Narrow Results

First direct measurements of the weak decay constant $f_{D_s}(f_D)$ and the $D_s(D)$ branching fractions to $\mu {\nu }_{\mu }$, $\varphi \pi$, $eX$, $\varphi X(\mu {\nu }_{\mu })$ at the BES experiments in 1990s are reviewed. Referring to the BESIII results of $f_{D_s}$ and branching fraction $\mathrm{\text{Br}}(D_s\to \mu {\nu }_{\mu })$ with best precision¹ to date, prospect for challenge on precision measurements of $f_{D_s}$ and $\mathrm{\text{Br}}(D_s\to \mu {\nu }_{\mu })$ at BESIII is presented.

Entanglement is an important resource for quantum technologies that allow us to go beyond the classical world. Quantum systems can be entangled in various ways. Also, the degree of entanglement between the subsystems of a quantum system can be calculated in different ways. In our recent paper [Prog. Theor. Exp. Phys. (2022)], we directly measure the three-tangle of a pure three-qubit quantum state. In this paper, we extend this method to pure N-qubit quantum states (N is any odd number greater than 1) by considering polynomial invariant of degree 4 as a measure of entanglement. In this algorithm, we use quantum gates and output probabilities to calculate polynomial invariant of degree 4. The importance of this method lies in the possibility of experimental implementation of quantum calculations in the language of quantum gates.

The electrocaloric effect (ECE) in lead-free BaSn_xTi${}_{1-x}$O₃ (BSnT, $x=0.05$, 0.10 and 0.15) ceramics were investigated using a direct ECE measurement. Results indicate that the maximum ECE occurs near the Curie temperature and it slightly shifts towards high temperatures. The directly measured ECE is larger than that calculated using the Maxwell relation and P-E loops. A maximum electrocaloric efficiency $\mathrm{\Delta }T∕\mathrm{\Delta }E=0.49\times 10^{-6}$KmV${}^{-1}$ was procured for the composition with $x=0.15$ at $T=299.2$K. And it also shows a broad peak in the temperature range of 250–320K.

Purely leptonic decays of the D_s(D) meson in the reaction $e^{+}{e}^{-}\to D_s^{+}{D}_s^{-}\left(D^{*+}{D}^{-}\right)$ are observed by the BES group at the BEPC collider. Direct measurements of the weak decay constant f_Ds (f_D) and the D_s(D) branching fractions to μν_μ, ϕπ, eX, ϕX (μν_μ) are obtained for the first time.

The photon helicity may be mapped to a spin-1/2, whereby we put forward an effective interaction (a scalar) between a light beam and an electron spin current through virtual optical transitions in a direct-gap semiconductor such as GaAs. Such an effective interaction is possible since the pure spin current and the photon spin current, both keeping the time-reversal symmetry but breaking the space-inversion symmetry of the system, are of the same tensor type, namely, the rank-2 pseudo-tensor. The optical effects due to the effective coupling induces the circular birefringence, which is similar to the Faraday rotation in magneto-optics but nevertheless involve no net magnetization. Such optical birefringence effect of a pure spin current originate from the intrinsic spin-orbit coupling in valence bands but involves neither the Rashba effect from structure inversion asymmetry nor the Dresselhaus effect due to bulk inversion asymmetry of the material. This novel optical birefringence effect may be exploited for direct, non-demolition measurement of a pure spin current.