Effects of initial states on the quantum correlations in the generalized Grover search algorithm

We investigate the correlations between two qubits in the Grover search algorithm with arbitrary initial states by numerical simulation. Using a set of suitable bases, we construct the reduced density matrix and give the numerical expression of correlations relating to the iterations. For different initial states, we obtain the concurrence and quantum discord compared with the success probability in the algorithm. The results show that the initial states affect the correlations and the limit point of the correlations in the searching process. However, the initial states do not influence the whole cyclical trend.     

Storage and Retrieval of a Weak Optical Signal Improved by Spontaneously Generated Coherence in an Atomic Assemble

We investigate the reversible storage of a weak single-mode light signal in a Λ-type three-level atomic system with spontaneously generated coherence (SGC) and pumped by an incoherent field.The scheme is phase-dependent.If the phase of the controlling field is set oppositely to that of the signal field,the combination of SGC with weak pump overcomes the drawback of incompletely retrieval in the conventional scheme,leading to 100% retrieval fidelity or even to the amplification of the retrieved signal with respect to its initial one.     

微波射频场调制下Λ型三能级原子系统的电磁感应光栅

研究了在微波射频场调制下的Λ 型三能级原子系统的电磁感应光栅现象. 结果表明: 微波场可以增强对探测场的相位调制和增益作用, 使得衍射强度、尤其是一阶衍射强度明显提高; 当系统参数取值适当时, 一阶衍射强度随微波场强度呈指数增长的趋势. 关键词： 电磁感应光栅 电磁感应透明 微波射频场     

基于量子长短期记忆网络的量子图像混沌加密方案

近年来,图像信息的传输安全性已经成为互联网领域的重要研究方向.本文提出了一种基于量子长短期记忆(quantum long-short term memory, QLSTM)网络的量子图像混沌加密方案.结果发现,因为QLSTM网络具有复杂的结构和较多的参数,应用QLSTM网络对Lorenz混沌序列进行改进,其最大Lyapunov指数比原序列提高2.5465%,比经典长短期记忆(long-short term memory, LSTM)网络改进的序列提高0.2844%,同时在0—1测试中结果更接近1且更稳定,因此QLSTM网络改进的序列具备更优异的混沌性能,更难以被预测,提高了单一混沌系统加密的安全性.运用NCQI (novel quantum representation of color digital images)量子图像表示模型,将原始图像存储为量子态形式,利用QLSTM网络改进的序列分别控制三级径向扩散、量子广义Arnold变换和量子W变换,改变量子图像的灰度值与像素位置,生成最终的加密图像.本文提出的加密方案在统计学特性测试中,实现了RGB三通道平均信息熵均大于7.999,像...     

Controlling group velocity in a superconductive quantum circuit

We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit(SQC) pumped by microwave fields,and the use of such a SQC function as an artificial Λ-type three-level atom.The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity,and the superluminal state is usually realized with a lower absorption.This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.