interferometer and spatially as well as temporally overlapped at the output beam splitter. Cross-correlation measurements between both output-ports of the beam splitter exhibit two-photon interference contrasts of more than 40 % prior to and after the down-conversion step. Accordingly, we demonstrate that the process of quantum frequency conversion preserves photon indistinguishability and can be used to establish a versatile source of indistinguishable single photons at the telecom C-Band. Furthermore our scheme allows for converting photons in a wavelength band from 900 nm to 910 nm to the same telecom target wavelength. This enables us to test indistinguishability of frequency-converted photons, originally stemming from different sources with dinstinguishable wavelengths.
Semiconductor quantum dots emitting in the telecommunication O- and C-bands are promising candidates as single-photon sources for fiber-based quantum communication. In this work, we show how coherent quasi-resonant and phonon-assisted excitation help reveal the intrinsic optical properties of InAs quantum dots embedded in relaxed InGaAs matrices on top of metamorphic InGaAs layers for achieving emission in the telecom bands. By systematically comparing excitation schemes, we separate excitation-induced effects from intrinsic emitter properties. This allows us to observe linewidths as narrow as 21 μμμeV, the disappearance of slow decay channels, and single-photon purity reaching second-order autocorrelation values in the order of 10−210^{-2}10−2. Photoluminescence excitation reveals higher excited states, enabling coherent control of trion transitions and the observation of Rabi-like oscillations in both telecom bands. These results confirm the promising potential of these quantum dots for applications in quantum technologies.
Bright fiber-coupled single photon sources are essential components for practical quantum network. In this work, we present a bright single photon source based on an InAs/InP quantum dot emitting at telecom wavelengths. We designed a nanobeam with a photonic crystal mirror at the other end and a tapered coupler at the other end enabling both directional emission and gaussian-like far-field profile. We detected fiber-coupled single photon count rate of 1.1 MHz with 40 MHz pumping rate. Considering losses from optics and spectral filters, we achieved collection efficiency into first lens of 68% and a total fiber collection efficiency of 8.2%.
The well-established silicon-on-insulator platform is very promising for large-scale integrated photonic and quantum photonic technologies due to the mature manufacturing technology and integration density. Here, we present an efficient and stable fiber-to-chip coupling, which enables the injection of single photons from telecom quantum dots into a silicon-on-insulator photonic chip. Two additional fibers further couple the chip to single-photon detectors. The approach chosen to achieve steady fiber-chip coupling is based on the use of grating couplers steadily packaged with angled single-mode fibers. Using this technique, coupling efficiencies between the fiber and the SOI chip as high as 69.1% per grating coupler (including the taper losses) are reached. The effective interface between the quantum light generated by quantum dots and the silicon components is verified via the measurement of the second-order correlation function using a Hanbury–Brown and Twiss setup. With g(2)(0)=0.051±0.001, it clearly proves the single-photon nature of the injected QD photons. This demonstrates the reliability of the interfacing method and opens the route to employ telecom quantum dots as non-classical light sources with high complexity silicon photonic functionalities.