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Memory-assisted quantum key distribution resilient against multiple-excitation effects
摘要： Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) has recently been proposed as a technique to improve the rate-versus-distance behavior of QKD systems by using existing, or nearly-achievable, quantum technologies. The promise is that MA-MDI-QKD would require less demanding quantum memories than the ones needed for probabilistic quantum repeaters. Nevertheless, early investigations suggest that, in order to beat the conventional memory-less QKD schemes, the quantum memories used in the MA-MDI-QKD protocols must have high bandwidth-storage products and short interaction times. Among different types of quantum memories, ensemble-based memories offer some of the required specifications, but they typically suffer from multiple excitation effects. To avoid the latter issue, in this paper, we propose two new variants of MA-MDI-QKD both relying on single-photon sources for entangling purposes. One is based on known techniques for entanglement distribution in quantum repeaters. This scheme turns out to offer no advantage even if one uses ideal single-photon sources. By finding the root cause of the problem, we then propose another setup, which can outperform single memory-less setups even if we allow for some imperfections in our single-photon sources. For such a scheme, we compare the key rate for different types of ensemble-based memories and show that certain classes of atomic ensembles can improve the rate-versus-distance behavior.
关键词： quantum cryptography,quantum networks,quantum key distribution (QKD),quantum memory,single-photon source,quantum communications
更新于2025-09-23 15:22:29
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Fluorescence Imaging for Ultrafiltration of Individual Nanoparticles from a Colloidal Solution in Track Membranes
摘要： We have used ? uorescence nanoscopy for direct imaging of adsorption of individual colloidal quantum dots of diameter ~10 nm (spherical core/shell CdSeS/ZnS semiconductor nanocrystals, functionalized by organic oleic acid ligands) in nanopores of a nuclear ? lter (a polypropylene track membrane with pores of diameter ~500 nm). We have shown that when a colloidal toluene solution passes through the pores of the membrane, the nanoparticles are completely retained at a depth of 10 μm.
关键词： nanopore,single-photon source,CdSe,membrane,nanoscopy,entangled-photon source,quantum dot,colloidal solution,microscopy,nanoparticles,ultra? ltration,oleic acid,nuclear ? lter,luminescence,polymer
更新于2025-09-23 15:21:21
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Towards bright and pure single photon emitters at 300 K based on GaN quantum dots on silicon
摘要： Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission at non-cryogenic temperatures due to their large exciton binding energies. Here, we demonstrate GaN QD single photon emitters operating at 300 K with g(2)(0) = 0.17 ± 0.08. At this temperature, single photon emission rates up to 106 s?1 are reached while g(2)(0) ≤ 0.5 is maintained. Our results are achieved for GaN QDs embedded in a planar AlN layer grown on silicon, representing a promising pathway for future interlinkage with optical waveguides and cavities. These samples allow exploring the limiting factors to key performance metrics for single photon sources, such as brightness and single photon purity. While high brightness is assured by large exciton binding energies, the single photon purity is mainly affected by the spectral overlap with the biexcitonic emission. Thus, the performance of a GaN QD as a single photon emitter depends on the balance between the emission linewidth and the biexciton binding energy. Small GaN QDs with an emission energy in excess of 4.2 eV are promising candidates for future room temperature applications, since the biexciton binding energy becomes comparable to the average emission linewidth of around 55 meV.
关键词： single photon source,GaN,room temperature,wide bandgap,quantum dot
更新于2025-09-23 15:21:01
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Design for Hybrid Circular Bragg Gratings for a Highly Efficient Quantum-Dot Single-Photon Source
摘要： We present a design for hybrid circular Bragg gratings (hCBGs) for efficiently extracting single-photons emitted by InAs quantum dots (QDs) embedded in GaAs. Finite-difference time-domain simulations show that a very high photon collection efficiency (PCE) up to 96% over a 50 nm bandwidth and pronounced Purcell factors up to 19 at cavity resonance are obtained. We also systematically investigate the geometry parameters, including the SiO2 thickness, grating period, gap width and the central disk radius, to improve the device performances. Finally, the PCEs and the Purcell factors of QDs located at different positions of the hCBG are studied, and the results show great robustness against uncertainties in the location of the QD.
关键词： Semiconductor quantum dots,Circular Bragg gratings,Single-photon source
更新于2025-09-23 15:21:01
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Analysis of a single-mode waveguide at sub-terahertz frequencies as a communication channel
摘要： We study experimentally the transmission of an electromagnetic waveguide in the frequency range from 160 to 300 GHz. Photo-mixing is used to excite and detect the fundamental TE10 mode in a rectangular waveguide with two orders-of-magnitude lower impedance. The large impedance mismatch leads to a strong frequency dependence of the transmission, which we measure with a high-dynamic range of up to 80 dB and with high frequency-resolution. The modified transmission function is directly related to the information rate of the waveguide, which we estimate to be about 1 bit per photon. We suggest that the results are applicable to a Josephson junction employed as a single-photon source and coupled to a superconducting waveguide to achieve a simple on-demand narrow-bandwidth free-space number-state quantum channel.
关键词： communication channel,TE10 mode,sub-terahertz frequencies,Josephson junction,impedance mismatch,superconducting waveguide,single-photon source,waveguide
更新于2025-09-23 15:19:57
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Controllable movement of single-photon source in multifunctional magneto-photonic structures
摘要： Quantum dot (QD) coupling in nanophotonics has been widely studied for various potential applications in quantum technologies. Micro-machining has also attracted substantial research interest due to its capacity to use miniature robotic tools to make precise controlled movements. In this work, we combine fluorescent QDs and magnetic nanoparticles (NPs) to realize multifunctional microrobotic structures and demonstrate the manipulation of a coupled single-photon source (SPS) in 3D space via an external magnetic field. By employing the low one photon absorption (LOPA) direct laser writing (DLW) technique, the fabrication of 2D and 3D magneto-photonic devices containing a single QD is performed on a hybrid material consisting of colloidal CdSe/CdS QDs, magnetite Fe3O4 NPs, and SU-8 photoresist. Two types of devices, contact-free and in-contact structures, are investigated to demonstrate their magnetic and photoradiative responses. the coupled SPS in the devices is driven by the external magnetic field to perform different movements in a 3D fluidic environment. The optical properties of the single QD in the devices are characterized.
关键词： Quantum dot,direct laser writing,single-photon source,magnetic nanoparticles,magneto-photonic structures
更新于2025-09-23 15:19:57
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Multiplexed Single-Photon Source Based on Multiple Quantum Dots Embedded within a Single Nanowire
摘要： Photonics-based quantum information technologies require efficient, high emission rate sources of single photons. Position-controlled quantum dots embedded within a broadband nanowire waveguide provide a fully scalable route to fabricating highly efficient single photon sources. However, emission rates for single photon devices are limited by radiative recombination lifetimes. Here we demonstrate a multiplexed single photon source based on a multi-dot nanowire. Using epitaxially grown nanowires, we incorporate multiple energy-tuned dots, each optimally positioned within the nanowire waveguide, and providing single photons with high efficiency. This linear scaling of the single photon emission rate with number of emitters is demonstrated using a five-dot nanowire with an average multiphoton emission probability of < 4% when excited at saturation. This represents the first ever demonstration of multiple single photon emitters deterministically incorporated in a single photonic device, and is a major step towards achieving GHz single photon emission rates from a scalable multi-quantum dot system.
关键词： nanowire,single photon source,multiplexing,quantum dot
更新于2025-09-23 15:19:57
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Efficient fiber in-line single photon source based on colloidal single quantum dots on an optical nanofiber
摘要： We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time ( 10.0 ± 0.5 ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimated to be 16 ± 2% with a maximum photon count rate of 1.6 ± 0.2 MHz and a high single photon purity ( g2(0) = 0.11 ± 0.02 ). The device can be easily integrated to the fiber networks paving the way for potential applications in quantum networks.
关键词： quantum dots,single photon source,quantum networks,optical nanofiber,cryogenic temperature
更新于2025-09-19 17:13:59
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High-order actively mode-locked picosecond fiber laser and Poissonian single-photon source
摘要： We propose a novel scheme of high-order actively mode-locked picosecond fiber laser based on the nonlinear polarization rotation in a semiconductor optical amplifier, and experimentally demonstrate the 200th-order mode locking with repetition frequency of ～ 1.19 GHz and pulse width of 1.63 ps. The fundamental repetition frequency is accurately obtained to be 5.9639 MHz by spectrum analysis. Our laser is much easier mode locked and stabler than passive mode-locked ones. Taking advantage of the ultra-stable mode-locked laser, we obtain practical quasi-single-photon (QSP) source. Statistic analyses show that it approaches closer to the Poisson distribution at lower count rate. In our experiment, at count rate of 9.7 kcps or QSP emitting rate of ～97 kcps, it obeys a perfect standard Poisson distribution. The laser is convenient to be upgraded for higher-order mode-locked at repetition frequency over 40 GHz, which are suitable to generate high-speed QSP source for future quantum communications.
关键词： Active mode-locked,Picosecond fiber lasers,Single photon source
更新于2025-09-16 10:30:52
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Improving indistinguishability of single photons from colloidal quantum dots using nanocavities
摘要： Colloidal quantum dots have garnered active research interest as quantum emitters due to their robust synthesis process and straightforward integration with nanophotonic platforms. However, obtaining indistinguishable photons from the colloidal quantum dots at room temperature is fundamentally challenging because they suffer from an extremely large dephasing rate. Here we propose an experimentally feasible method of obtaining indistinguishable single photons from an incoherently pumped solution-processed colloidal quantum dot coupled to a system of nanocavities. We show that by coupling a colloidal quantum dot to a pair of silicon nitride cavities, we can obtain comparable performance of a single photon source from colloidal quantum dots as other leading quantum emitters like defect centers and self-assembled quantum dots.
关键词： Colloidal quantum dots,Nanocavities,Indistinguishable single photon source
更新于2025-09-16 10:30:52