基于腔量子电动力学的光机械系统与自旋压缩研究

发布时间：2018-03-25 20:09

本文选题：腔量子电动力学　切入点：腔光机械　出处：《中国科学技术大学》2015年博士论文

【摘要】：信息科学是研究信息运动规律和应用方法的科学,近30年来,信息科学与量子力学相结合而兴起的量子信息科学受到了广泛的关注。量子信息科学由于一些新奇特性,比如量子态的不可克隆性、线性叠加性、纠缠特性等,使其在量子计算、量子信息、量子度量等方面显示出十分广阔技术应用前景。量子计算机的并行处理能力使其计算速度远远快于经典计算机,在密码破解、量子搜索等方面展示出了巨大的潜力。量子信息利用量子态不可被克隆性、纠缠特性等特点已经在量子密码、量子通信等实用化领域取得了重大的进展。测量高精度物理量的需求推动了量子度量学的发展,在量子时钟和引力探测等领域的研究也越来越热,在有些领域已经突破了经典物理的极限,正在向着海森堡极限逼近。量子信息科学的优势吸引着人们寻求各色各样的信息载体来实现量子计算机。量子计算机在物理实现上需要考虑各种折衷因素,在离子阱、超导电子电路、线性光学、腔量子电动力学装置和分子核磁共振等系统中已经取得了很大的进展。但是实际量子物理体系中会有各种各样的耗散,而且量子比特数目越多耗散会越严重。幸运的是有些体系在某些方面的优势非常明显,因此混合物理系统也受到了越来越多的关注。腔光机械系统在量子信息存储、量子混沌、波长转换等方面有很大的潜在应用前景,特别是其与原子或者量子点等耦合形成的混合物理体系,更是近年来研究的一个热点。腔量子电动力学(C-QED)是研究原子和光学模式之间相互耦合的一个重要领域。在高品质因子的光学腔中,光子与原子可以进行多次相互作用,实现原子与光场很强耦合,从而制备自旋压缩态(SSS)用于量子度量。在本篇论文中,我们首先简要介绍量子信息科学的一些基本知识,讨论了腔光机械系统和腔量子电动力学装置。对于腔光机械系统,我们研究了该系统一些基本性质和应用,还分析了其与量子点耦合形成的混合物理体系、单光子和双光子的输入输出、声子激光。对于腔量子电动力学装置,我们就制备自旋压缩态方面做了详细的讨论,主要包括以下几点：在腔压缩体系中通过失谐来加强自旋压缩；在氮-空穴(NV)色心体系中基于几何相位通过声子诱导自旋压缩；通过连续驱动NV自旋链产生压缩稳态。具体内容为如下四个方面：1.腔光机械系统研究腔光机械系统是实现量子通信和量子计算一个非常重要的系统,里面有丰富的物理现象和很多潜在的应用。我们在光机械诱导透明、布里渊散射诱导透明以及非互易光存储等方面做了一些简单的讨论。在光机械与量子点耦合形成的混合物理体系中,我们发现了真空腔诱导透明现象,从强弱耦合两个角度做了详细的分析。此外,我们还将经典控制光与真空腔诱导下的透明现象做了对比。最后,为了能更好地理解诱导透明现象,我们在一般三能级原子体系中,通过非相干控制实现了电磁诱导透明(EIT)与Autler-Towns劈裂(ATS)的相互转换,并对两者做了区分。在光机械的输入输出研究中,我们得到了在平方耦合的情况下单光子的输出谱,其展现出声子偶数激发的特点。以此为基础,我们进一步研究了在实空间下双光子的输入输出情况。对于声子激光,我们提出了几个可行的实现方案。2.失谐加强腔自旋压缩我们理论上详细讨论了实验上已经实现的腔自旋压缩方案中各个参数对自旋压缩的影响,与近共振的方案相比,我们发现失谐可以将腔压缩度从原来的S一2／5大幅度提高到S-2/3,其中S是总自旋数。此外,我们还发现原子和腔之间弱的相互作用和大失谐可以加强原子系综的自旋压缩。解析结果表明,自旋压缩来源于由激光驱动诱导的与自旋态相关的几何相位,因此在这里大失谐非常重要。对于实际的物理系统来说,一些噪声是不可避免的。我们分析了由于原子拉曼散射对自旋压缩所产生的影响,结果表明通过合适的失谐可以优化自旋压缩。大失谐激光驱动使进入到光学腔中的有效光场减少,因此需要更长的时间才能达到最优的压缩。在这种情况下,单自旋退相干不得不考虑,我们发现更强的驱动光可以有效的减弱这种噪声对自旋压缩的破坏。大失谐激光驱动也有可能激发光学腔的其他光学模式,我们对多模式光场与原子系综的耦合也做了详细的讨论,发现其它光场模式对自旋压缩的影响完全可以忽略。最后,我们将实验上可实现的参数代入方案中,其结果说明通过失谐的调节来加强自旋压缩在目前的实验条件下很容易实现。作为产生自旋压缩的一个补充,基于此方案我们对通过测量来实现非经典态也做了一些讨论。3.氮-空穴(NV)色心体系中基于几何相位的声子诱导自旋压缩我们提出了一个通过单机械模式诱导几何相位的方案来实现自旋压缩,在这里NV链散射耦合到单机械振子上。几何相位由于其自身的属性,对声子的初态非常不敏感,这是实验上一个非常重要的优势。我们研究了在不同的热噪声和机械品质因子(Q)下的自旋压缩性质,结果表明完美单轴压缩可以在热噪声和机械品质因子合适的比值下实现。在实际的物理体系中,NV链会与一些热库耦合,这种耦合引起了退相干,因此对自旋压缩产生了破坏。我们通过动力学退耦合脉冲序列来抑制这种热库对自旋压缩的影响,在高品质因子的金刚石氮-空穴自旋链中,我们可以实现完美的单轴自旋压缩。最后,我们还提出了一些实验上可行性的方案,还对一些实验上已经实现的参数做了一些分析,结果表明我们提出的方案在目前的实验条件下是可行的。4.通过连续驱动氮-空穴(NV)自旋链产生压缩稳态在NV自旋链全同地耦合到同一个光学模式的系统中,我们提出了通过连续光驱动NV自旋来产生自旋压缩稳态的方案。在满足一定频率匹配的条件下,我们通过旋波近似得到了系统的有效哈密顿量。该有效哈密顿量表明集体NV自旋暗态的存在,通过对这种暗态的研究,我们发现该暗态就是自旋压缩态。这种自旋压缩态可以通过光场的耗散方式来制备,因此耗散在这里成为了相干的来源。我们研究了在驱动光不同频率和强度下自旋压缩稳态的情况,频率越大满足旋波近似的条件越好,自旋压缩的动态波动越小,压缩也越好,但是其最后趋于稳定的压缩完全取决于驱动光的强度。此外,我们也分析了光子噪声对压缩的影响。最后,我们讨论了这种方案在频率失配下的自旋相变现象。
[Abstract]:Information science is the study of information movement and the application of the method of science, in the past 30 years, the combination of information science and quantum mechanics of quantum information science and the rise has attracted widespread attention. Quantum information science because of some novel properties, such as quantum non clone, linear superposition, entanglement,. In quantum computation, quantum information, quantum measurement shows a very broad application prospect. The parallel processing ability of quantum computer to calculate much faster than classical computers, the password is cracked, quantum search and other aspects show great potential. The use of quantum information quantum state can not be cloned, entanglement characteristics in quantum cryptography, quantum communication and other practical fields and made great progress. The high precision measurement of physical quantity needs to promote the development of quantum metrology, in quantum clock and Research in the field of gravity detection is more and more hot in some areas has exceeded the limit of classical physics, is toward the approaching Heisenberg limit. The information carrier of quantum information science advantages to attract people to seek to achieve the diversiform quantum computer. The quantum computer needs to consider various factors on the physical realization of compromise, in an ion trap, superconducting electronics circuit, linear optics, much progress has been made in cavity quantum electrodynamics and NMR systems. But the actual dissipative quantum physical systems in various, and the number of qubits more dissipation will be more severe. Fortunately some advantages in some aspects of the system is very obvious, so mixed physical system has attracted more and more attention. Optomechanical system in quantum information storage, quantum chaos, aspects of wavelength conversion is big The potential application prospect, especially the mixed physical system formation and coupling of atoms or quantum dots, it is a research hotspot in recent years. The cavity quantum electrodynamics (C-QED) is between atom and optical mode coupling is an important field in the optical cavity. High quality factor, photons and atoms can be multiple interactions, the atoms and the light field is strong coupling, thereby preparing spin squeezed state (SSS) for quantum measurement. In this thesis, we first briefly introduce some basic knowledge of quantum information science, discusses the mechanical system and optical cavity quantum electrodynamics. The optical mechanical system, we study the system of some basic properties and application, analyzes its formation and hybrid physical system coupled quantum dots, input and output, single and two photon phonon laser for cavity quantum electrodynamics. We have prepared device, spin squeezed state are discussed, mainly including the following: in the cavity compression system by detuning to strengthen spin squeezing; in nitrogen vacancy (NV) center system based on geometric phase by spin phonon induced by continuous compression; drive NV spin chain to produce steady compression specific contents into four aspects as follows: 1. cavity optical mechanical system of optical mechanical system is the realization of quantum communication and quantum computing is a very important system, there are abundant physical phenomena and many potential applications. We are in the light mechanical induced transparency, Brillouin scattering induced transparency and non reciprocal optical storage and so on do some simple discussion. Hybrid physical system formed in the coupling of mechanical and quantum dots, we found that the vacuum cavity induced transparency phenomenon from two aspects in detail the coupling strength Analysis. In addition, we will also control the classic transparent phenomenon of light with the vacuum chamber under the induction were compared. Finally, in order to better understand the induced transparency phenomenon, we in general three level atomic system, the non coherent control of electromagnetically induced transparency (EIT) and Autler-Towns splitting (ATS) conversion of the two, and made a distinction between input and output. In the light of the machine, we get the output in the case of a single photon coupled square spectrum, which shows the characteristics of even phonon excitation. On this basis, we further study the input and output of double photon in real space. For phonon laser, we put forward several feasible scheme of.2. cavity detuning strengthen spin squeezing theory we discussed each parameter has been achieved on experimental spin cavity compression scheme on spin compression effect, and the near resonance Compared, we found the detuning can be compressed from a S cavity of 2 / 5 greatly increased to S-2/3, where S is the total number of spins. In addition, we also found that the interaction between the atoms and the cavity is weak and large detuning can strengthen spin atomic ensemble compression. The results show that the spin the compression comes from the laser driven and spin state geometric phase induction, so here the large detuning is very important for the actual physical system, some noise is inevitable. We analyzed the Raman scattering on atomic spin squeezing the influence, the results show that the appropriate detuning can optimize the spin compression. Large detuning laser drive into the optical cavity of the light field effectively reduced, therefore need longer time to achieve optimal compression. In this case, the single spin decoherence had to be taken into account, we find more Strong driving light can reduce this noise effectively on spin squeezing damage. Large detuned laser driver may also be emitting other optical cavity model, we on multi mode light field and atomic ensembles coupling also discussed in detail, find other light field of spin squeezing can be we will be ignored. Finally, parameters can be realized on the experimental scheme, the results show that by adjusting the detuning to enhance the spin squeezing is easy to implement in the present experimental conditions. As a supplement to produce spin compression, based on this scheme we measured by non classical states have done some discussion.3. nitrogen vacancy (NV) phonon geometric phase induced spin compression we propose a mechanical model induced by single geometric phase scheme to realize spin compression based on center system, here NV chain scattering Coupled to a single mechanical oscillator. The geometric phase because of its own property, the initial state is not sensitive to the phonon, this is a very important advantage of experiment. We studied the thermal noise and mechanical quality factor (Q) under different spin squeezing properties, results show that perfect uniaxial compression can be achieved the ratio of thermal noise and mechanical quality factor appropriate. In the physical system, NV chain and some thermal reservoir coupling, the coupling caused by decoherence, resulting in damage to the spin squeezing through our dynamic decoupling pulse sequences to suppress the thermal reservoir effect on spin squeezing, in diamond nitrogen high quality factor - hole spin chain, uniaxial compression spin we can achieve perfect. Finally, we present some experiments on the feasibility of the scheme, the parameters of some experiments has made some Analysis results show that our proposed scheme in the present experimental conditions is feasible by.4. nitrogen hole continuous drive (NV) spin chain produce compression homeostasis in NV spin chain with coupled to the system with an optical model, we put forward by continuous light driven NV to generate spin spin squeezing state scheme. Under certain frequency matching conditions, we obtained by rotating wave approximation effective Hamiltonian. The effective Hamiltonian that collective NV spin dark state, through the study of this dark state, we found that the dark state is spin squeezed state. By way of field dissipation the preparation of this spin squeezed state, thus became the source of coherent dissipation here. We studied in the light of different driving frequency and intensity under steady-state conditions of spin squeezing, the greater the frequency to meet the conditions of the rotating wave approximation The better dynamic fluctuation of spin squeezing decreases, compression is also better, but the final stable compression depends entirely on the driving light intensity. In addition, we also analyzed the influence of photon noise on compression. Finally, we discuss the scheme in the frequency distribution of the spin transition phenomenon.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O413.2

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