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In this paper, we present the development of a graphene-based hot electron bolometer with Johnson noise readout. The bolometer is a graphene microbridge connected to a log spiral antenna by Au contact pads. The Fourier transform spectrometer measurement shows the bolometer has high coupling efficiency in the frequency range from 0.3 to 1.6 THz. Using 300/77 K blackbody loads, we measure an optical noise equivalent power of 5.6 × 10 −12  W/Hz 0.5 at 3.0 K. To understand the thermal transport inside the graphene microbridge, we measure the bolometers with different microbridge lengths at different bath temperatures. We find that the thermal conductance due to electron diffusion is significant in the bolometers.

A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism 1 , in which the properties of the physical world are independent of our observation of them and no signal travels faster than light. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings 2 , 3 . Although technology can satisfy the first two of these requirements 4 – 7 , the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human ‘free will’ could be used rigorously to ensure unpredictability in Bell tests 8 . Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology 9 . The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons 5 , 6 , single atoms 7 , atomic ensembles 10 and superconducting devices 11 . Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bipartite and tripartite 12 scenarios. Project outcomes include closing the ‘freedom-of-choice loophole’ (the possibility that the setting choices are influenced by ‘hidden variables’ to correlate with the particle properties 13 ), the utilization of video-game methods 14 for rapid collection of human-generated randomness, and the use of networking techniques for global participation in experimental science. The BIG Bell Test, which used an online video game with 100,000 participants worldwide to provide random bits to 13 quantum physics experiments, contradicts the Einstein–Podolsky–Rosen worldview of local realism.

We have developed four-leg-supported superconducting Ti transition-edge sensors (TES) formed by KOH wet etching. Energy relaxation mechanism is changed from electron–phonon coupling to diffusive phonon after wet etching. The current–voltage curves of the same TES device were measured before and after wet etching. After wet etching, its thermal conductance ( G ) is reduced to 500 pW/K from 8950 pW/K. The measured effective response time ( τ eff ) is 143 μs, about 30 times larger. In addition, we have studied the optical noise equivalent power (NEP) with a cryogenic blackbody in combination with metal-mesh filters to define the radiation bandwidth. The obtained optical NEP is 5 × 10 −16  W/√Hz, which is suitable for ground-based astronomical applications.

Superconducting transition-edge sensors (TESs) are widely used to detect electromagnetic radiation ranging from millimeter wave to γ-ray photons. The energy resolution of TESs is mainly determined by their critical temperature ( T C ). We propose to tune the T C of Ti film by baking in air for a period at a moderate temperature and find that T C is inversely proportional to the logarithm of baking time ( t baking ) for a given baking temperature ( T baking ), but scales with the square of T baking for a given t baking . Ti film covered by a thin Au protection layer follows the same trend when baked in air. Based on the XPS analysis, we attribute the change in T C of Ti films to the oxidation at the surface and diffusion of oxygen into the films. In addition, the aging effect of Ti films is similar to that of baking in air but with much slower change rate.

We report on self-aligned Ti TES single-photon detectors embedded in a 1550 nm optical cavity. The circular TES chip is shaped with a dry-etch process from the backside to protect the TES and wiring from possible damage and aligned to a single-mode fiber using a standard fiber ferrule and a matching sleeve. The critical temperature of Ti film is about 300 mK, resulting in a relatively short time constant of 1.3 μs. By choosing an active area of 15 × 15 μm 2 , our optical Ti TES can distinguish single photons at 1550 nm and reaches a system photon detection efficiency of 55% and an energy resolution of about 0.7 eV.

Hot-electron bolometers (HEBs) based on Johnson noise thermometry are potential terahertz detectors with high sensitivity and wide dynamic range. Understanding the thermal conductance of these detectors is crucial, as their sensitivity scales linearly with this property. In this paper, we focus on the experimental study of the thermal conductance of the titanium HEBs with different microbridge thicknesses ranging from 15 to 59 nm. We find that the thermal conductance of the HEBs takes a temperature power law of T n , and the exponent n decreases from 3.4 to 2.8 as the microbridge thickness increases. The variation of the exponent n is mainly due to electron diffusion, which is not completely suppressed by superconducting contacts and is stronger in thick microbridges. In addition, we observed that the thermal radiation from the low-noise amplifier for Johnson noise readout may raise the electron temperature by about 30 mK at the bath temperature of 0.25 K, giving an excessive thermal conductance.

Superconducting transition-edge sensors (TESs) have demonstrated high detection efficiency and photon-number-resolving capability, making TESs attractive in quantum information and astrophysics. Aiming to achieve high energy detection efficiency (i.e., the ratio of the detected energy to incident energy), we integrate the TES in an optical cavity, consisting of 16-layer dielectric reflection mirror and 4-layer antireflection coating. The critical temperature was decreased to 260 mK after deposition of antireflection coating from its original 323 mK. The energy detection efficiency was increased by a factor of two, up to 40%, thanks to the enhancement of photon absorption by adding the optical cavity.

In the traditional inventory problem, to secure demand risk a retailer often requests the right to return unsold goods, although this is associated with higher wholesale prices. Various studies have attempted to illustrate the returns scenario. However, these studies have focused on optimization from the retailer's perspective only, and have thus ignored the fact that the manufacturer might have no incentive to accept returns. This study takes account of the self-interest of both the retailer and the manufacturer, and demonstrates that a quantity discount scheme should provide the manufacturer with incentive to accept returns. A three-stage theoretical model is developed and presented to illustrate the returns-quantity discounts contract, and demonstrates that the contract is self-enforcing. Furthermore, it is demonstrated that Pareto efficiency can be attained in the model. The scenarios are illustrated through a numerical example.

A hot electron bolometer (HEB) with Johnson noise readout is an attractive technique for radiation detection due to its high sensitivity, wide operating temperature range, and large dynamic range. In this paper, we present the development of a terahertz HEB based on Johnson noise readout. The HEB consists of a titanium microbridge connected to two high-energy-gap niobium contacts for confining hot electrons. We measured the thermal conductance and noise equivalent power (NEP) of the HEB at different bath temperatures. We find that the thermal conductance due to the electron–phonon interaction increases with temperature as T 2.5 . At 3.0 K, the thermal conductance is found to be 37.9 ± 1.4 nW/K and the electrical NEP is as low as 23.0 ± 0.8 pW/ Hz . In addition, we find that the HEB works efficiently up to 15 μW input power.

Though innovation strategy and organizational learning have been credited to impact on product innovation performance, they have been rarely considered in a single model simultaneously. Thus, the main aim of the paper is to investigate the extent of impact of innovation strategy on organizational learning and product innovation performance. A structural equation modelling analysis was performed on the survey data collected from Ethiopian textile and leather product manufacturing firms. The result reveals that innovation strategy is positively related to product innovation performance. Further, firm size and ownership type moderate the effect of innovation strategy on product innovation performance.