量子谐振子与经典谐振子的比较

在Heisenberg表象，通过引入升降算符求解了量子谐振子，计算了任意初态情况下坐标、动量、动能、势能和哈密顿量的期望值，并同经典谐振子的相应力学量进行了比较，得出了量子谐振子只能在一定条件下趋近于经典谐振子而不可能等同。     

量子谐振子与量子系统的经典极限

以一维量子谐振子为例，经过分析，认为量子系统经典极限条件也可表示为h→0。     

均匀磁场中三维各向同性带电谐振子的双波函数描述

讨论均匀磁场中三维各向同性带电谐振子的双波函数描述,得到量子和经典极限条件下的结果。     

电磁场及二维谐振子场中运动电子的双波与经典描述

研究了有旋非相对论性电子在相互垂直的均匀电磁场及二维谐振子场中运动的量子双波描述，得到了量子结果及其经典极限，并与纯经典情况相比较，获得了两者的一致性．     

SU(2)q-奇偶相干叠加态的非经典效应

由一维线性谐振子引入q—形变谐振子，构成旷形变谐振子的量子Heisenberg-Weyl代数，构造了SU(2)q-奇偶相干叠加态，计算了在此态下的期望值，通过理论计算作图研究了其非经典效应．发现由于形变参数的影响，其压缩效应和反聚束效应具有丰富的结构。     

qs变形非简谐振子奇偶广义相干态及其量子统计特性

利用变换算符导出了qs变形的非简谐振子代数,得到了qs变形非简谐振子光场的广义相干态,研究了qs变形非简谐振子奇偶广义相干态的高阶压缩效应和反聚束效应,并用数值计算方法讨论了变形参数q和s对这些量子统计特性的影响。结果表明,qs变形非简谐振子奇偶广义相干态均可呈现奇次方阶压缩效应和反聚束效应,当q和s取一定值时,在qs变形非简谐振子光场强度取值的一定范围内,呈现这些非经典特性的范围随着q偏离1越大和s取值越小而变大。     

相干态与场的经典——量子对应

通过对电磁场和谐振子的量子化类比,论述用能量本征态表示量子化的电磁场,不满足场的经典——量子对应关系,若用相干态表示电磁场的量子态,则能满足对应原理的要求等。     

耦合谐振子的量子绝热捷径设计

量子绝热捷径技术旨在加快量子绝热慢过程, 已经被广泛用于原子的冷却、转移等量子信息处理过程. 研究耦合谐振子模型的量子绝热捷径设计及其热机应用, 基于耦合谐振子模型的量子不变量, 首先得到 Ermakov 方程, 然后反设计耦合谐振子频率, 最终加快绝热过程而不产生末态激发. 本工作为耦合谐振子的量子态操控及超绝热量子热机提供了新思路.     

度量算符对Gauss编织态作用的期望值

圈量子引力是主要的候选量子引力理论,考虑它和经典极限对应的连续极限是非常有趣的,Gauss编织态描述了一个半经典图景.本文计算了度量算符对Gauss编织态作用的表示矩阵元及其期望值,并且在该态的峰值区(p=1)、内腿颜色k=0的情况下,给出Gauss编织态顶角处毗邻的4切矢量间的夹角以及切矢量的长度.     

qs变形非简谐振子奇偶广义相干态及其量子统计特性

利用变换算符导出了qs变形的非简谐振子代数，得到了qs变形非简谐振子光场的广义相干态，研究了qs变形非简谐振子奇偶广义相干态的高阶压缩效应和反聚束效应，并用数值计算方法讨论了变形参数q和s对这些量子统计特性的影响。结果表明，qs变形非简谐振子奇偶广义相干态均可呈现奇次方阶压缩效应和反聚束效应，当q和s取一定值时，在qs变形非简谐振子光场强度取值的一定范围内，呈现这些非经典特性的范围随着q偏离1越大和s取值越小而变大。     

Generation of Fock states in a superconducting quantum circuit

Spin systems and harmonic oscillators comprise two archetypes in quantum mechanics. The spin-1/2 system, with two quantum energy levels, is essentially the most nonlinear system found in nature, whereas the harmonic oscillator represents the most linear, with an infinite number of evenly spaced quantum levels. A significant difference between these systems is that a two-level spin can be prepared in an arbitrary quantum state using classical excitations, whereas classical excitations applied to an oscillator generate a coherent state, nearly indistinguishable from a classical state. Quantum behaviour in an oscillator is most obvious in Fock states, which are states with specific numbers of energy quanta, but such states are hard to create. Here we demonstrate the controlled generation of multi-photon Fock states in a solid-state system. We use a superconducting phase qubit, which is a close approximation to a two-level spin system, coupled to a microwave resonator, which acts as a harmonic oscillator, to prepare and analyse pure Fock states with up to six photons. We contrast the Fock states with coherent states generated using classical pulses applied directly to the resonator.     

二维谐振子的双波函数描述

用双波函数的量子理论研究二维谐振子力学量的时间演化方程及经典近似 ,证明了二维各向同性谐振子角动量守恒     

Nanometre-scale displacement sensing using a single electron transistor

It has been a long-standing goal to detect the effects of quantum mechanics on a macroscopic mechanical oscillator. Position measurements of an oscillator are ultimately limited by quantum mechanics, where 'zero-point motion' fluctuations in the quantum ground state combine with the uncertainty relation to yield a lower limit on the measured average displacement. Development of a position transducer, integrated with a mechanical resonator, that can approach this limit could have important applications in the detection of very weak forces, for example in magnetic resonance force microscopy and a variety of other precision experiments. One implementation that might allow near quantum-limited sensitivity is to use a single electron transistor (SET) as a displacement sensor: the exquisite charge sensitivity of the SET at cryogenic temperatures is exploited to measure motion by capacitively coupling it to the mechanical resonator. Here we present the experimental realization of such a device, yielding an unequalled displacement sensitivity of 2 x 10(-15) m x Hz(-1/2) for a 116-MHz mechanical oscillator at a temperature of 30 mK-a sensitivity roughly a factor of 100 larger than the quantum limit for this oscillator.     

谐振子与薛定谔相干态及不确定度

薛定谔相干态被定义为其坐标与动量平均值的演化与经典解相同的量子态。证明谐振子的任何状态都是薛定谔相干态。并计算了它们的不确定度,指出最小不确定度的态正是Ｇｌａｕｂｅｒ相干态,同时证明了对非谐振子一般不存在薛定谔相干态。     

Laser cooling of a nanomechanical oscillator into its quantum ground state

The simple mechanical oscillator, canonically consisting of a coupled mass-spring system, is used in a wide variety of sensitive measurements, including the detection of weak forces and small masses. On the one hand, a classical oscillator has a well-defined amplitude of motion; a quantum oscillator, on the other hand, has a lowest-energy state, or ground state, with a finite-amplitude uncertainty corresponding to zero-point motion. On the macroscopic scale of our everyday experience, owing to interactions with its highly fluctuating thermal environment a mechanical oscillator is filled with many energy quanta and its quantum nature is all but hidden. Recently, in experiments performed at temperatures of a few hundredths of a kelvin, engineered nanomechanical resonators coupled to electrical circuits have been measured to be oscillating in their quantum ground state. These experiments, in addition to providing a glimpse into the underlying quantum behaviour of mesoscopic systems consisting of billions of atoms, represent the initial steps towards the use of mechanical devices as tools for quantum metrology or as a means of coupling hybrid quantum systems. Here we report the development of a coupled, nanoscale optical and mechanical resonator formed in a silicon microchip, in which radiation pressure from a laser is used to cool the mechanical motion down to its quantum ground state (reaching an average phonon occupancy number of 0.85 ± 0.08). This cooling is realized at an environmental temperature of 20?K, roughly one thousand times larger than in previous experiments and paves the way for optical control of mesoscale mechanical oscillators in the quantum regime.     

Real-time quantum feedback prepares and stabilizes photon number states

Feedback loops are central to most classical control procedures. A controller compares the signal measured by a sensor (system output) with the target value or set-point. It then adjusts an actuator (system input) to stabilize the signal around the target value. Generalizing this scheme to stabilize a micro-system's quantum state relies on quantum feedback, which must overcome a fundamental difficulty: the sensor measurements cause a random back-action on the system. An optimal compromise uses weak measurements, providing partial information with minimal perturbation. The controller should include the effect of this perturbation in the computation of the actuator's operation, which brings the incrementally perturbed state closer to the target. Although some aspects of this scenario have been experimentally demonstrated for the control of quantum or classical micro-system variables, continuous feedback loop operations that permanently stabilize quantum systems around a target state have not yet been realized. Here we have implemented such a real-time stabilizing quantum feedback scheme following a method inspired by ref. 13. It prepares on demand photon number states (Fock states) of a microwave field in a superconducting cavity, and subsequently reverses the effects of decoherence-induced field quantum jumps. The sensor is a beam of atoms crossing the cavity, which repeatedly performs weak quantum non-demolition measurements of the photon number. The controller is implemented in a real-time computer commanding the actuator, which injects adjusted small classical fields into the cavity between measurements. The microwave field is a quantum oscillator usable as a quantum memory or as a quantum bus swapping information between atoms. Our experiment demonstrates that active control can generate non-classical states of this oscillator and combat their decoherence, and is a significant step towards the implementation of complex quantum information operations.     

氢原子的基态经典振子模型

根据量子力学关于氢原子基态角动量为零的预言，将基态氢原子处理成经典一维振子模型，利用一种带相位因子和斥力项的势函数，给出了基态氢原子的能量及电子振动轨道的解析式。     

Quantum-coherent coupling of a mechanical oscillator to an optical cavity mode

Optical laser fields have been widely used to achieve quantum control over the motional and internal degrees of freedom of atoms and ions, molecules and atomic gases. A route to controlling the quantum states of macroscopic mechanical oscillators in a similar fashion is to exploit the parametric coupling between optical and mechanical degrees of freedom through radiation pressure in suitably engineered optical cavities. If the optomechanical coupling is 'quantum coherent'--that is, if the coherent coupling rate exceeds both the optical and the mechanical decoherence rate--quantum states are transferred from the optical field to the mechanical oscillator and vice versa. This transfer allows control of the mechanical oscillator state using the wide range of available quantum optical techniques. So far, however, quantum-coherent coupling of micromechanical oscillators has only been achieved using microwave fields at millikelvin temperatures. Optical experiments have not attained this regime owing to the large mechanical decoherence rates and the difficulty of overcoming optical dissipation. Here we achieve quantum-coherent coupling between optical photons and a micromechanical oscillator. Simultaneously, coupling to the cold photon bath cools the mechanical oscillator to an average occupancy of 1.7?±?0.1 motional quanta. Excitation with weak classical light pulses reveals the exchange of energy between the optical light field and the micromechanical oscillator in the time domain at the level of less than one quantum on average. This optomechanical system establishes an efficient quantum interface between mechanical oscillators and optical photons, which can provide decoherence-free transport of quantum states through optical fibres. Our results offer a route towards the use of mechanical oscillators as quantum transducers or in microwave-to-optical quantum links.