Phys.org April 26, 2021 Microwave-based satellite–ground links cannot fully satisfy the requirements of metrology, navigation, positioning, and very long baseline interferometers. Researchers in China investigated the possibility of an optical-based satellite–ground link, where the transferred carriers are pulsed lasers, resulting in a link with a high time resolution and a large ambiguous range. They analyzed the parameters of satellites in different orbits and concluded that high-orbit links enable more stable time–frequency comparison or dissemination by taking advantage of the long duration, a large common view range, and the lower relativistic effects. They performed a 16 km free-space transfer experiment to […]
Tag Archives: S&T China
Scientists achieve single-photon imaging over 200 kilometers
Phys.org April 5, 2021 The operating range of practical single photon lidar systems is limited to about tens of kilometers over the Earth’s atmosphere, mainly due to the weak echo signal mixed with high background noise. By using high-efficiency optical devices for collection and detection, and new noise-suppression technique that is efficient for long-range applications researchers in China have developed a compact coaxial single-photon lidar system capable of realizing 3D imaging at up to 201.5 km. They developed photon-efficient computational algorithms which enabled accurate imaging with as few as 0.44 signal photons per pixel. The research is a significant step […]
Spin-to-charge conversion achieves 95% overall qubit readout fidelity
EurekAlert April 1, 2021 The current single-shot readout of the nitrogen-vacancy electron spin relies on resonance fluorescence method at cryogenic temperature. However, the spin-flip process interrupts the optical cycling transition, therefore, limits the readout fidelity. Researchers in China have introduced a spin-to-charge conversion method assisted by near-infrared light to suppress the spin-flip error which leverages high spin-selectivity of cryogenic resonance excitation and flexibility of photoionization. They achieved an overall fidelity > 95% for the single-shot readout of an NV center electron spin in the presence of high strain and fast spin-flip process. With further improvements, this technique has the potential to achieve […]
Scientists propose novel self-modulation scheme in seeded free-electron lasers
Phys.org March 11, 2021 Seeded free-electron lasers (FELs), which use the frequency up-conversion of an external seed laser to improve temporal coherence, are ideal for providing fully coherent soft x-ray pulses. However, it is difficult to operate seeded FELs at a high repetition rate due to the limitations of present state-of-the-art laser systems. Researchers in China have developed self-modulation method for enhancing laser-induced energy modulation, thereby significantly reducing the requirement of an external laser system. They have experimentally realized high harmonic generation in a seeded FEL using an unprecedentedly small external laser-induced energy modulation. The results pave a way for […]
An intelligent soft material that curls under pressure or expands when stretched
Nanowerk February 24, 2021 Existing perceptive soft actuators require complex integration and coupling between the discrete functional units to achieve autonomy and intelligently interact with humans and the environment. Researchers in China have developed actuators with embodied sensing, actuation, and control at the single-unit level by synergistically harnessing the mechanosensing and electrothermal properties of liquid metal (LM) to actuate the thermally responsive liquid crystal elastomer (LCE). They created multifunctional LM circuits on the LCE surface using a simple and facile methodology based on magnetic printing. The fluidic LM circuit can be utilized as a conformable resistive heater, and a sensory […]
Long-distance and secure quantum key distribution (QKD) over a free-space channel
Phys.org January 25, 2021 Measurement-device-independent quantum key distribution (MDI-QKD) protocol can help in closing all loopholes on detection at once. It has only been successfully implemented using fiber optics. To implement the protocol across free-space channels two main challenges need to be addressed. One is to reduce the gap between theory and practice of QKD, and the other one is to extend the distance of QKD. Researchers in China have developed a robust adaptive optics system – high-precision time synchronization and frequency locking between independent photon sources located far apart to realize free-space MDI-QKD over a 19.2-km urban atmospheric channel. […]
Using drones to create local quantum networks
Phys.org January 18, 2021 Researchers in China built a small laser-generating device and affixed it to one of the drones. As it fired, photons were split in two, creating entangled pairs. One of the paired photons was directed toward another drone while the other was directed to a ground station. The drone that received the entangled photon served only as a relay—after refocusing, the photon was forwarded to a third drone, which then sent it to a second ground station. Motorized devices were used on the drones to ensure transmitters and received lined up properly for transmission of the entangled […]
Researchers fabricate co-doped aluminosilicate fiber with high laser stability for multi-kW level laser
Phys.org November 27, 2020 Fiber fabrication technology have led to an exponential increase in the output power of CW fiber lasers. However, with further scaling the output power, photodarkening (PD) is the critical limit factor for long-term laser reliability under multi kW level output power. Researchers in China demonstrated stable performance in fiber fabricated the Yb/Ce codoped aluminosilicate laser. The molar ratio of Ce/Yb was designed and optimized to be 0.58 for low background loss, effective photodarkening suppression, and no additional thermal load. The background loss of was 4.7 dB/km and its photodarkening loss at equilibrium was as low as 3.9 […]
Researchers invent broad-band tunable terahertz absorber
Phys.org November 24, 2020 THz absorbers with strong absorption, broad-band absorption bandwidth and tunable characteristics have attracted the attention of many researchers with extensive application prospects in THz wave shielding, THz imaging, and THz sensitive thermal detecting. Researchers in China introduced strongly correlated electron material VO2 as a functional layer and realized the broad-band tunable THz spectrum properties in the device. The conductivity, dielectric constant, as well as optical properties got a dramatic switching during the insulator-metal transition at TC = 340 K, and the transition could be tuned by temperature, electric field, and light. The device had a 74% […]
Single-atom alloy: Superb cocatalyst for photocatalysis
Phys.org October 28, 2020 While surface charge state of co-catalysts plays a critical role for boosting photocatalysis, the study on surface charge regulation via their precise structure control, remains rare. Researchers in China have fabricated an MOF-stabilized bimetallic Pd-Pt nanoparticles which feature adjustable Pt coordination environment and the controlled structure from core-shell to single-atom alloy (SAA). They found that Pt surface charge regulation can be alternatively achieved by changing its coordination environment and the structure of Pd-Pt co-catalyst, where the charge between Pd and Pt is redistributed. The optimized Pd-Pt composite exhibits an exceptionally high photocatalytic hydrogen production activity, far […]