The recently proposed twin-field quantum key distribution (TF-QKD) effectively overcomes the key capacity limitation without quantum relay and achieves long-distance quantum key distribution. In this ...paper, based on the TF-QKD protocol by Lucamarini et al. M. Lucamarini, Z.L. Yuan, J.F. Dynes, A.J. Shields, Nature
557
, 400 (2018), we propose a scheme where the weak coherent state (WCS) is replaced by a heralded single photon source (HSPS), and compare their performance by calculating the key rate. The numerical simulation results show that TF-QKD using HSPS can still break through the rate-distance limitation. Specifically, compared with the WCS TF-QKD protocol, the HSPS TF-QKD protocol has a lower secret key rate but a greater distance. Thus we show the TF-QKD with HSPS is a more preferable protocol for long distance transmittance.
Graphical abstract
The propensity of Zn‐metal anodes to form non‐uniform or dendritic electrodeposits is bound up with the nature of the electrode surface. However, the effect of surface structure on the inherent ...nucleation and deposition of Zn is not yet well understood. Here, the surface structure of a Zn‐metal anode is reconstructed with Sn‐crystal textures via a facile chemical displacement reaction. Compared to the bare Zn, the high‐affinity Zn binding sites of Sn afford lower deposition energy barrier, which promotes deposition kinetics. What is more, a Sn‐textured surface with moderate Zn affinity but high average surface energy ensures a better wettability from the deposits, leading to the lateral growth of Zn crystals. The resultant Sn‐textured Zn‐metal anode exhibits an extremely low voltage hysteresis of 20 mV and achieves a prolonged cycling stability over 500 h cycles without dendrite formation. This work provides new insights into the crystal‐texture‐dependent Zn electrodeposition process and offers direction for direct surface texturing to better stabilize Zn‐metal anodes with improved reversibility.
The surface of a Zn‐metal anode is reconstructed with Sn‐crystal textures via a facile chemical displacement reaction. Such a Sn‐textured surface not only endows a reduced Zn deposition energy barrier but also regulates the lateral growth of Zn crystals, which promotes dendrite‐free electrodeposits and leads to the achievement of an extremely low voltage hysteresis of 20 mV and prolonged cycling performance over 500 h.
SpinQ Gemini is a commercial desktop quantum computing platform designed and manufactured by SpinQ Technology. It is an integrated hardware-software system. The first generation product with two ...qubits was launched in January 2020. The hardware is based on NMR spectrometer, with permanent magnets providing ∼1 T magnetic field. SpinQ Gemini operates under room temperature (0–30°C), highlighting its lightweight (55 kg with a volume of
70
×
40
×
80
cm
3
), cost-effective (under 50k USD), and maintenance-free. SpinQ Gemini aims to provide real-device experience for quantum computing education for K-12 and at the college level. It also features quantum control design capabilities that benefit the researchers studying quantum control and quantum noise. Since its first launch, SpinQ Gemini has been shipped to institutions in Canada, Taiwan and Mainland China. This paper introduces the system of design of SpinQ Gemini, from hardware to software. We also demonstrate examples for performing quantum computing tasks on SpinQ Gemini, including one task for a variational quantum eigensolver of a two-qubit Heisenberg model. The next generations of SpinQ quantum computing devices will adopt models of more qubits, advanced control functions for researchers with comparable cost, as well as simplified models for much lower cost (under 5k USD) for K-12 education. We believe that low-cost portable quantum computing products will facilitate hands-on experience for teaching quantum computing at all levels, well-prepare younger generations of students and researchers for the future of quantum technologies.
High quality stoichiometric EuO ferromagnetic thin films have been grown by Molecular Beam Epitaxy (MBE) on MgO coated-Yttria Stabilized Zirconia (YSZ) (100) substrates. The proof is made that ...introducing an MgO buffer layer, that avoid oxygen transfer from YSZ to EuO, allows the preparation of high quality stoichiometric EuO films at reduced deposition temperature compared with films directly deposited onto YSZ, maintaining similar Eu flux and oxygen partial pressure. Structure and texture were characterized by X-ray diffraction showing out-of plane and in-plane ordering for films deposited onto MgO buffer layers. The crystallographic quality was corroborated by a Curie temperature around 69K and a magnetization moment close or equal to 6.49·10−23J/T (7 μB), corresponding to bulk EuO single crystal values.
► EuO films were epitaxially grown on MgO coated Yttria Stabilized Zirconia. ► Deposition temperature was reduced compared to bare Yttria Stabilized Zirconia. ► Epitaxial texture was confirmed by in-plane X-ray diffraction. ► Composition of the heterostructure was defined by X-ray Photoelectron Spectroscopy. ► Single crystal like EuO magnetic moment and coercive field were measured.
•The ferromagnetism and conductivity in LaMnO3 are greatly enhanced after oxygen-atmosphere annealing.•The trivalent Mn ions become trivalent and tetravalent mixed in the annealed film.•Jahn-Teller ...interaction is suppressed due to a reduction of MnO6 distortion.
We have investigated the effect of the excess oxygen on the structural, magnetic, and transport properties in LaMnO3 thin films by post-annealing in the oxygen atmosphere. The ferromagnetism and conductivity of the LaMnO3 films are greatly enhanced after post-annealing. The valence states of Mn ions are trivalent in the as-grown film and become trivalent and tetravalent mixed in the annealed film. Jahn-Teller interaction is suppressed due to a reduction of MnO6 distortion, confirmed by Raman spectra. The conversion from Mn3+ to Mn4+ and suppression of the Jahn-Teller interaction are responsible for the enhancement of ferromagnetism and conductivity in annealed films.
Magnetic nanoparticles were created in or around the sulfonated (s) polystyrene domains in a phase separated polystyrene-
b-(ethylene-
co-butylene)-
b-styrene) block copolymer (BCP) using an in situ ...inorganic precipitation procedure. The sBCP was neutralized with a mixed iron/cobalt chloride electrolyte and the doped samples were converted to their oxides by reaction with sodium hydroxide and further washing with water. Transmission electron microscopy indicated the presence of nanoparticles in the 5–25
nm size range. The metal oxide particle structures were studied using select area electron diffraction, which revealed that they are of the cobalt iron oxide composition (CoFe
2O
4). These nanocomposites were shown, using a superconducting quantum interference device magnetometer, to be superparamagnetic at 300
K and ferrimagnetic at 5
K. Nanocomposites consisting of smaller particles have a blocking temperature of 70
K, whereas it was 140
K for larger particles.
Fully epitaxial FeCo/MgO/Fe magnetic tunnel junctions on silicon substrates were fabricated using in situ shadow-masks in an electron-beam deposition system. An inverse tunneling magnetoresistance ...(TMR) of −39% was observed at 77 K after annealing, which was not obtained in MTJs grown in better vacuum with the same device structure. This inverse TMR is attributed to the oxidation of the FeCo/MgO interface, which provides a negative spin polarization. Our work highlights the importance of interfacial properties on tunneling magnetoresistance and points to a simple processing route to achieve inverse TMR by carefully controlling the oxidation condition of the bottom layer.
Display omitted
•A simple method was proposed to achieving inverse TMR by carefully controlling the oxidation condition of the bottom layer.•Fully epitaxial FeCo/MgO/Fe magnetic tunnel junctions patterned by in situ shadow-masks were fabricated.•Inverse tunneling magnetoresistance of −39% was observed.
With the increasing development of localization of space traveling wave tubes (STWT), the reliability of domestic STWT is the most urgent problem at present. Among them, the maintenance of high ...vacuum of the STWT is the most important reason for the reliability of the STWT. The vacuum measurement of the STWT at the process stages of vacuum baking, tuning and burn-in, and baseplate soldering is of great significance for the reliability improvement of the STWT. In this paper, a high-vacuum ionization gauge is installed in the STWT to realize the measurement of the vacuum inside the traveling wave tube at different process stages. The results show that: after baking and exhaust, the extreme vacuum of the collector is an order of magnitude different from that of the main pipe; at the process of tuning and burn-in. The vacuum will be about 5 times worse under different working conditions of the STWT. The vacuum of the STWT will be doubled during the soldering process of the baseplate. The conclusion of this paper can provide a detection method for the ultra-high vacuum of the STWT, and provide a basis for the improvement of the reliability of the STWT.
This paper describes the on-orbit performance of downlink amplifiers (L-band TWTA) for Beidou Navigation Satellites. The integrator of TWTA is CAST Xi' an, and the suppliers of TWT include AIRCAS, ...BVERI,and NanJing SanLe Group Co. Ltd. It Is very interesting to compare the variation of the helix current and anode voltage, and it is useful to predict the range of the helix current and anode voltage during the orbital life(ten to twelve years).
High-frequency parameter determines the output power and gain characteristics of a traveling wave tube. The relationship between the harmonics and the fundamental parameters determines the harmonic ...and fundamental proportion of the output power. Within a relatively broad range of parameter variation, the impacts on second harmonic from the distribution of phase velocity and coupling impedance are compared. We conclude that when the phase velocity proportion of harmonic to fundamental wave is approximately 0.96, the harmonic wave reaches its peak value. The higher proportion of coupling impedance is, the greater harmonic is.
PDF
