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Heralded single-photon and correlated-photon-pair generation via spontaneous four-wave mixing in tapered optical fibers
摘要： We study the generation of frequency nondegenerate correlated photon pairs and heralded single photons via spontaneous four-wave mixing (SFWM) in a series of identical micro- or nano?bers (MNFs). Joint spectral intensity of the biphoton ?eld generated at wavelengths of about 880 and 1310 nm has been measured under excitation by 100-ps laser pulses demonstrating good agreement with the theoretical prediction. The measured zero-time second-order autocorrelation function was about 0.2 when the emission rate of the heralded photons was of 4 Hz. The MNF-based source perfectly matches standard single-mode ?bers, which makes it compatible with the existing ?ber communication networks. In addition, SFWM observation in a series of identical MNFs allows for increasing the generation rate of single photons via spatial multiplexing.
关键词： heralded single photons,spontaneous four-wave mixing,correlated photon pairs,micro- or nano?bers,quantum optical technologies
更新于2025-09-23 15:21:01
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High Quality Entangled Photon Pair Generation in Periodically Poled Thin-Film Lithium Niobate Waveguides
摘要： A thin-film periodically poled lithium niobate waveguide was designed and fabricated which generates entangled photon pairs at telecommunications wavelengths with high coincidences-to-accidentals counts ratio CAR > 67000, two-photon interference visibility V > 99%, and heralded single-photon autocorrelation g(0) < 0.025. Nondestructive in situ diagnostics were used to determine the poling quality in 3D. Megahertz rates of photon pairs were generated by less than a milliwatt of pump power, simplifying the pump requirements and dissipation compared to traditional spontaneous parametric down-conversion lithium niobate devices.
关键词： lithium niobate waveguides,quantum information processing,entangled photon pairs,telecommunications wavelengths
更新于2025-09-23 15:19:57
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All-photonic quantum teleportation using on-demand solid-state quantum emitters
摘要： All-optical quantum teleportation lies at the heart of quantum communication science and technology. This quantum phenomenon is built up around the nonlocal properties of entangled states of light that, in the perspective of real-life applications, should be encoded on photon pairs generated on demand. Despite recent advances, however, the exploitation of deterministic quantum light sources in push-button quantum teleportation schemes remains a major open challenge. Here, we perform an important step toward this goal and show that photon pairs generated on demand by a GaAs quantum dot can be used to implement a teleportation protocol whose fidelity violates the classical limit (by more than 5 SDs) for arbitrary input states. Moreover, we develop a theoretical framework that matches the experimental observations and that defines the degree of entanglement and indistinguishability needed to overcome the classical limit independently of the input state. Our results emphasize that on-demand solid-state quantum emitters are one of the most promising candidates to realize deterministic quantum teleportation in practical quantum networks.
关键词： GaAs quantum dot,entangled photon pairs,quantum emitters,quantum teleportation,quantum communication
更新于2025-09-23 15:19:57
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Highly uniform and symmetric epitaxial InAs quantum dots embedded inside Indium droplet etched nanoholes
摘要： III?V semiconductor quantum dots (QDs) obtained by local droplet etching technology provide a material platform for generation of non-classic light. However, using this technique to fabricate single emitters for a broad spectral range remains a signi?cant challenge. Herein, we successfully extend the QD emission wavelength to 850–880 nm via highly uniform and symmetric InAs QDs located inside indium-droplet-etching nanoholes. The evolution of InGaAs nanostructures by high temperature indium droplet epitaxy on GaAs substrate is revealed. By carefully designing the appropriate growth conditions, symmetric QDs with the a small ?ne structure splitting of only ～4.4?±?0.8 μeV are demonstrated. Averaging over the emission energies of 32 QDs, an ensemble broadening of 12 meV is observed. Individual QDs are shown to emit nonclassically with clear evidence of photon antibunching. These highly uniform and symmetric nanostructures represent a very promising novel strategy for quantum information applications.
关键词： entangled photon pairs,symmetric quantum dots,droplet etched nanoholes,molecular beam epitaxy
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Tailored Spontaneous Four-Wave Mixing in Sinusoidally-Tapered Fibres
摘要： Quasi-phase-matching periodically-tapered waveguides (PTWs) can enable efficient on-demand third-order parametric interactions using right combinations of the tapering period and modulation amplitude. Similar to periodically-poled ferroelectric crystals, this new technique eliminates the stringent constraints imposed by conventional methods on the frequencies, mode profiles, and polarisations of the interacting photons. An example of PTWs is the sinusoidally-tapered fibres that have been exploited in manipulating supercontinuum generation and modulation instability. In this work, I have developed a rigorous quantum model to investigate spontaneous four-wave mixing (SFWM) inside these tapered waveguides. The right combinations between the modulation amplitude ?d and tapering period ΛT that enhances the expected number of photons N?s at the targeted wavelengths are portrayed in Fig.1(a), for fibres with same number of periods M. The values of N?s are normalised to the case when ?d=0, to quantify the enhancement in photon-pairs generation using the PTW-technique in comparison to uniform fibres. For only M=50, N?s is remarkably enhanced by 35dB. The output spectrum of the photon-pairs is featured as a narrow sinc-function with very weak sidelobes that are significantly diminished for large number of periods, as depicted in Fig.1(b). The 2D representation of the spectrum as a function of the photon-pairs wavelengths (λs, λi) is shown in panel (c). In this plot, the pump is assumed to be a monochromatic at a frequency satisfies the energy conservation. The corresponding N?s for a Gaussian-pulse pump source with an input energy 1nJ and a full-width-half-maximum 4ps is portrayed in analysis, Fig.1(d). Using the Schmidt decomposition, the spectral-purity is 0.74. This shows the ability of the PTW-technique in producing highly-efficient relatively-pure single photons at any on-demand frequencies without applying any bandpass filters. This work will also open a new direction of research to investigate how the tapering patterns can be fully optimised to tailor the spectral properties of the output photons in third-order nonlinear guided structures.
关键词： spectral-purity,Quasi-phase-matching,spontaneous four-wave mixing,periodically-tapered waveguides,photon-pairs generation
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Time-Energy Entangled Photon Pairs from Doppler-Broadened Atomic Ensemble Via Collective Two-Photon Coherence
摘要： We experimentally demonstrate two-photon interference between a time-energy entangled photon pair generated from Doppler-broadened cascade-type 87Rb atoms using an unbalanced Michelson interferometer. In our system, the CW-mode time-energy entangled photon-pair sources are generated via the SFWM process and the collective two-photon coherence effect of a Doppler-broadened cascade-type atomic ensemble. The coherence time of the two-photon state from the Doppler-broadened atomic ensemble is more than 100 times longer than that of the single-photon state. We investigate two-photon interference (TPI) by means of highly time-resolved coincidence detection and determine the two-photon coherence length of a photon pair from the Doppler-broadened atomic ensemble. We observed fourth-order interference with visibility as high as 97% with the time-energy entangled CW-mode photon pairs from the atomic ensemble for the first time.
关键词： Doppler-Broadened Atomic Ensemble,Quantum Optics,Time-Energy Entangled Photon Pairs,Collective Two-Photon Coherence,Two-Photon Interference
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - The Role of Detector Position in Quantum Ghost Diffraction
摘要： Quantum ghost diffraction enables the measurement of the spatial diffraction pattern of an object without measuring the spatial distribution of the photons that actually interacted with the object [1]. It uses photon pairs generated e.g. by spontaneous parametric down conversion (SPDC) in a nonlinear optical crystal, and relies on the correlation of the generated signal and idler photons in their spatial and temporal degrees of freedom. This measurement scheme is sketched in Fig. 1 (a). After the source, the two photons are separated into two different paths. The object, here we consider a grating, is located only in the signal path and thus interacts only with the signal photons. To measure the diffraction pattern, two detectors of small cross sections are used in the signal and idler arms. The signal detector is usually at a fixed position, collecting photons that interacted with the object. The idler detector can have varying positions, allowing to spatially resolve the collected photons that never interacted with the object. Through measuring the two-photon coincidence counting rate (cid:1842), there exists the potential for recovering the diffraction pattern of the object, which allows to retrieve the grating period.
关键词： Quantum ghost diffraction,diffraction pattern,spatial correlation,photon pairs
更新于2025-09-12 10:27:22
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Biphoton shaping with cascaded entangled-photon sources
摘要： Quantum entanglement is an integral part of quantum optics and has been exploited in areas such as computation, cryptography and metrology. The entanglement between photons can be present in various degrees of freedom (DOFs), and even the simplest bi-partite systems can occupy a large Hilbert space. Therefore, it is desirable to exploit this multi-dimensional space for various quantum applications by fully controlling the properties of the entangled photons in multiple DOFs. While current entangled-photon sources are capable of generating entanglement in one or more DOFs, there is currently a lack of practical techniques that can shape and control the entanglement properties in multiple DOFs. Here we show that cascading two or more entangled-photon sources with tunable linear media in between allows us to generate photon-pairs whose entanglement properties can be tailored and shaped in the frequency and polarisation domains. We first develop a quantum mechanical model to study the quantum state generated from the cascade structure with special considerations paid to the effects of pump temporal coherence, linear dispersion, and in-structure polarisation transformation applied between the entangled-photon sources. We then experimentally generate photon-pairs with tunable entanglement properties by manipulating the dispersion and birefringence properties of the linear medium placed in between two entangled-photon sources. This is done in an all-fibre, phase stable, and alignment-free configuration. Our results show that the cascade structure offers a great deal of flexibility in tuning the properties of entangled photons in multiple DOFs, opening up a new avenue in engineering quantum light sources.
关键词： nonlinear interferometer,photon-pairs,frequency and polarisation domains,cascade structure,Quantum entanglement
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Conversion of two Photons with Different Color by a Single Waveguide for Quantum Networks
摘要： Quantum communication would enable opportunities such as secure communication. A quantum network with quantum nodes and quantum channels is necessary for this. The realization of such a quantum network requires the ability to process, store and send photons over long distances. It is not very likely that a single physical system can accomplish all these operations. Therefore, dissimilar quantum systems have to be connected in future quantum networks. Quantum channels are likely to be based on the existing fiber network because it is already well established. The fiber network operates at telecom wavelength (1550 nm) since the losses in fibers are minimal at this wavelength. That is why quantum states at telecom wavelength are needed. Unfortunately, suitable single photon sources and quantum memories are not available at telecom wavelength. Frequency conversion provides the possibility to alter the wavelength of a single photon to another wavelength. With frequency conversion it is possible to convert the VIS/NIR single photon to telecom wavelength and transfer the state over long distances. However, quantum networks do not require single photons but rather entangled photon pairs. Quantum dots are able to generate entangled photon pairs via a biexciton cascade emission. The emitted photons of a cascaded emission usually have slightly different wavelengths. The frequency conversion of the entangled photon pair on a single device would be advantageous for building quantum nodes for real life applications. We present a frequency conversion based on a single lithium niobate waveguide with different local temperatures to convert two different wavelengths on the same chip. The setup consists of a 2100 nm pump laser and a fiber coupled input port for the two biexciton photons (894 nm and 892 nm). These three wavelengths are focused by a lens into a nonlinear crystal with two different local temperatures. Each segment converts one of the incoming wavelengths. The converted signal is coupled into an optical fiber and guided to a filter system, which removes remaining pump light and generated noise photons. A proof of principle experiment was performed with attenuated laser light, where the converted spectrum is shown.
关键词： lithium niobate waveguide,frequency conversion,Quantum communication,entangled photon pairs,quantum network
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Integrated Semiconductor Quantum Photonics
摘要： For fundamental tests of quantum physics as well as for quantum communications, non-classical states of light are an important tool. In this talk, we will present our work on developing nonlinear AlGaAs waveguides into a platform for quantum photonics in semiconductors. Most III-V semiconductors exhibit a large second-order optical nonlinearity, but phase-matching the nonlinear interaction is notoriously difficult. As a solution Bragg-reflection waveguides allow efficient creation of photon pairs through spontaneous parametric down-conversion. They have the potential to be homogeneously integrated with a pump laser and passive and active components on the chip. In our waveguides, we can create high-fidelity polarization [1] and time-bin entangled [2] photon pairs, which cover a large frequency band in the low-loss telecommunication window, suitable for serving multiple users through wavelength division multiplexing. For all our applications, it is important that we can design the desired linear and nonlinear properties, which in turn makes precise characterization necessary. For this purpose, we have developed a Fourier-transform Fabry-Perot spectroscopy technique [3], which yields the relevant device parameters with superior accuracy. We will further present our results on devices that integrate electrically injected lasers and the nonlinear conversion. A layer of quaternary quantum dots acts as the gain medium in a Fabry-Perot waveguide laser, which lases at room temperature in the Bragg mode, i.e. the pump mode for creating photon pairs. We will close with an outlook on further device integration towards a complete semiconductor quantum photonics platform.
关键词： AlGaAs waveguides,photon pairs,Bragg-reflection waveguides,quantum photonics,Fourier-transform Fabry-Perot spectroscopy,spontaneous parametric down-conversion
更新于2025-09-11 14:15:04