Key Laboratory of Advanced Micro-Structured Materials of Ministry of Education, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 11874287, 11574229, 11774262), the National Basic Research Program of China (Grant No. 2016YFA0302800), and the Shanghai Science and Technology Committee (STCSM), China (Grant No. 18JC1410900).
Received Date:15 January 2019
Accepted Date:17 June 2019
Available Online:01 September 2019
Published Online:05 September 2019
Abstract:All-optical diodes and all-optical transistors are the basis of all-optical logic devices. We study the quantum statistical properties of all-optical diodes based on cavity quantum electrodynamics (QED)[1], and discuss the squeezed properties of the output light after passing through the diode when coherent light and squeezed light are incident. Here we extend our research to all-optical transistor, and take all-optical transistor based on cavity optomechanical system as the research object. By changing the intensity of classical pump light, the all-optical transistor can effectively control the output of the probe light and realize optical amplification. We discuss the squeezed properties of the output light of the all-optical transistor with squeezed light and coherent light as the probe light. Our results show that when the probe light is coherent, the output light remains coherent no matter whether it works in the amplified region, and is not squeezed. When the input probe light is amplitude squeezed light, the output light is still squeezed light in the light amplification region of all-optical transistor, but the squeezed properties are modulated by the input light squeezed properties and system parameters. When the squeezed angle of the input probe squeezed light is 0°, the minimum squeezed parameter S1 of the output squeezed light decreases with the increase of the squeezed coefficient r of the input probe light, and the minimum value approaches to the squeezed limit of –0.25. But the change of squeezed angle of the input probe squeezed light changes has a great influence on the squeezed parameter S1,2 of the output light, and the squeezed properties will disappear. Only when the squeezed angle is an integer multiple of π, will the squeezed properties of the output light be best. This result has a potential application value in quantum measurement, weak signal detection, and other fields. Keywords:all-optical transisitor/ squeeze light/ cavity optomechanical system
若$ {S}_{1}$和$ {S}_{2}$都为0, 则输出场为最小不确定度态, 也就是相干态. 如果$ {S}_{1}$和$ {S}_{2}$其中一个小于0, 则输出场为压缩态; 当$ {S}_{1}<0$时对应强度压缩, 而$ {S}_{2}<0$时则对应相位压缩. 要讨论输出光的压缩特性, 主要看$ {S}_{1}$和$ {S}_{2}$的值是否小于0. 采用图2中的系统参数来讨论在输入探测光为压缩光时该耦合系统输出光的压缩特性. 在图3中, 计算了不同压缩光(也就是压缩幅r设定为1, 2和3, 同时压缩角θ分别取0, ${\text{π}}/4 $, ${\text{π}}/2 $和$3{\text{π}}/4 $)作为输入探测光时, 输出光中的线性部分的压缩参数$ {S}_{1}$随探测光频率(探测光与腔模的失谐)的变化. 图 3 在输入的探测光为压缩光的情况下, 输出光的线性部分的压缩分量$ {S}_{1}$随有效探测-腔失谐量$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}={\omega }_{{\rm p}{\rm r}}-{\omega }_{{\rm c}}{'}$的变化, 探测压缩光的压缩角θ为(a) 0, (b) π/4, (c) π/2 (d) 3π/4 Figure3. When the input probe light is squeeze light, the squeeze component $ {S}_{1}$ of the linear part of the output light varies with the effective detection-cavity detuning value ($ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}={\omega }_{{\rm p}{\rm r}}-{\omega }_{{\rm c}}{'}$). The squeeze angle of the probe light is (a) 0, (b) π/4, (c) π/2 (d) 3π/4
当θ = 0时, 见图3(a), S1的值在所考虑的探测光频率范围内均小于0, 即都具有压缩性. 对于r = 1的输入压缩光(黑色实线), 输出光的$ {S}_{1}=$–0.21, 其值基本不随探测光的频率发生变化. 对于r = 2的输入压缩光(红色实线), 输出光的$ {S}_{1}$在探测光与腔模共振时, 即$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$, 达到最小值–0.246, 并随着失谐的增大而增大. 对于r = 3的输入压缩光(蓝色实线), 输出光的$ {S}_{1}$的值随着探测光频率的变化幅度更大, 但在探测光与腔模共振, 即$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$时, 也达到最小值, 且最小值为–0.2498, 接近压缩极限–0.25. 由此可见, 对于输入压缩光, 当压缩角θ = 0且频率与腔模共振$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$时, 输出光的$ {S}_{1}$具有最小值, 且这最小值随着输入压缩光的压缩幅r的增大而减小, 并接近压缩极限. 当$ \theta >0$时, 见图3(b)—图3(d), θ分别为π/4, π/2和3π/4, 输出光的$ {S}_{1}$都变得大于0. 随着θ的增加, $ {S}_{1}$的值也在增加. 由于$ {S}_{1}$都大于0, 输出光的X1不再具有压缩性. 图3中只讨论了输出光的$ {X}_{1}$的压缩参量$ {S}_{1}$. 对于输出光的$ {X}_{2}$的压缩参量$ {S}_{2}$, 计算的结果显示输出光的$ {S}_{2}$与$ {S}_{1}$的结果有一定的关联, 也就是θ分别取0, π/4, π/2和3π/4时的$ {\rm S}_{1}$与θ取π, 3π/4, π/2和π/4时的$ {\rm S}_{2}$结果相等. 话句话说, 输入压缩角为θ所得到的$ {S}_{1}$与压缩角为(π–θ)得到的$ {S}_{2}$相同. 所以只给出$ {S}_{1}$的结果. 可见在考虑的4个压缩角情况下, 只有当压缩角为π的整数倍的输入压缩光产生的输出光会存在压缩. 接下来, 在考虑输入探测光与腔模共振, 即$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$, 且入射压缩光的压缩角固定为θ = 0的情况下, 计算输出光中的线性部分的压缩量$ {S}_{1}$随入射压缩光压缩幅r的变化, 结果如图4所示. 当输入光压缩系数r = 0时也就是相关光入射, 输出光的压缩度也为0, 也是相干光. 当输入光压缩系数增大时, 输出光的$ {S}_{1}$小于0, 且$ {S}_{1}$的值随着r的增大单调减小, 输出光的压缩增加了. 继续增加输入光压缩幅, 输出光的$ {S}_{1}$趋向于稳定值–0.25, 接近压缩极限. 图 4 输出光的线性部分的压缩量$ {S}_{1}$随入射探测光的压缩幅r的变化, 入射探测光的压缩角为θ = 0, 频率与腔模共振$ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$ Figure4. The variation of the squeeze parameter S1 of the linear part of the output light with the squeeze amplitude r of the incident probe light, the squeeze angle of the incident probe light is θ = 0, and the frequency is resonant with the cavity mode $ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}=0$.
最后讨论输出光中的非线性部分. 固定入射探测压缩光的压缩角θ = 0, 图5计算了在不同压缩幅r的情况下, 输出光中的非线性部分的压缩量$ {S}_{1}$随探测光频率的变化. 图 5 在不同入射压缩光压缩幅的情况下, 输出光中的非线性部分的压缩量$ {S}_{1}$随入射探测压缩光频率的变化. $ {\varDelta }{'}_{{\rm p}{\rm r}{\rm c}}={\omega }_{{\rm p}{\rm r}}-{\omega }_{{\rm c}}{'}$为探测光与腔模的频率失谐 Figure5. The squeeze parameter S1 of the non-linear part of the output light varies with the frequency of the incident probe squeeze light in the case of different squeeze amplitudes of the incident squeeze light, $ \varDelta{'} _{\rm{prc}}={{\omega }_{\rm{pr}}}-\omega_{\rm{c}}{'}$ is the frequency detuning between the probe light and the cavity mode.