Feedback control of quantum entanglement in a two-spin system

A pair of spins is the most simple quantum system that can possess entanglement, a non-classical property playing an essential role in quantum information technologies. In this paper, feedback control problems of the two-spin system conditioned on a continuous measurement are considered. In order to make some useful formulas in stochastic control theory directly applicable, we first derive a two-dimensional description of the system. We then prove that a feedback controller stabilizes an entangled state of the two spins almost globally with probability one. Furthermore, it is shown that another entangled state, which corresponds to a non-equilibrium point of the dynamics, is stabilized via feedback in the sense that the expectation of the distance from the target can be made arbitrarily small

Perfect difference systems of sets and Jacobi sums

AbstractA perfect (v,{ki∣1≤i≤s},ρ) difference system of sets (DSS) is a collection of s disjoint ki-subsets Di, 1≤i≤s, of any finite abelian group G of order v such that every non-identity element of G appears exactly ρ times in the multiset {a−b∣a∈Di,b∈Dj,1≤i≠j≤s}. In this paper, we give a necessary and sufficient condition in terms of Jacobi sums for a collection {Di∣1≤i≤s} defined in a finite field Fq of order q=ef+1 to be a perfect (q,{ki∣1≤i≤s},ρ)-DSS, where each Di is a union of cyclotomic cosets of index e (and the zero 0∈Fq). Also, we give numerical results for the cases e=2,3, and 4

Measuring the quality of life of long-term care service users in Japan: a cross-sectional questionnaire study

[Background] In Japan’s super-aging society, the number of long-term care service providers is increasing, and the quality of care is a matter of concern. One aspect of the quality of care is the user’s quality of life. The questionnaires EQ-5D and WHO-5 are representative indicators of quality of life. Herein, we aimed to measure the quality of life in long-term care service users in Japan and to clarify the relationship between quality of life and the level of care required. [Methods] A questionnaire study was conducted in 106 facilities of 22 corporations. In addition to the EQ-5D and WHO-5, sex, age, and the level of care required were assessed by descriptive statistics. Bonferroni’s multiple comparison test was used to analyze each quality of life score, and the differences by sex and age were analyzed multiple regression analyses, with each quality of life score as the objective variable. [Results] Of 4647 cases collected, 2830 were analyzed, with no missing data. Both indicators tended to be lower than the general older population. Those scores tended to be higher in females than males (EQ-5D: males, 0.58 ± 0.26; females, 0.60 ± 0.24; P = 0.06 and WHO-5: males, 13.8 ± 5.92; females 14.9 ± 5.70; P < 0.001). In terms of age, those under 65 years old with specific diseases had lower EQ-5D scores than those in other age groups (P < 0.001); however, WHO-5 scores did not differ by age. Multiple regression analysis showed a significant association between the EQ-5D score and level of care required, except for support-required level 1, which tended to worsen as the level of care required increased. Conversely, the WHO-5 score was significantly lower for care need levels 2, 4, and 5. [Conclusions] The quality of life of long-term care service users was worse than that of the general older population, it tended to be low among males and those under 65 years old with specific diseases. Furthermore, it gradually decreased as the level of care required increased. It is important to monitor users’ quality of life as a quality indicator of care, to improve and manage it

Suboptimal quantum-error-correcting procedure based on semidefinite programming

In this paper, we consider a simplified error-correcting problem: for a fixed encoding process, to find a cascade connected quantum channel such that the worst fidelity between the input and the output becomes maximum. With the use of the one-to-one parametrization of quantum channels, a procedure finding a suboptimal error-correcting channel based on a semidefinite programming is proposed. The effectiveness of our method is verified by an example of the bit-flip channel decoding.Comment: 6 pages, no figure, Some notations differ from those in the PRA versio

Who Realizes a PSS?: An Organizational Framework for PSS Development

AbstractIn manufacturing, Product-Service Systems (PSS) that create value by coupling a physical product and a service have been attracting attention. According to this background, many researchers have proposed PSS development methods that provide guidance on HOW TO realize a PSS. However, difficulties still remain with regard to constructing an organization for PSS development; i.e., answering the question, WHO realizes a PSS? In order to clarify problems with regard to constructing the organization, this paper proposes an organizational framework for PSS development. Based on this framework, this paper points outsome research challenges with regard to constructing the organization for PSS development, and then, introducing the PSS development methods that can address these challenges

Optimization of capacitive coupled Low Gain Avalanche Diode (AC-LGAD) sensors for precise time and spatial resolution

Capacitive-coupled Low-Gain Avalanche Diode (AC-LGAD) sensors are being developed for high-energy particle physics experiments as a detector which provides fast time information with fine spatial resolution. This paper describes optimizations of AC-LGAD sensor fabrication parameters, such as doping concentrations of the gain and electrode layers as well as the AC insulator capacitance, to realize $\mathcal{O}$(10)~\um{} spacial resolution, small charge cross talk to the neighboring electrodes, detection efficiency higher than 99\% at a 10$^{-4}$ fake rate and time resolution of about 30~ps. The radiation tolerance of the sensor is presented. In addition, further application to a device capable of visible and infra-red light detection is discussed.Comment: 11 pages, 25 figures, Submitted to Nuclear Instruments & Methods in physics research A (NIMA