Turbo码MPSK调制系统的简化比特度量算法研究

研究了一种适用于Turbo码MPSK调制系统的简化比特度量计算方法,并对其修正使之能应用于Turbo码的Log-Map译码算法,在AWGN信道中对采用修正算法的Turbo码8PSK调制系统进行了性能仿真。结果表明,该算法性能逼近最大似然比特度量算法,同时计算复杂度大大降低。

Application of Y(sl(2)) Algebra for Entanglement of Two-Qubit System

We construct the transition operators in terms of the generators of the general Yangian and the reduced Yangian. By acting these operators on a two-qubit pure state, we find that the entanglement degrees of the states are all decreased from the certain values to zero for the reduced Yangian algebra, which makes the state disentangled. This result sheds new light on the physical meaning of Y （sl（2） ） in quantum information.

Experimental study of fatigue degree quantification for multi-feature fusion identification

A comprehensive quantification method of fatigue degree is proposed concerning subjective and objective quantifications.Using the fatigue degree test software,fatigue degree is objectively quantified by analyzing the reaction and operation abilities of drivers about traffic signals.By comparison experiment with that EEG signal based,multivariate statistical analysis and fusion identification based on BP neural network(BPNN) results show that the experimental procedure is simple and practical,and the proposed method can reveal the correlation between fatigue feature parameters and fatigue degree in theory,and also can achieve accurate and reliable quantification of fatigue degree,especially under the associated action of multiple fatigue feature parameters.

Symmetry Analysis of Barotropic Potential Vorticity Equation

Recently F. Huang [Commun. Theor. Phys. 42 （2004） 903] and X. Tang and P.K. Shukla [Commun. Theor. Phys. 49 （2008） 229] investigated symmetry properties of the barotropic potential vorticity equation without forcing and dissipation on the beta-plane. This equation is governed by two dimensionless parameters, F and β, representing the ratio of the characteristic length scale to the Rossby radius of deformation and the variation of earth＇ angular rotation, respectively. In the present paper it is shown that in the case F ≠ 0 there exists a well-defined point transformation to set β = 0. The classification of one- and two-dimensional Lie subalgebras of the Lie symmetry algebra of the potential vorticity equation is given for the parameter combination F ≠ 0 and β = 0. Based upon this classification, distinct classes of group-invariant solutions are obtained and extended to the case β ≠0.

Quantum computational advantage via 60-qubit 24-cycle random circuit sampling

To ensure a long-term quantum computational advantage,the quantum hardware should be upgraded to withstand the competition of continuously improved classical algorithms and hardwares.Here,we demonstrate a superconducting quantum computing systems Zuchongzhi 2.1,which has 66 qubits in a two-dimensional array in a tunable coupler architecture.The readout fidelity of Zuchongzhi 2.1 is considerably improved to an average of 97.74%.The more powerful quantum processor enables us to achieve larger-scale random quantum circuit sampling,with a system scale of up to 60 qubits and 24 cycles,and fidelity of FXEB=(3·66±0·345)×10^(-4).The achieved sampling task is about 6 orders of magnitude more difficult than that of Sycamore[Nature 574,505(2019)]in the classic simulation,and 3 orders of magnitude more difficult than the sampling task on Zuchongzhi 2.0[arXiv:2106.14734(2021)].The time consumption of classically simulating random circuit sampling experiment using state-of-the-art classical algorithm and supercomputer is extended to tens of thousands of years(about 4·8×104years),while Zuchongzhi 2.1 only takes about 4.2 h,thereby significantly enhancing the quantum computational advantage.

Non-zero quantum discord at finite temperature

We investigate theoretically the quantum discord dynamics of a two-qubit composite system subject to a common finite-temperature reservoir by solving the Born-Markovian master equation analytically.The ultimate quantum discord,however,exhibits a relatively high stable value associated with the reservoir temperature despite the permanent disappearance of entanglement simultaneously.Further analysis shows that the unique characteristic depends strongly on the off-diagonal non-zero elements of the density matrix.Our result manifests the greater robustness of quantum discord compared with entanglement,which may be helpful in quantum-information technologies.

Characteristics of strong-coupling bipolaron qubit in two-dimensional quantum dot in electric field

Based on Lee-Low-Pines(LLP) unitary transformation, this article adopts the variational method of the Pekar type and gets the energy and wave functions of the ground state and the first excited state of strong-coupling bipolaron in two-dimensional quantum dot in electric field, thus constructs a bipolaron qubit. The numerical results represent that the time oscillation period T0 of probability density of the two electrons in qubit decreases with the increasing electric field intensity F and dielectric constant ratio of the medium η; the probability density Q of the two electrons in qubit oscillates periodically with the increasing time t; the probability of electron appearing near the center of the quantum dot is larger, while that appearing away from the center of the quantum dot is much smaller.

Low-temperature antiferromagnetic order of Ni_4 single-molecule magnets

The low-temperature specific heat of Ni4 single-molecule magnets (SMMs) is measured in a PPMS He-3 system. The tem- perature-dependent specific heat of Ni4 SMMs shows an antiferromagnetic phase transition at 0.91 K. The experimental results are in good consistency with Monte Carlo simulation of 3D-Ising model, indicating two independent diamond-like antiferro-magnetic structures with an exchange energy J = 0.020 K in Ni4 system.