【作者】 尹璋琦；

【导师】 李福利；

【作者基本信息】 西安交通大学 ， 光学， 2009， 博士

【摘要】 自从Shor算法的发明以来,量子信息学引起了人们极大的关注和兴趣。本文讨论了如何在光学腔系统中实现量子信息处理过程和制备光学器件。所谓量子信息处理包括量子态传输以及量子逻辑门的实现,以及量子纠缠态的制备。本文所考虑的光学腔系统包括腔QED系统和光学机械振子系统。在论文的第一部分,我们讨论了在腔QED系统中实现各种量子信息处理过程的理论方案。我们考虑的系统包括两个空间上远离的光学腔,通过单模光纤连接。(多)原子束缚在腔中,与腔模耦合,而腔模又同时与光纤模共振耦合。如果原子们与局域的腔场共振集体耦合,且原子之间没有直接相互作用,我们发现在相互远离的两团原子间可以实现完美的量子态传输,以及高度可靠的量子交换门,纠缠门和控制Z门。我们发现实现这些量子信息处理完成的速度随着原子数的增加而增大,而原子自发幅射和光子泄露等耗散过程对量子信息处理的影响被极大的压缩了。我们提出如何在这个系统中制备一个可控的有效压缩真空库环境。然后我们表明仅通过绝热的操控库环境参数,可以在两个相互远离的腔中束缚的原子之间实现控制相位门和纠缠门。这个方案把在非消相干子空间中操控库环境和几何相位量子计算综合到一起了,具有如下重要特点：任意相位的控制相位门都可以仅仅通过简单的改变控制光场的强度和相对相位来实现；利用纠缠门可以高效的制备出稳定的两量子比特的最大纠缠态,而不需要通过测量。在本文的第二部分,我们讨论了如何在光机械系统中制备非经典光,以及如何冷却它。在光机械系统中,我们提出了一个在两个相位振幅正交的光学模式之间制备连续变量纠缠光的方案。在合适的驱动功率和失谐量下,纠缠度对热库温度和机械振子的品质因子Q都不敏感。在实际可行的实验条件下,我们发现即使是室温下做实验,纠缠度也可以非常的高。此外,如果我们想冷却光机械振子,冷却激光的相位噪声对冷却纳米机械振子到量子区域设置了一个主要的技术难题。基于振子与两个光学模式同时耦合的模型,我们提出了一个冷却方案设置,可以极大的减小相位噪声的影响,消除相位噪声对冷却机械振子到量子区域的限制。经过对各种参数进行优化后,我们由简单的估计表明光机械振子冷却的内禀极限由如下式子确定：Tenv/Q,其中Tenv是环境温度,而Q是机械振子品质因子。我们也讨论了当机械振子冷却到量子区域附近时,如何探测声子数,并确定了完成这个探测所需满足的条件。更多还原

【Abstract】 Quantum information science has attracted a lot of attentions since the invention of Shor’s algorithm. The thesis focuses on realizing the quantum information processes and optical devices in optical cavity system, such as cavity QED systems and opto-mechanical systems. Here the quantum information processes include the quantum state transfer, quantum logic gates and generating quantum entangled states.In the first part of the thesis, schemes to realize quantum information processes in cavity QED systems are discussed. We consider the systems containing two remote cavities, which are connected by an optical fiber. (Multi) Atoms are trapped in the cavities and couple with the cavity modes, which resonantly couple with the fiber mode. If the atoms resonantly and collectively interact with the local cavity fields but there is no direct interaction be-tween the atoms, we show that an ideal quantum state transfer and highly reliable quantum swap, entangling, and controlled-Z gates can be deterministically realized between the dis-tant cavities. We find that the operation quantum information processes can be greatly speeded up, and the effects of spontaneous emission of atoms and photon leakage out of cavity can also be greatly diminished as number of the atoms in the cavities increases. We also show that an effective squeezing reservoir can be engineered in the system under appro-priate conditions. Then we show that a two-qubit geometric CPHASE gate and entangling gate between the atoms in the two cavities can be implemented through adiabatically ma-nipulating the engineered reservoir. This scheme that combines engineering environment with decoherence-free space and geometric phase quantum computation together has the remarkable features:a CPHASE gate with arbitrary phase shift is implemented by simply changing the strength and relative phase of the driving fields, and entangling gate can generate stable extremely entangled two-qubit state without measurement.In the second part of the thesis, non-classical light source and cooling scheme in opto- mechanical systems are discussed. We propose a scheme to produce continuous variable en-tanglement between phase-quadrature amplitudes of two light modes in an opto-mechanical system. For proper driving power and detuning, the entanglement is insensitive with bath temperature and Q of the mechanical oscillator. Under realistic experimental conditions, we find that the entanglement could be very large even at room temperature. The noise from laser phase fluctuation sets a major technical obstacle to cool the nano-mechanical oscillators to the quantum region. We propose a cooling configuration based on the opto-mechanical coupling with two cavity modes to significantly reduce this phase noise. After optimization of the cavity parameters, we show through simple arguments that the intrinsic cooling limit of the opto-mechanical oscillator is set by Tenv/Q, where Tenv is the environ-ment temperature and Q is the mechanical quality factor. We also discuss detection of the phonon number when the mechanical oscillator is cooled near the quantum region and specify the required conditions for this detection.更多还原