Generation of a superposition of odd photon number states for quantum information networks

We report on the experimental observation of quantum-network-compatible light described by a nonpositive Wigner function. The state is generated by photon subtraction from a squeezed vacuum state produced by a continuous wave optical parametric amplifier. Ideally, the state is a coherent superposition of odd photon number states, closely resembling a superposition of weak coherent states |alpha > - |-alpha >. In the limit of low squeezing the state is basically a single photon state. Light is generated with about 10,000 and more events per second in a nearly perfect spatial mode with a Fourier-limited frequency bandwidth which matches well atomic quantum memory requirements. The generated state of light is an excellent input state for testing quantum memories, quantum repeaters, and linear optics quantum computers.     

任意两个相干态的叠加态的相位分布和Wigner函数

从相位分布和Wigner函数两个方面研究了任意两个相干态|β〉 and |mβeiδ〉的叠加态的量子统计性质.结果表明这种叠加态的非经典特性与β2,振幅系数m,相干态间的位相差δ以及叠加系数间的位相差都有关.当参量选择合适,这种叠加态存在着量子效应.计算了两个相干态等几率混合系综的相位分布和Wigner函数,经过与前者比较,结果表明由于相干项的存在,使得叠加态具有很好的量子力学行为.     

任意两个相干态的叠加态的相位分布和Wigner函数(英文)

从相位分布和Wigner函数两个方面研究了任意两个相干态|β〉and |mβeiδ〉的叠加态的量子统计性质.结果表明这种叠加态的非经典特性与β2,振幅系数m,相干态间的位相差δ以及叠加系数间的位相差都有关.当参量选择合适,这种叠加态存在着量子效应.计算了两个相干态等几率混合系综的相位分布和Wigner函数,经过与前者比较,结果表明由于相干项的存在,使得叠加态具有很好的量子力学行为.     

Influence of Intrinsic Decoherence in the Presence of Stark Shift on Nonclassical Properties of the Two-Mode JCM

We study the influence of intrinsic decoherence in the presence of Stark shift for the two-mode Jaynes—Cummings model (JCM). An analytic solution of the Milburn equation for the multiquant two-mode JCM Hamiltonian is obtained. We use this solution to investigate the influence of intrinsic decoherence and Stark shift on nonclassical properties of the system, for the resonant and the off-resonant cases. We compare the behavior of the system in the case of having a coherent superposition state and a statistical mixture of coherent states as an initial field.     

Enhancement of feasibility of macroscopic quantum superposition state with the quantum Rabi-Stark model

We propose an efficient scheme to generate a macroscopical quantum superposition state with a cavity optomechanical system, which is composed of a quantum Rabi-Stark model coupling to a mechanical oscillator. In a low-energy subspace of the Rabi-Stark model, the dressed states and then the effective Hamiltonian of the system are given. Due to the coupling of the mechanical oscillator and the atom-cavity system, if the initial state of the atom-cavity system is one of the dressed states, the mechanical oscillator will evolve into a corresponding coherent state. Thus, if the initial state of the atom-cavity system is a superposition of two dressed states, a coherent state superposition of the mechanical oscillator can be generated. The quantum coherence and their distinguishable properties of the two coherent states are exhibited by Wigner distribution. We show that the Stark term can enhance significantly the feasibility and quantum coherence of the generated macroscopic quantum superposition state of the oscillator.     

Production of the Superposition of Nonlinear Coherent States and Entangled Nonlinear Coherent States

In this paper, by using the parity operator as well as the nonlinear displacement-type operator, we define new operators which by the action of them on the vacuum state of the radiation field, superposition of two nonlinear coherent states and two-mode entangled nonlinear coherent states are generated. Also, we show that via the generalization of the presented method, the superposition of more than two nonlinear coherent states and n-mode entangled nonlinear coherent states can be generated.     

The dynamics of a THz Rydberg wavepacket

An optically excited Rydberg wavepacket can be generated by exciting the electron from a low-lying state to a coherent superposition of high-lying states with a short broadband optical pulse. A special kind of Rydberg wavepacket is generated in the case of a interaction of a weak THz half cycle pulse with a stationary Rydberg state, called the THz wavepacket. This THz wavepacket is a coherent superposition of the initial Rydberg state and its neighbouring states. We have investigated the time evolution of THz wavepackets by measuring the impact of two in time delayed half cycle pulses ( ≈ 200 V cm^-1) on the population of a stationary (n = 40) Rydberg state in rubidium. The first half cycle pulse creates the THz wavepacket and the second half cycle pulse probes the dynamics of the THz wavepacket. We support our experimental data by numerically solving the Schr?dinger equation and with a semi-classical picture. Whereas an optically excited wavepacket is initially localized, a THz wavepacket is initially delocalized and becomes localized after half a revival time. Received 23 August 2000 and Received in final form 27 March 2001     

Production of the Superposition of Nonlinear Coherent States and Entangled Nonlinear Coherent States

In this paper, by using the parity operator as well as the nonlinear displacement-type operator, we define new operators which by the action of them on the vacuum state of the radiation field, superposition of two nonlinear coherent states and two-mode entangled nonlinear coherent states are generated. Also, we show that via the generalization of the presented method, the superposition of more than two nonlinear coherent states and n-mode entangled nonlinear coherent states can be generated.     

Generating a Four-qubit Photon-Number Cluster State via Cross-Kerr Medium

A scheme is proposed for generating a photon-number entangled cluster state among four modes. The scheme only uses Kerr medium and homodyne measurement on probe coherent light fields, which can be efficiently made in quantum optical laboratories. The photon in the signal mode is prepared in a superposition state of the vacuum state and one-photon state while the probe beam is initially set in a intense coherent state superposition. It is shown that under certain conditions, the four-photon cluster state can be generated effectively with high success probability and homodyne detection required only once, and the scheme is feasible by current experimental technology.     

Dynamic statistical properties of squeezed coherent state superpositions

We carried out a study of statistical properties of a squeezed coherent state superposition (SCSS) evolving under a thermal reservoir at zero and finite temperature. Our results reveal some peculiarities not noticed by previous studies, which were mainly focused on ideal (lossless) properties of SCSS. Our main results indicate the existence of realistic parameters for which SCSS, at zero absolute, remains sub-Poissonian or squeezed asymptotically, while, at finite temperature, we found that SCSS only loses its squeezing or sub-Poissonian character at large times as compared with the time needed to the SCSS become a complete mixture.     

双Λ型原子系统中制备相干叠加态的研究(英文)

本文讨论了在双Λ型原子系统中制备相干叠加态的方法:一个Λ型系统通过控制激光而另一个Λ型系统采用部分受激拉曼绝热通道的方法.在理论上分析了产生任意相干叠加态的可能性并且讨论了透热系统在产生相干叠加态过程中的重要性.研究表明,没有透热过程是不可能制备出任意的叠加态.应用数值方法验证理论分析是正确,并且指出任意叠加态的产生只与控制脉冲的时间延迟有关.     

Creation and measurement of a coherent superposition of quantum states

We demonstrate experimental techniques for creating and measuring a coherent superposition of two degenerate atomic states with equal amplitudes in metastable neon. Starting from state (3)P(0), we create adiabatically a coherent superposition of the magnetic sublevels M=+/-1 of the state (3)P(2) using a tripod stimulated Raman adiabatic passage scheme. The measurement is based on the coupling of the levels (3)P(2)<-->(3)P(1) by a linearly polarized laser, followed by the detection of the population in the (3)P(2)(M=+/-2) states as a function of the polarization angle of that laser.     

叠加激发对相干态的非经典特性

从激发对相干态出发,构造了叠加激发对相干态,研究了该叠加态的非经典特性.结果表明:在一定条件下,随着相位的变化,叠加态场模的平均光子数呈现类似于拉比振荡的坍塌与复原现象,与激发对相干态相比,在叠加激发对相干态中亚泊松光子统计特性和CauchySchwatz不等式的破坏都得到了增强,但正交相位分量的压缩减弱.     

A New Superposition of Two Coherent States and its Quantum Properties

We investigate a new superposition of two coherent states via conditional measurement on a Mach-Zehnder interferometer (MZI). The resulted output state is obtained by using the superposition of two opposite coherent states with the arbitrary relative phase factors for the a-mode and vacuum state in the b-mode. It is shown that the angle of the phase shifter between the two arms of the MZI is a very important parameter in this new state.

     

The Wigner function and phase properties of superposition of two coherent states with the vacuum state

This paper discusses some statistical properties of the superposition of two coherent states with a vacuum state, such as sub-Poissonian photon statistics and negativity of the Wigner function. Phase probability distribution and phase variance are calculated. Special cases of the constructed superposition states are presented. The results show that depending on the vacuum state coefficient γ and the coherent state coefficient α, it can generate a variety of nonclassical states.     

一种制备四光子相干态的新方案

本文提出了一种利用原子-腔场之间的Raman相会作用来制备四光子相干态的新方案.同样,还可以利用该方法制备八成分迭加态.     

叠加的奇偶SU(1,1)相干态的统计性质

研究了将两个SU(1,1)相干态｜ζ,k〉和｜ζ,k〉叠加起来得到的新的量子态的统计性质．偶SU(1,1)相干态｜ζ,1/4〉和奇SU(1,1)相干态｜ζ,3/4〉分别对应于压缩真空态和压缩单光子数态．适当选取SU(1,1)态的相位角和叠加时的相对相位,得到的新的量子态比单个SU(1,1)相干态表现出大大增强的正交分量压缩和光子反群聚效应．也说明了怎样准备这样的叠加态． 关键词：     

Generation of generalized coherent states with two coupled Bose-Einstein condensates

We present a scheme to prepare generalized coherent states in a system with two species of Bose-Einstein condensates. First, within the two-mode approximation, we demonstrate that a Schrödinger cat-like state can be dynamically generated and, by controlling the Josephson-like coupling strength, the number of coherent states in the superposition can be varied. Later, we analyze numerically the dynamics of the whole system when interspecies collisions are inhibited. Variables such as fractional population, Mandel parameter and variances of annihilation and number operators are used to show that the evolved state is entangled and exhibits sub-Poisson statistics.     

Engineering of Two Quantum States via Conditional Measurement on Two-Mode Squeezed State

We propose a scheme for the simultaneously preparation radiation-field modes of a single photon and a superposition of zero- and one-photon states, based on the coherent quantum state displacement and photon subtraction from two-mode squeezed state. It is shown that the single-photon and the superposition states can be obtained by only choosing the suitable parameter of displacements. The experimental feasibility to accomplish this scheme is also discussed.     

A Simple Method on Generating any Bi-Photon Superposition State with Linear Optics

We present a simple method on the generation of any bi-photon superposition state using only linear optics.In this scheme, the input states, a two-mode squeezed state and a bi-photon state, meet on a beam-splitter and the output states are post-selected with two threshold single-photon detectors. We carry out corresponding numerical simulations by accounting for practical experimental conditions, calculating both the Wigner function and the state fidelity of those generated bi-photon superposition states. Our simulation results demonstrate that not only distinct nonclassical characteristics but also very high state fidelities can be achieved even under imperfect experimental conditions.