On-demand Source Research Articles

Oscillating photonic Bell state from a semiconductor quantum dot for quantum key distribution

An on-demand source of bright entangled photon pairs is desirable for quantum key distribution (QKD) and quantum repeaters. The leading candidate to generate such pairs is based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, its pair extraction efficiency is limited to 0.1% when operating at near-unity fidelity due to multiphoton emission at high brightness. Quantum dots in photonic nanostructures can in principle overcome this limit, but the devices with high entanglement fidelity (99%) have low pair extraction efficiency (0.01%). Here, we show a measured peak entanglement fidelity of 97.5% ± 0.8% and pair extraction efficiency of 0.65% from an InAsP quantum dot in an InP photonic nanowire waveguide. We show that the generated oscillating two-photon Bell state can establish a secure key for peer-to-peer QKD. Using our time-resolved QKD scheme alleviates the need to remove the quantum dot energy splitting of the intermediate exciton states in the biexciton-exciton cascade.

On-demand single-electron source via single-cycle acoustic pulses

On-demand single-electron source via single-cycle acoustic pulses

A Neural Radiance Field-Based Architecture for Intelligent Multilayered View Synthesis

A mobile ad hoc network is made up of a number of wireless portable nodes that spontaneously come together en route for establish a transitory network with no need for any central management. A mobile ad hoc network (MANET) is made up of a sizable and reasonably dense community of mobile nodes that travel across any terrain and rely solely on wireless interfaces for communication, not on any well before centralized management. Furthermore, routing be supposed to offer a method for instantly delivering data across a network between any two nodes. Finding the best packet routing from across infrastructure is the major issue, though. The proposed protocol's major goal is to identify the least-expensive nominal capacity acquisition that assures the transportation of realistic transport that ensures its durability in the event of any node failure. This study suggests the Optimized Route Selection via Red Imported Fire Ants (RIFA) Strategy as a way to improve on-demand source routing systems. Predicting Route Failure and energy Utilization is used to pick the path during the routing phase. Proposed work assess the results of the comparisons based on performance parameters like as energy usage, packet delivery rate (PDR), and end-to-end (E2E) delay. The outcome demonstrates that the proposed strategy is preferable and increases network lifetime while lowering node energy consumption and typical E2E delay under the majority of network performance measures and factors.

An on-demand source of energy-entangled electrons using levitons

We propose a source of purely electronic energy-entangled states implemented in a solid-state system with potential applications in quantum information protocols based on electrons. The proposed device relies on the standard tools of electron quantum optics and exploits entanglement of the Cooper pairs of a BCS superconductor. The latter is coupled via an adjustable quantum point contact to two opposite spin-polarized electron wave-guides, which are driven by trains of Lorentzian pulses. This specific choice for the drive is crucial to inject purely electronic entangled states devoid of spurious electron–hole pairs. In the Andreev regime, a perturbative calculation in the tunnel coupling confirms that entangled electrons states are generated at the output of the normal side. For arbitrary tunnel coupling and for a periodic drive, direct current and noise (auto and cross correlations) are computed numerically using a Keldysh–Nambu–Floquet formalism. Importantly, for a periodic drive, the production of these states can be controlled in time, thus implementing an on-demand source of entangled states. We exploit realistic experimental parameters for our device to identify its optimal functioning point.

Widely Tunable Single-Photon Frequency Conversion in a Nanomechanically Reconfigurable Si-Rich Nitride Waveguide

An on-demand single-photon source based on self-assembled semiconductor quantum dots (QDs) is a key building block for quantum communication and quantum information processing. To scale up, a challenge lies in frequency converting the emitted photons to the telecom wavelengths and eliminating the wavelength difference between multiple QDs. In this paper, we propose a novel nanomechanical silicon-rich nitride waveguide device, which can be reconfigured to realize efficient frequency conversion from the emission wavelength band of InAs/GaAs quantum dots at 900 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 950 nm to the telecom C-band around 1550 nm, by exploiting the Bragg scattering process in nonlinear four-wave mixing. Numerical results show that an optimal conversion efficiency over 99% and a signal-to-noise ratio up to 27 dB can be achieved when the waveguide loss is negligible, and the efficiency only reduces to 78% when a realistic loss of 1 dB/cm is considered. We conduct a detailed study on the unwanted noise processes, and provide design guidelines to improve the conversion efficiency and suppress the noises, e.g., by optimizing the power and wavelength of the pump laser.

Characterization and Function of Cryopreserved Bone Marrow from Deceased Organ Donors: A Potential Viable Alternative Graft Source

Despite the readily available graft sources for allogeneic hematopoietic cell transplantation (alloHCT), a significant unmet need remains in the timely provision of suitable unrelated donor grafts. This shortage is related to the rarity of certain HLA alleles in the donor pool, nonclearance of donors owing to infectious disease or general health status, and prolonged graft procurement and processing times. An alternative hematopoietic progenitor cell (HPC) graft source obtained from the vertebral bodies (VBs) of deceased organ donors could alleviate many of the obstacles associated with using grafts from healthy living donors or umbilical cord blood (UCB). Deceased organ donor-derived bone marrow (BM) can be preemptively screened, cryogenically banked for on-demand use, and made available in adequate cell doses for HCT. We have developed a good manufacturing practice (GMP)-compliant process to recover and cryogenically bank VB-derived HPCs from deceased organ donor (OD) BM. Here we present results from an analysis of HPCs from BM obtained from 250 deceased donors to identify any substantial difference in composition or quality compared with HPCs from BM aspirated from the iliac crests of healthy living donors. BM from deceased donor VBs was processed in a central GMP facility and packaged for cryopreservation in 5% DMSO/2.5% human serum albumin. BM aspirated from living donor iliac crests was obtained and used for comparison. A portion of each specimen was analyzed before and after cryopreservation by flow cytometry and colony-forming unit potential. Bone marrow chimerism potential was assessed in irradiated immunocompromised NSG mice. Analysis of variance with Bonferroni correction for multiple comparisons was used to determine how cryopreservation affects BM cells and to evaluate indicators of successful engraftment of BM cells into irradiated murine models. The t test (with 95% confidence intervals [CIs]) was used to compare cells from deceased donors and living donors. A final dataset of complete clinical and matched laboratory data from 226 cryopreserved samples was used in linear regressions to predict outcomes of BM HPC processing. When compared before and after cryopreservation, OD-derived BM HPCs were found to be stable, with CD34+ cells maintaining high viability and function after thawing. The yield from a single donor is sufficient for transplantation of an average of 1.6 patients (range, 1.2 to 7.5). CD34+ cells from OD-derived HPCs from BM productively engrafted sublethally irradiated immunocompromised mouse BM (>44% and >67% chimerism at 8 and 16 weeks, respectively). Flow cytometry and secondary transplantation confirmed that OD HPCs from BM is composed of long-term engrafting CD34+CD38-CD45RA-CD90+CD49f+ HSCs. Linear regression identified no meaningful predictive associations between selected donor-related characteristics and OD BM HPC quality or yield. Collectively, these data demonstrate that cryopreserved BM HPCs from deceased organ donors is potent and functionally equivalent to living donor BM HPCs and is a viable on-demand graft source for clinical HCT. Prospective clinical trials will soon commence in collaboration with the Center for International Blood and Marrow Research to assess the feasibility, safety, and efficacy of Ossium HPCs from BM (ClinicalTrials.gov identifier NCT05068401).

Comparing Experts and Novices for AI Data Work: Insights on Allocating Human Intelligence to Design a Conversational Agent

Many AI system designers grapple with how best to collect human input for different types of training data. Online crowds provide a cheap on-demand source of intelligence, but they often lack the expertise required in many domains. Experts offer tacit knowledge and more nuanced input, but they are harder to recruit. To explore this trade off, we compared novices and experts in terms of performance and perceptions on human intelligence tasks in the context of designing a text-based conversational agent. We developed a preliminary chatbot that simulates conversations with someone seeking mental health advice to help educate volunteer listeners at 7cups.com. We then recruited experienced listeners (domain experts) and MTurk novice workers (crowd workers) to conduct tasks to improve the chatbot with different levels of complexity. Novice crowds perform comparably to experts on tasks that only require natural language understanding, such as correcting how the system classifies a user statement. For more generative tasks, like creating new lines of chatbot dialogue, the experts demonstrated higher quality, novelty, and emotion. We also uncovered a motivational gap: crowd workers enjoyed the interactive tasks, while experts found the work to be tedious and repetitive. We offer design considerations for allocating crowd workers and experts on input tasks for AI systems, and for better motivating experts to participate in low-level data work for AI.

On-Demand Source of Dual-Rail Photon Pairs Based on Chiral Interaction in a Nanophotonic Waveguide

Entanglement is the fuel of advanced quantum technology, enabling, e.g., measurement-based quantum computing and loss-tolerant encoding of quantum information. In photonics, entanglement has traditionally been generated probabilistically, requiring massive multiplexing for scaling up to many photons. An alternative approach utilizing quantum emitters in nanophotonic devices can realize deterministic generation of entangled photons. However, such sources generate polarization entanglement that is incompatible with spatial dual-rail qubit encoding employed in scalable photonic quantum-computing platforms utilizing integrated circuits. Here we propose and experimentally realize an on-demand source of dual-rail photon pairs using a quantum dot in a planar nanophotonic waveguide. The source exploits the cascaded decay of a biexciton state and chiral light-matter coupling to achieve deterministic generation of spatial dual-rail Bell pairs with the amount of entanglement determined by the chirality. The operational principle can readily be extended to multiphoton entanglement generation required for efficient preparation of resource states for photonic quantum computing.Received 17 January 2022Revised 22 May 2022Accepted 8 June 2022DOI:https://doi.org/10.1103/PRXQuantum.3.020363Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhotonic crystalsPhotonicsQuantum communicationQuantum correlations in quantum informationQuantum entanglementSingle photon sourcesPhysical SystemsQuantum dotsWaveguidesPropertiesChiral symmetryAtomic, Molecular & OpticalQuantum Information

Aldh2 is a lineage-specific metabolic gatekeeper in melanocyte stem cells.

ABSTRACTMelanocyte stem cells (McSCs) in zebrafish serve as an on-demand source of melanocytes during growth and regeneration, but metabolic programs associated with their activation and regenerative processes are not well known. Here, using live imaging coupled with scRNA-sequencing, we discovered that, during regeneration, quiescent McSCs activate a dormant embryonic neural crest transcriptional program followed by an aldehyde dehydrogenase (Aldh) 2 metabolic switch to generate progeny. Unexpectedly, although ALDH2 is well known for its aldehyde-clearing mechanisms, we find that, in regenerating McSCs, Aldh2 activity is required to generate formate – the one-carbon (1C) building block for nucleotide biosynthesis – through formaldehyde metabolism. Consequently, we find that disrupting the 1C cycle with low doses of methotrexate causes melanocyte regeneration defects. In the absence of Aldh2, we find that purines are the metabolic end product sufficient for activated McSCs to generate progeny. Together, our work reveals McSCs undergo a two-step cell state transition during regeneration, and that the reaction products of Aldh2 enzymes have tissue-specific stem cell functions that meet metabolic demands in regeneration.

Using the Autler-Townes and ac Stark effects to optically tune the frequency of indistinguishable single photons from an on-demand source

We describe how a coherent optical drive that is near resonant with the upper rungs of a three-level ladder system, in conjunction with a short-pulse excitation, can be used to provide a frequency-tunable source of on-demand single photons. Using an intuitive master equation model, we identify two distinct regimes of device operation: (i) for a resonant drive, the source operates using the Autler-Townes effect, and (ii) for an off-resonant drive, the source exploits the ac Stark effect. The former regime allows for a large frequency-tuning range but coherence suffers from timing jitter effects, while the latter allows for high indistinguishability and efficiency, but with a restricted tuning bandwidth due to high required drive strengths and detunings. We show how both these negative effects can be mitigated by using an optical cavity to increase the collection rate of the desired photons. We apply our general theory to semiconductor quantum dots, which have proven to be excellent single-photon sources, and find that scattering of acoustic phonons leads to excitation-induced dephasing and increased population of the higher-energy level which limits the bandwidth of frequency tuning achievable while retaining high indistinguishability. Despite this, for realistic cavity and quantum dot parameters, indistinguishabilities of over $90%$ are achievable for energy shifts of up to hundreds of $\ensuremath{\mu}\mathrm{eV}$, and near-unity indistinguishabilities for energy shifts up to tens of $\ensuremath{\mu}\mathrm{eV}$. Additionally, we clarify the often-overlooked differences between an idealized Hong-Ou-Mandel two-photon interference experiment and its usual implementation with an unbalanced Mach-Zehnder interferometer, pointing out the subtle differences in the single-photon visibility associated with these different setups.

Microscopic theory of photoassisted electronic transport in normal-metal/BCS-superconductor junctions

We investigate photoassisted electronic transport in a normal-metal/BCS-superconductor junction with a microscopic Hamiltonian approach, for several types of periodic voltage drives applied on the normal-metal side. The time-dependent current and the photoassisted noise are computed to all orders of the tunneling Hamiltonian using a Keldysh-Nambu-Floquet approach. An excess noise analysis allows one to determine to what extent pure electronic excitations with a small number of electrons per period can be generated by the different drives. When the superconducting gap is small compared to the drive frequency, the junction behaves like a normal-metal junction and minimal excess noise is reached for Lorentzian voltage drives carrying an integer charge (levitons). In the opposite regime of a large gap, the excess noise vanishes for half-quantized levitons, giving rise to the perfect transmission of a Cooper pair on the superconducting side. This microscopic approach also allows us to address the intermediate regime, when the drive frequency is comparable to the gap, allowing us to study the nontrivial interplay between Andreev reflection and quasiparticle transfer processes. Our analysis also shows the appearance of Tien-Gordon--type relations connecting the current and noise in the AC-driven junction to their DC counterpart, which we investigate in details. Finally, the possibility to build a reliable on-demand source of Cooper pairs with this setup is examined using realistic experimental parameters.

Application security automation in development

Automated security services can provide on-demand resources that are easily adopted by development teams. To save time and money, application security should be incorporated as early as possible in the application development process. Security requirements are the earliest opportunity to build a secure foundation. Using automation, security requirements can be aligned to system and project attributes and used as a foundation for additional security activities such as secure coding examples and security testing. Later in the development process, automated testing services provide development teams with vulnerability scanning options, depending on whether legacy or modern development practices are used. Legacy development projects can benefit from on-demand source code scanning that does not require tool set-up or configuration. Modern development processes are a better fit for incorporating security testing in automated build-and-test pipelines using working example scripts. When created with development team needs in mind, automated application security services can be valuable resources for development teams that drive better security outcomes. This paper will discuss an approach to building and delivering consumable development security services to drive better security.

All-Graphene-Contact Electrically Pumped On-Demand Transferrable Nanowire Source

On-demand NW light sources in a photonic integrated circuit (PIC) have faced several practical challenges. Here, we report on an all-graphene-contact, electrically pumped, on-demand transferrable NW source that is fabricated by implementing an all-graphene-contact approach in combination with a highly accurate microtransfer printing technique. A vertically p-i-n-doped top-down-fabricated semiconductor NW with optical gain structures is electrically pumped through the patterned multilayered graphene contacts. Electroluminescence (EL) spectroscopy results reveal that the electrically driven NW device exhibits strong EL emission between the contacts and displays waveguiding properties. Further, a single NW device is precisely integrated into an existing photonic waveguide to perform light coupling and waveguiding experiments. Three-dimensional numerical simulation results show a good agreement with experimental observations. We believe that our all-graphene-contact approach is readily applicable to various micro/nanostructures and devices, which facilitates stable electrical operation and thus extends their practical applicability in compact integrated circuits.

Rapid curing prospects of geopolymer cementitious composite using frontal polymerization of methyl methacrylate monomer

This paper investigates the prospects of thermal frontal polymerization (FP) technique for rapid curing of fly ash-based geopolymer composite (GPC). In this research, FP is used as an on-demand heat source alternative to conventional external heat application method. This method involves the mixing of an organic monomer (methyl methacrylate - MMA), crosslinker (trimethylolpropane triacrylate – TMPTA), and organic soluble initiator (Aliquat® persulfate - AQPS) with the GPC mortar (fly ash, sodium silicate, sodium hydroxide, and sand) for geopolymerization. An instantaneous application of spot heat initiates the exothermic polymerization of the organic monomer (MMA), forming a reaction front that provides heat needed for the geopolymerization activity, which ultimately produces a solid finished product by propagating through the GPC matrix. This solid finished product is termed in this article as frontally polymerized GPC (FPGPC). The polymerization of the above-mentioned organic monomer (MMA) in the FPGPC matrix was established by FTIR and Raman Spectroscopy. In addition, SEM analysis revealed a hybrid composite consisting of an interpenetrating network (IPN) of inorganic and organic components. This initial study showed that FPGPC achieved impressive compressive strength at early age (within an hour) as compared to both GPC and Ordinary Portland Cement (OPC) companion specimens. However, the strength at latter days and porosity of FPGPC did not match with that of GPC and OPC, which could be improved by optimizing the FPGPC mix and controlling the temperature rise during MMA polymerization. Hence, significant potential of FPGPC as construction material is apparent with limitations to be resolved through further research.

Quantum efficiency, purity and stability of a tunable, narrowband microwave single-photon source

We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.

Multi-sensing paradigm based urban air quality monitoring and hazardous gas source analyzing: a review

Effectively monitoring urban air quality, and analyzing the source terms of the main atmospheric pollutants is important for public authorities to take air quality management actions. Previous works, such as long-term observations by monitoring stations, cannot provide customized data services and in-time emergency response under urgent situations (gas leakage incidents). Therefore, we first review the up-to-date approaches (often machine learning and optimization methods) with respect to urban air quality monitoring and hazardous gas source analysis. To bridge the gap between present solutions and practical requirements, we design a conceptual framework, namely MAsmed (Multi-Agents for sensing, monitoring, estimating and determining), to provide fine-grained concentration maps, customized data services, and on-demand emergency management. In this framework, we leverage the hybrid design of wireless sensor networks (WSNs) and mobile crowdsensing (MCS) to sense urban air quality and relevant data (e.g. traffic data, meteorological data, etc.); Using the sensed data, we can create a fine-grained air quality map for the authorities and relevant stakeholders, and provide on-demand source term estimation and source searching methods to estimate, seek, and determine the sources, thereby aiding decision-makers in emergency response (e.g. for evacuation). In this paper, we also identify several potential opportunities for future research.

Heralded Nondestructive Quantum Entangling Gate with Single-Photon Sources

Heralded entangling quantum gates are an essential element for the implementation of large-scale optical quantum computation. Yet, the experimental demonstration of genuine heralded entangling gates with free-flying output photons in linear optical system, was hindered by the intrinsically probabilistic source and double-pair emission in parametric down-conversion. Here, by using an on-demand single-photon source based on a semiconductor quantum dot embedded in a micropillar cavity, we demonstrate a heralded controlled-NOT (CNOT) operation between two single photons for the first time. To characterize the performance of the CNOT gate, we estimate its average quantum gate fidelity of (87.8±1.2)%. As an application, we generated event-ready Bell states with a fidelity of (83.4±2.4)%. Our results are an important step towards the development of photon-photon quantum logic gates.

Maximally entangled and gigahertz-clocked on-demand photon pair source

We present a 1 GHz-clocked, maximally entangled and on-demand photon pair source based on droplet etched GaAs quantum dots using two-photon excitation. By employing these GaP microlensenhanced devices in conjunction with their substantial brightness, raw entanglement fidelities of up to $0.95 \pm 0.01$ and post-selected photon indistinguishabilities of up to $0.93 \pm 0.01$, the suitability for quantum repeater based long range quantum entanglement distribution schemes is shown. Comprehensive investigations of a complete set of polarization selective two-photon correlations as well as time resolved Hong-Ou-Mandel interferences facilitate innovative methods that determine quantities such as photon extraction and excitation efficiencies as well as pure dephasing directly - opposed to commonly employed indirect techniques.

Mitigation of laser-induced contamination in vacuum in high-repetition-rate high-peak-power laser systems.

Vacuum chambers are frequently used in high-energy, high-peak-power laser systems to prevent deleterious nonlinear effects, which can result from propagation in air. In the vacuum sections of the Allegra laser system at ELI-Beamlines, we observed degradation of several optical elements due to laser-induced contamination (LIC). This contamination is present on surfaces with laser intensity above 30GW/cm2 with wavelengths of 515, 800, and 1030 nm. It can lead to undesired absorption on diffraction gratings, mirrors, and crystals and ultimately to degradation of the laser beam profile. Because the Allegra laser is intended to be a high-uptime source for users, such progressive degradation is unacceptable for operation. Here, we evaluate three methods of removing LIC from optics in vacuum. One of them, the radio-frequency-generated plasma cleaning, appears to be a suitable solution from the perspective of operating a reliable, on-demand source for users.

Etching process of narrow wire and application to tunable-barrier electron pump.

Single electron sources have been studied as a device to establish an electric current standard for 30 years and recently as an on-demand coherent source for fermion quantum optics. In order to construct the single electron source on a GaAs/AlGaAs two-dimensional electron gas (2DEG), it is often necessary to fabricate a sub-micrometer wire by etching. We have established techniques to fabricate the wire made of the fragile 2DEG by combining photolithography and electron beam lithography with one-step photoresist coating, which enables us to etch fine and coarse structures simultaneously. It has been demonstrated that the fabricated single electron source pumps a fixed number of electrons per cycle with radio frequency. The fabrication technique improves the lithography process with lower risk of damage to the 2DEG.