1,720,995 research outputs found
Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission
Full text linkSelf-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30?nm (<10?nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (?3)
Bright Single-Photon Emission From a Quantum Dot in a Circular Bragg Grating Microcavity
No full textBright single-photon emission from single quantum dots (QDs) in suspended circular Bragg grating microcavities is demonstrated. This geometry has been designed to achieve efficient (>50%) single-photon extraction into a near-Gaussian-shaped far-field pattern, modest (≈10×) Purcell enhancement of the radiative rate, and a spectral bandwidth of a few nanometers. Measurements of fabricated devices show progress toward these goals, with collection efficiencies as high as ≈10% demonstrated with moderate spectral bandwidth and rate enhancement. Photon correlation measurements are performed under above-bandgap excitation (pump wavelength = 780 to 820 nm) and confirm the single-photon character of the collected emission. While the measured sources are all antibunched and dominantly composed of single photons, the multiphoton probability varies significantly. Devices exhibiting tradeoffs among collection efficiency, Purcell enhancement, and multiphoton probability are explored and the results are interpreted with the help of finite-difference time-domain simulations. Below-bandgap excitation resonant with higher states of the QD and/or cavity (pump wavelength = 860 to 900 nm) shows a near-complete suppression of multiphoton events and may circumvent some of the aforementioned tradeoffs
Quantum dot single-photon collection increased by metallic nano-rings
No full textBy depositing metallic nano-rings on the surface of GaAs chips containing single InAs quantum dots, we show that single-photon extraction is increased, reaching fluxes as high as 7M photons/s, in a broadband, scalable device
Thermal release tape-assisted semiconductor membrane transfer process for hybrid photonic devices embedding quantum emitters
Full text linkThe ability to combine different materials enables a combination of complementary properties and device engineering that cannot be found or exploited within a single material system. In the realm of quantum nanophotonics, one might want to increase device functionality by, for instance, combining efficient classical and quantum light emission available in III–V semiconductors, low-loss light propagation accessible in silicon-based materials, fast electro-optical properties of lithium niobate, and broadband reflectors and/or buried metallic contacts for local electric field application or electrical injection of emitters. However, combining different materials on a single wafer is challenging and may result in low reproducibility and/or low yield. For instance, direct epitaxial growth requires crystal lattice matching for producing of defect-free films, and wafer bonding requires considerable and costly process development for high bond strength and yield. We propose a transfer printing technique based on the removal of arrays of free-standing membranes and their deposition onto a host material using a thermal release adhesive tape-assisted process. This approach is versatile, in that it poses limited restrictions on the transferred and host materials. In particular, we transfer 190 nm-thick GaAs membranes that contain InAs quantum dots and which have dimensions up to about 260 μm × 80 μm onto a gold-coated silicon substrate. We show that the presence of a back reflector combined with the etching of micropillars significantly increases the extraction efficiency of quantum light from a single quantum dot line, reaching photon fluxes exceeding 8 × 105 photons per second. This flux is four times higher than the highest count rates measured from emitters outside the pillars on the same chip. Given its versatility and ease of processing, this technique provides a path to realising hybrid quantum nanophotonic devices that combine virtually any material in which free-standing membranes can be made onto any host substrate, without specific compatibility issues and/or requirements
Direct-laser-written polymer nanowires for broadband single photon collection from epitaxially-grown quantum dots
No full textPolymer nanowires are fabricated using direct laser writing to collect single photons from epitaxially-grown InAs/GaAs quantum dots, providing broadband out-of-plane waveguiding, emission control, and improved collection efficiency, with limited adverse effect on the underlying devices
Metallic nano-rings for broadband extraction of quantum light
No full textWe show that metallic nano-rings, deposited on the surface of a chip, centered around single InAs/GaAs quantum dots, allow increasing the single-photon flux, reaching 7M photons/s, in a device comprising a ring and gold back-reflector
Broadband, efficient extraction of quantum light by a photonic device comprised of a metallic nano-ring and a gold back reflector
No full textTo implement quantum light sources based on quantum emitters in applications, it is desirable to improve the extraction efficiency of single photons. In particular, controlling the directionality and solid angle of the emission are key parameters, for instance, to couple single photons into optical fibers and send the information encoded in quantum light over long distances, for quantum communication applications. In addition, fundamental studies of the radiative behavior of quantum emitters, including studies of coherence and blinking, benefit from such improved photon collection. Quantum dots grown via Stranski–Krastanov technique have shown to be good candidates for bright, coherent, indistinguishable quantum light emission. However, one of the challenges associated with these quantum light sources arises from the fact that the emission wavelengths can vary from one emitter to the other. To this end, broadband light extractors that do not rely on high-quality factor optical cavities would be desirable, so that no tuning between the quantum dot emission wavelength and the resonator used to increase the light extraction is needed. Here, we show that metallic nano-rings combined with gold back reflectors increase the collection efficiency of single photons, and we study the statistics of this effect when quantum dots are spatially randomly distributed within the nano-rings. We show an average increase in the brightness of about a factor 7.5, when comparing emitters within and outside the nano-rings, in devices with a gold back reflector, and we measure count rates exceeding 7 × 106 photons per second and single photon purities as high as 85% ± 1%. These results are important steps toward the realization of scalable, broadband, easy to fabricate sources of quantum light for quantum communication applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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