【作者】 杨成；

【导师】 武海斌； 盛继腾；

【作者基本信息】 华东师范大学 ， 光学， 2022， 博士

【摘要】 腔光力学作为当前一个重要的研究前沿领域,为光子和声子操控提供了有效的研究平台。腔光力学在实验上已经实现了宏观振子的量子基态冷却和宏观量子纠缠等,同时在量子精密测量与传感、相干波长转换、相干声子存储等应用技术上取得突破,这使得腔光力学在宏观量子力学、动力学卡西米尔效应、引力波和暗物质探测等基础物理研究方面有着显著优势,也为将来量子技术应用提供了新的可能。宏观尺度的平衡热力学研究已经相当完善,然而当系统小到微纳尺度时,系统的热力学涨落变得尤为重要,动力学过程呈现非平衡随机特性。随机热力学作为统计力学研究的一个重要的基础领域,为研究和理解小系统的非平衡热力学提供了基础。非平衡状态下沿着轨迹的热力学能量转移和熵产生以及随机热机的实现和做功效率的研究是随机热力学研究的重要方面,对从微纳尺度上研究和理解非平衡统计物理具有重要的意义。腔光力学基于腔光场模式和力学振动模式间的光力相互作用,能够在极为广泛的物理系统中实现。集成纳米薄膜振子的腔光力学体系,具有高度的可控性和可扩展性,并且高品质的纳米薄膜振子,可以作为高灵敏的传感元件,在实验研究和实际应用中表现出明显的优势;同时在热驱动下的纳米薄膜振子具有显著的随机动力学特性,可作为一个天然的随机热力学研究对象,因此,腔光力学体系成为随机热力学研究的理想平台。本论文从实验上搭建了在光学腔内集成两片空间分离的纳米薄膜振子的腔光力学实验装置,两个纳米振子分别与高温热库和低温热库相接触,且同时与一个共同的腔模光场发生光力相互作用,在远红失谐的激光泵浦下,可实现两个分离的纳米振子间由腔光场调控的相干耦合。在非平衡热库的驱动下,系统进入非平衡状态,通过对腔光场的调控并结合高灵敏的光学位移探测技术对两个振子运动进行实时单独地测量,有效地开展了如下在随机热力学方面关于非平衡声子热输运和纳米随机热机的实验研究:1.腔光场调控的力学振子间非平衡声子热输运实验研究非平衡热力学中热传输研究是一个重要的研究前沿,对于发展新型热调控器件有非常重要的意义。通常的热能量传输主要有热对流、热传导和热辐射三种形式。实验上,通过腔增强的长程相互作用耦合两个在空间上分离的纳米力学振子,实现了一种腔光场调控的新型声子热传输机制。两纳米力学振子系统在非平衡温度梯度驱动下远离平衡并在光场作用下,自发产生热流,尤其在强耦合时,非平衡稳态的瞬时热流呈现往复的振荡行为,并伴随着从低温热库流向高温热库的反常瞬时热流。在此基础上,非平衡稳态下,对热流精度的普适约束,即热力学不确定关系,在实验上得到验证。实验结果使得人们对纳米振子的热传输特性有了深刻的认识,也为深入检验非平衡热力学基本原理提供了一个有效的研究平台。2.基于腔光场调控的力学振子的耦合模纳米随机热机实验研究当前微纳尺度的随机热机是一个非常重要的研究方向,实验上我们利用由腔光场调控下强耦合的两片纳米薄膜振子体系的本征模式作为做功介质,构建Otto热力学循环,在两个声子热库中抽取热能转变为对外做功,首次同时实现了分别由系统的上支本征模对外做功的单缸热机和上下支本征模交替对外做功的双缸热机,并发现了振子关联在热力学循环中的重要作用。热机在每次循环时初态声子数是涨落的,使得热机呈现随机特性。实验研究结果证明了这一类在腔光力学系统中极其重要的热机,为进一步开展纳米随机热机和可控可扩展的基于小系统相互作用体系的热机研究提供了理想平台。本论文基于多模腔光力体系开展了腔光场调控的非平衡声子热输运和耦合模纳米随机热机的实验研究,使得我们对非平衡状态下的热输运有了更为深入的理解和认识,对微纳随机热机的特性和提升热能转化效率的研究有重要意义,也为腔光力学领域进一步在开展微纳尺度的随机热力学和量子热力学研究提供了新的借鉴。更多还原

【Abstract】 Cavity optomechanics as an important current research frontier provides an effective research platform for the manipulation of photon and phonon.Experimentally,cavity optomechanics has achieved quantum ground state cooling of macroscopic oscillators and macroscopic quantum entanglement,and has also made breakthroughs in applied technologies such as quantum precision measurement and sensing,coherent wavelength conversion,coherent phonon storage,etc.This gives cavity optomechanics a significant advantage in fundamental physics research on macroscopic quantum mechanics,dynamical Casimir effect,gravitational waves and dark matter detection,and also provides new possibilities for future quantum technology applications.The study of equilibrium thermodynamics at the macroscopic scale is quite well established,however,when the system is small to the micro/nano scale,the thermodynamic fluctuation of the system becomes particularly important and the dynamical processes exhibit a non-equilibrium stochastic characteristics.Stochastic thermodynamics,an important fundamental area of statistical mechanics research,provides the basis for the study and understanding of nonequilibrium thermodynamics of small systems.The study of thermodynamic energy transfer and entropy generation along trajectories in non-equilibrium state,as well as the implementation of stochastic heat engines and work efficiency,are important aspects of stochastic thermodynamics research and are of great significance for studying and understanding non-equilibrium statistical physics at the micro/nano scale.Cavity optomechanics is based on the optomechanical interaction between cavity optical field and mechanical vibrational modes and can be implemented in an extremely wide range of physical systems.The cavity optomechanical system integrating nanomembrane resonators is highly controllable and scalable,and high-quality nanomembrane resonators which can be used as highly sensitive sensing elements,have obvious advantages in experimental research and practical applications.At the same time,the nanomembrane resonators under the thermal driving have the remarkable features of stochastic dynamics and can be used as a natural object of stochastic thermodynamic research.Thus,the cavity optomechanical system becomes an ideal platform for investigating the research of stochastic thermodynamics.In this thesis,a cavity optomechanical setup is experimentally constructed by integrating two spatially separated nanomembrane resonators inside an optical cavity.The two nanoresonators are in contact with a high-temperature thermal reservoir and a low-temperature thermal reservoir and simultaneously interact with a common cavity optical field.Coherent coupling between two separated nanoresonators mediated by the cavity optical field can be achieved when the cavity is pumped by a far-red detuned laser.Driven by a non-equilibrium thermal reservoirs,the system enters a non-equilibrium state.By controlling the cavity optical filed and combining it with highly sensitive optical displacement detection techniques measuring the motion of two resonators individually and in real time,the following experimental studies on non-equilibrium phonon heat transport and nanometre-sized stochastic heat engines in stochastic thermodynamics have been effectively carried out:1.Experimental study of non-equilibrium phonon heat transport between cavity-mediated mechanical resonatorsThe study of heat transport in non-equilibrium thermodynamics is a crucial research frontier and is of great importance for the development of new thermal regulation devices.The three major conventional forms of heat transfer are thermal convection,thermal conduction and thermal radiation.Experimentally,a novel mechanism of cavity-mediated phonon heat transport is realized by coupling two spatially separated nanomechanical resonators by the cavityenhanced long-range interactions.The system of two nanomechanical resonators are driven away from equilibrium state by a non-equilibrium temperature gradient and spontaneously generates the heat flux under the action of the optical field.In particular,at strong coupling,the non-equilibrium steady-state instant heat flux exhibits the behaviour of oscillation back and forth and is accompanied by anomalous instant heat flux from the low-temperature thermal reservoir to the high-temperature thermal reservoir.On this basis,the universal constraint on the precision of the heat flux in the non-equilibrium steady state,i.e.the thermodynamic uncertainty relation,is experimentally verified.The experimental results provide insight into the heat transport properties of nanoscopic resonators and provide an effective research platform for an in-depth test of the fundamental principles of non-equilibrium thermodynamics.2.Experimental study of coupled-mode nanometre-sized stochastic heat engines based on cavity-mediated mechanical resonatorsThe stochastic heat engines in micro/nano scale are currently a very important research direction.Experimentally,we uses the normal modes of the cavity-mediated strongly coupled nanoresonators as the working medium and construct an Otto cycle for extracting heat energy into doing work between two phononic thermal reservoirs.For the first time,a single-cylinder heat engine using the upper normal mode of the system to do work and a two-cylinder heat engine with upper and lower normal modes alternatively doing external work are simultaneously realized,respectively.The important role of the correlation between two resonators during the thermodynamic cycle is also discovered.The number of initial phonons fluctuates throughout each cycle of the heat engines,so the heat engines exhibit stochastic properties.The experimental results demonstrate an essential class of heat engine in cavity optomechanical systems and provide an ideal platform for further development of nanometre-sized stochastic heat engines and investigating heat engines of interacting subsystems in small scales with controllability and scalability.This thesis carries out the experimental studies of cavity-mediated nonequilibrium phonon heat transport and coupled-mode nanometre-sized stochastic heat engines based on the multimode cavity optomechanical system,which enable us to gain a deeper understanding and knowledge of thermal transport in non-equilibrium state,and are of great significance to the study of the properties of micro/nanometre-sized stochastic heat engines and the enhancement of thermal energy conversion efficiency.It also provides a new reference for further research on the stochastic thermodynamics and quantum thermodynamics at the mico/nano scale in the field of cavity optomechanics.更多还原