Nonlinear improvement of measurement-device-independent quantum key distribution using multimode quantum memory

This paper proposes a quantum key distribution (QKD) scheme for measurement-device-independent QKD (MDI-QKD) utilizing quantum memory (QM), which is based on two distinct functions of QM: on-demand storage and multimode storage. We demonstrate a nonlinear increase in the secure key rate due to the utilization of QM. In the protocol incorporating on-demand storage, it is acknowledged that the secure key rate is scaled by $R=O(\sqrt{\eta_{ch}})$ as $\eta_{ch}$, while as an alternative approach, we reveal that the improvement is $O(m_s^2)$, with $m_s$ being the number of modes in frequency (spatial) multiplexing in the scheme incorporating multimode storage. We adopt an atomic frequency comb as a QM that incorporates the two functions and propose an architecture based on MDI-QKD to attain experimental feasibility. This scheme can be extended to quantum repeaters, and even for a single quantum-repeater node, there is a nonlinear enhancement and an experimental incentive to increase the number of modes.Comment: 18 pages, 9 figure

Overconfidence Increases Productivity

Recent studies report that productivity increases under tournament reward structures than under piece rate reward structures. We conduct maze-solving experiments under both reward structures and reveal that overconfidence is a significant factor in increasing productivity. Specifically, subjects exhibiting progressively higher degrees of overconfidence solve more mazes. This result shows a positive aspect of overconfidence, which usually has been examined in its negative aspect as an expectation bias.

Estimation of Social Costs of Highways in Japan

The main purpose of this paper is to estimate and evaluate the social costs of highways in Japan. In general, with more people concerned about protecting the environment at both local and global levels, dependence on vehicular transportation in cities has brought about problems. Too much dependence on autos causes air pollution, which has detrimental health effects. Furthermore, traffic congestion wastes time, money, and energy. The most concerning issue related to continuing dependence on car use is global warming. In order to implement transport policies conducive to creating a sustainable environment, it is necessary to measure correctly the social costs of vehicular transport such as traffic accidents, air pollution, noise, global warming, and traffic congestion. By using a data set from Japan, this paper aims to estimate the social costs of vehicular transport on highways and to evaluate how extensive these social costs are by comparing, for example, highway fares relative to GDP. Our study has several distinguishing characteristics. The most important point is that we estimate each individual highwayfs social costs by considering average speed at the peak period, total traffic volume, types of vehicular transport and so on. Second, this study distinguishes five kinds of social costs of vehicular transport for individual highways in Japan: 1) traffic accidents, 2) air pollution, 3) noise, 4) global warming, and 5) traffic congestion. Third, by using a data set of over 50 individual highways in Japan in 2005, we analyze the relationship between the social costs of vehicular transport and traffic volumes in general. Last, by comparing highway fares, the degree of GDP, the fuel tax level, and other factors, we assess the magnitude of social costs, for the purpose of creating prudent transport policy. In order to attain the objectives mentioned above, we organize our study as follows. First, we summarize previous studies, with special attention to the kinds of social costs used, the kinds of sub-items considered in estimating social costs, the aggregate level, the method of estimation, and the magnitude of the social costs of vehicular transport. Second, we explain our method for estimating social costs. In this section, we describe specific equations for the five main categories of highwaysf social costs. Third, based on these equations, by using a data set for highways in Japan, we estimate the social costs of vehicular transport on highways. Last, by comparing highway fares, and GDP and so on, we evaluate how extensive highwaysf social costs actually are. In this section, we also summarize our major findings

Overconfidence increases productivity

Recent studies report that productivity increases under tournament reward structures than under piece rate reward structures. We conduct maze-solving experiments under both reward structures and reveal that overconfidence is a significant factor in increasing productivity. Specifically, subjects exhibiting progressively higher degrees of overconfidence solve more mazes. This result shows a positive aspect of overconfidence, which usually has been examined in its negative aspect as an expectation bias

Older sisters and younger brothers: The impact of siblings on preference for competition

Studies in psychology have long argued the possibility that sibling structure, such as birth order and the gender of siblings, shapes one's feminine and masculine personality traits, such as a preference for competition. In light of recent developments in the economics literature on the gender gap, this implies that familial environment could explain why some women do opt for competition, while the vast majority of women do not and, thus, are underrepresented on the career ladder. By conducting a controlled experiment on Japanese high school students, this study quantifies the impact of sibling structure on one's preference for competition, and examines whether a long-debated sibling hypothesis in psychology is supported from the viewpoint of experimental economics. Consistent with the hypothesis, our results reveal that men with older sisters were significantly less likely to enter a competitive environment compared with only sons. This effect is comparable in size to the effect of being female on the decision to compete. Our study also found moderate evidence that women with younger brothers were more likely to compete than only daughters

Multicascade-linked synthetic wavelength digital holography using an optical-comb-referenced frequency synthesizer

Digital holography (DH) is a promising method for non-contact surface topography because the reconstructed phase image can visualize the nanometer unevenness in a sample. However, the axial range of this method is limited to the range of the optical wavelength due to the phase wrapping ambiguity. Although the use of two different wavelengths of light and the resulting synthetic wavelength, i.e., synthetic wavelength DH, can expand the axial range up to a few tens of microns, this method is still insufficient for practical applications. In this article, a tunable external cavity laser diode phase-locked to an optical frequency comb, namely, an optical-comb-referenced frequency synthesizer, is effectively used for multiple synthetic wavelengths within the range of 32 um to 1.20 m. A multiple cascade link of the phase images among an optical wavelength (= 1.520 um) and 5 different synthetic wavelengths (= 32.39 um, 99.98 um, 400.0 um, 1003 um, and 4021 um) enables the shape measurement of a reflective millimeter-sized stepped surface with the axial resolution of 34 nm. The axial dynamic range, defined as the ratio of the maximum axial range (= 0.60 m) to the axial resolution (= 34 nm), achieves 1.7*10^8, which is much larger than that of previous synthetic wavelength DH. Such a wide axial dynamic range capability will further expand the application field of DH for large objects with meter dimensions.Comment: 19 pages, 7 figure