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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) - Operational Description of Single-Photon Detectors Including Timing-Jitter Effects
摘要： Discrete variable quantum optics stands as one of the most prominent platform for quantum technologies with an increasing number of encouraging out-of-the-laboratory implementations [1]. The quest for competitive quantum photonic systems, compatible with future engineered systems, has promoted huge developments concerning both source and detection devices [2]. To date, a critical point lies in experiments’ operation rates. Time multiplexing technics allow in principle to pump photonic sources at rates on the order of the GHz [3]. However, a strong limitation to ultra-fast operation lies in timing errors at the detection stage. Limited resolution directly affects the quality of any time-correlated single photon counting or quantum state engineering operations [3]. In particular, single photon detector’s timing-jitters lead counts associated with a given optical clock cycle to appear as temporally indistinguishable from those corresponding to neighbouring ones [2]. Fast and accurate time-tagging is mandatory in multiple operations, such as quantum teleportation [1], quantum state engineering [3] and quantum random number generation. In anticipation to further technological advances, as well as in the perspective of promoting novel conceptual developments on existing quantum communication protocols, it is thus of the utmost importance to correctly describe the effects of detectors’ timing performances. In our work, we explicitly address the problem of detection temporal uncertainties by means of an original theoretical model able to describe the temporal behaviour of standard single photon detectors, with no photon-number resolving abilities [2], affected by non negligible timing-jitter and in presence of dead-time [4]. We consider the case of standard ON/OFF detectors, say detectors with no photon-number resolving abilities [2], and we adopt the formalism of positive operator-valued measurements (POVM) [5]. This approach has already been employed to describe detector with photon-number resolving abilities and has been successfully used to experimentally investigate the characteristics of unknown single photon detectors [6]. Our model exploits a multi-mode formalism to describe temporal degrees of freedom to fully describe timing-resolution effects in ON/OFF detectors by a fully operational POVM description, taking into account the effect of dead-time and finite detection efficiency, without any a priori restriction on the number of photons impinging on the detector. We apply our results to the quantitative study of timing-jitter effects in some usual quantum optics experiments, such as direct photon detection, coincidence measurements, and heralded quantum state preparation. As an example, for a time correlation experiment, considering a source of simultaneous twin photons, our model allows expressing explicitly the delay probability density function. As another example, this fully quantum approach allows expressing the density matrix of a single-photon state obtained in a heralded single-photon generation experiment [3], by taking into account the imperfections of the heralding detector. In conclusion, we believe that our work fills a gap in the discussion on practical quantum technologies by providing a full operational POVM description of practical detection stages, with non negligible timing-jitter and in presence of dead-time. Although we mostly provide simple examples involving one or two photons impinging on the detectors, our formalism is capable of describing general experimental situations. We therefore think that these characteristics stand as a valuable help for a better comprehension of the timing-jitter effect in the perspective of developing ultra-fast quantum communication, including when detector’s timing-jitter is not negligible with respect to repetition period.
关键词： timing-jitter,quantum communication,POVM,quantum optics,single-photon detectors
更新于2025-09-16 10:30:52
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Precise Photon Correlation Measurement of a Chaotic Laser
摘要： The second order photon correlation g(2)(τ) of a chaotic optical-feedback semiconductor laser is precisely measured using a Hanbury Brown–Twiss interferometer. The accurate g(2)(τ) with non-zero delay time is obtained experimentally from the photon pair time interval distribution through a ninth-order self-convolution correction. The experimental results agree well with the theoretical analysis. The relative error of g(2)(τ) is no more than 5‰ within 50 ns delay time. The bunching effect and coherence time of the chaotic laser are measured via the precise photon correlation technique. This technique provides a new tool to improve the accuracy of g(2)(τ) measurement and boost applications of quantum statistics and correlation.
关键词： optical feedback,chaos,quantum optics,photon correlation,photon statistics,semiconductor lasers
更新于2025-09-16 10:30:52
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Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies
摘要： Coupled quantum dots (CQDs) that consist of two InAs QDs stacked along the growth direction and separated by a relatively thin tunnel barrier have been the focus of extensive research efforts. The expansion of available states enabled by the formation of delocalized molecular wavefunctions in these systems has led to significant enhancement of the already substantial capabilities of single QD systems and have proven to be a fertile platform for studying light–matter interactions, from semi-classical to purely quantum phenomena. Observations unique to CQDs, including tunable g-factors and radiative lifetimes, in situ control of exchange interactions, coherent phonon effects, manipulation of multiple spins, and nondestructive spin readout, along with possibilities such as quantum-to-quantum transduction with error correction and multipartite entanglement, open new and exciting opportunities for CQD-based photonic quantum technologies. This review is focused on recent CQD work, highlighting aspects where CQDs provide a unique advantage and with an emphasis on results relevant to photonic quantum technologies.
关键词： quantum information,quantum dots,coupled quantum dots,quantum optics
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) - Coherent Coupling of Single Molecules to Microresonators
摘要： Many interesting proposals in quantum optics and light-matter interaction rely on having multiple quantum emitters well-coupled to a single mode of light. Of particular interest are cases where several identical emitters couple to a one-dimensional (1D) photonic medium. Recently, we presented such a system by evanescent coupling of organic dye molecules to the same guided mode of an on-chip subwavelength waveguide [1]. While this coupling allowed us to demonstrate up to 7.5% transmission extinction of the propagating light by a single molecule, it is still not sufficient for achieving higher-order effects such as photon-mediated interaction of multiple emitters coupled to the same waveguide. One way to improve the waveguide-emitter coupling is the use of resonant structures, as was recently shown in our laboratory for a microscopic open Fabry-Perot cavity [2]. In that work, we demonstrated a strong Purcell broadening of the molecular emission, and almost complete extinction of the resonant cavity transmission. In the current work, we extended this approach to on-chip racetrack resonators [3], as shown in Fig. 1(a). In such a geometry, the coupling enhancement is proportional to the number of photon round trips inside the resonator, which is roughly equal to F/π, where F is the resonator finesse. Currently, our resonators can reach finesse as high as 18 when exposed to the surrounding organic matrix at cryogenic temperatures, leading to enhanced extinction dips up to 22%, as shown in the orange plot in Fig. 1(b). We additionally verify the molecule-resonator coupling by localizing the position of the molecule (marked by a white arrow in Fig. 1(a)), and by observing the expected peak in the transmission port of the resonator (blue line in Fig. 1(b)). Finally, we perform a comparison to a single waveguide on the same chip, which still showed maximal extinction of only 7%, consistent with the previous results. We discuss the observed degree of enhancement, compare it with the predictions of theoretical calculations, and evaluate future strategies for reaching on-chip near-unity coupling efficiency as well as many-emitter effects, such as light localization and generation of polaritonic states [4].
关键词： racetrack resonators,light-matter interaction,waveguide-emitter coupling,photonic medium,quantum optics,Purcell broadening,polaritonic states,resonant structures,Fabry-Perot cavity,quantum emitters
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) - Photon Correlations in PT-Symmetric Waveguide Systems
摘要： Parity-Time (PT)-symmetric systems have been intensely studied since their first description by Bender & Boettcher in 1998 [1]. Especially in photonics, numerous PT-symmetric effects and systems were investigated [2]. However, all of these experiments used classical light or single photons. Here, we present the first observation of two-photon interference in a lossy directional coupler and its associated Hong-Ou-Mandel (HOM) dip. In optics, PT symmetric potentials can be realized by enforcing a symmetric real part of the refractive index and an antisymmetric imaginary part (gain/loss) [3]. Notably, the transition to the quantum-optical regime precludes one from deploying gain [4], thus, we make use of entirely passive systems: By choosing an appropriate loss distribution, the behaviour of the system can be separated into a global loss factor and the desired non-Hermitian dynamics [5]. In this vein, the object of our following considerations is a passive PT-symmetric coupler in which two waveguides interact over a distance z, see Fig. 1 A. Rapid microscopic undulations of the waveguide trajectory serve to introduce effectively constant Markovian losses, resulting in the desired complex index distribution (B). Fig. 1. (A) In a pair of coupled waveguides, rapid undulations introduce bending losses and the (B) effective complex index distribution. (C) Dependence of the two-photon coincidence on the propagation length in the coupler. In contrast to the Hermitian case, PT-symmetry systematically displaces the dip minimum towards shorter propagation lengths, as indicated by the vertical dashed red line. In the experiment (D), corresponding coincidence data were obtained for Hermitian and PT-symmetric couplers. We achieved a dip with a visibility of 87±2 % and the minimum at 3 cm in the Hermitian case, and in the PT case 90±4 % at a position of 2.75 cm. We theoretically describe light propagation in the lossy directional coupler by a quantum master equation in Lindblad form. Our rigorous approach provides information on the full quantum state of the system. It is based on a Lie algebra treatment that provides us with an eigen-decomposition of the density matrix. The analytical solution holds for the unbroken PT-symmetry case, i.e. for losses that do not exceed twice the coupling. The resulting coincidence function for a |1,1> input state is plotted in Fig. 1 C: In the Hermitian case, the HOM dip occurs at exactly half the coupling length. In contrast, the interference minimum occurs after a shorter propagation length in the PT-symmetric system, as the vertical dashed line indicates. For the experiment, a set of lossy directional couplers of identical couplings with different propagation lengths was implemented to sample light at different z positions. A corresponding set of conventional Hermitian couplers served as baseline reference. Our measurements were executed with pairs of indistinguishable photons obtained by type-I spontaneous parametric down conversion, the coincidences at the sample output were recorded by avalanche photo detectors. In conclusion, our theoretical and experimental findings indicate that the asymmetric loss distribution in the PT-symmetric case can systematically accelerate the quantum interference dynamics in comparison to the Hermitian case.
关键词： PT-symmetric systems,two-photon interference,quantum optics,non-Hermitian dynamics,Hong-Ou-Mandel dip
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) - Planar Optical Antennas as Efficient Single-Photon Sources for Free-Space and Fiber-Based Operation in Quantum Optics and Metrology
摘要： Practical implementations of quantum technologies, ranging from optical quantum computing to metrological measurements, suffer from the lack of high-rate, on-demand sources of indistinguishable single photons. We will discuss a simple and versatile planar optical antenna, showing both theoretical and experimental evidence of low-loss (< 20%) beaming of the radiation from a single quantum emitter into a narrow cone of solid angles in free space, which allows in principle up to 50% coupling into a single-mode fiber. In particular, we will first present an experimental implementation of the design operated at room temperature, exploiting Dibenzoterrylene molecules (DBT) hosted in a crystalline anthracene matrix (Ac) [1]. The DBT:Ac system is particularly suitable for this task, due to its outstanding photo-physical properties (i.e. long-term photostability both at room and cryogenic temperature, lifetime-limited emission at cryogenic temperatures, 780 nm operating wavelength) demonstrated in 50 nm-thick crystals [2] and recently also in nanocrystals [3]. Moreover, single photons from DBT molecules and similar [4] result very appealing concerning quantum communication and computation protocols which involve quantum memories, due to the unmatched stability and narrowness of their spectrum (below 100 MHz). Then we will report on our theoretical study to determine the ultimate performances attainable with such design in case of operation in cryogenic environment, exploring materials and fine tuning of geometrical parameters. We will finally discuss our recent results about a single-mirror antenna operating at cryogenic temperature. We demonstrate a photon flux in the Fourier-limited line higher than 1MHz at detectors, and coupling of fluorescence into single-mode fibers up to 46%. These results open to the deploiment of our system both in quantum optics experiments requiring deterministic single-photon sources and in metrology, in particular for a new operative definition of the candela, as recently proposed in the EMPIR project 'SIQUST' [5].
关键词： Quantum Optics,Single-Photon Sources,Dibenzoterrylene molecules,Metrology,Planar Optical Antennas,Crystalline anthracene matrix
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) - 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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Microscale Generation of Entangled Photons without Momentum Conservation
摘要： We report, for the first time, the observation of spontaneous parametric down-conversion (SPDC) free of phase matching (momentum conservation). We alleviate the need to conserve momentum by exploiting the position-momentum uncertainty relation and using a planar geometry source, a 6 μm thick layer of lithium niobate. Nonphase-matched SPDC opens up a new platform on which to investigate fundamental quantum effects but it also has practical applications. The ultrasmall thickness leads to a frequency spectrum an order of magnitude broader than that of phase-matched SPDC. The strong two-photon correlations are still preserved due to energy conservation. This results in ultrashort temporal correlation widths and huge frequency entanglement. The studies we make here can be considered as the initial steps into the emerging field of nonlinear quantum optics on the microscale and nanoscale.
关键词： quantum optics,spontaneous parametric down-conversion,phase matching,lithium niobate,frequency entanglement,momentum conservation
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) - Nonlinear Enhancement with Graphene Heterostructures
摘要： Nonlinear nanoplasmonics provides precise control and manipulation of light. Graphene sustains electrically tunable and long-lived plasmons. By combining these platforms, we observe a 102 enhancement in the third-harmonic generation in graphene heterostructures.
关键词： Nonlinear optics,Plasmonics,Quantum optics
更新于2025-09-11 14:15:04
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Noise filtering for highly correlated photon pairs from silicon waveguides
摘要： We fabricate silicon waveguide spirals and a ring resonator to generate photon pairs based on a spontaneous four-wave mixing. The coincidence-to-accidental-ratio (CAR) of photon pairs from the silicon waveguides is measured up to 400 after a noise-filtering by using the combination of bandpass filters and pump-rejection filters. The CAR is enhanced up to 700 by adding on-chip pump-rejection MZIs. We observe the CAR of the photon pairs from a silicon spiral is highly depending on the wavelength detuning from the pump wavelength. We discuss the noise sources related to the degradation of the CAR based on our experimental results.
关键词： Optical planar waveguides,Integrated optics,Quantum Optics
更新于2025-09-11 14:15:04