Quantum teleportation of optical images with frequency conversion

A new version of quantum teleportation of optical images in continuous variables is considered. The new scheme is based on quantum entanglement in continuous variables between light fields of different frequencies and allows wavelength conversion between input and teleported images. The protocol of quantum teleportation with frequency conversion can be used as a combined part of light/matter interface in quantum parallel data processing and in a parallel quantum memory.     

Quantum teleportation of optical quantum gates

We show that a universal set of gates for quantum computation with optics can be quantum teleported through the use of EPR entangled states, homodyne detection, and linear optics and squeezing operations conditioned on measurement outcomes. This scheme may be used for fault-tolerant quantum computation in any optical scheme (qubit or continuous-variable). The teleportation of nondeterministic nonlinear gates employed in linear optics quantum computation is discussed.     

Quantum teleportation

Quantum Teleportation of one qubit of information using entangled state of two qubit is explained. It is shown that if quantum state of N qubits is to be teleported, the requirement is entangled state of at least 2N qubits. A scheme of teleportation of a superposition of even and odd coherent states was suggested by Van Enk and Hirota for teleportation of superposed coherent state, success of which is ? according to the authors. It is shown how this scheme can be modified so as to make the success nearly 1. It is also explained how decoherence can be taken into account and how such schemas can be applied to similar phenomena of entanglement diversion and entanglement swapping.     

Quantum information processing in optical images

Optical images can be used to transport, store and process information in a parallel way. We discuss different results obtained in the domain of ‘quantum imaging’, aiming at exploiting at the same time the quantum properties of optical images and their intrinsic parallelism. We define the notion of standard quantum limit (SQL) in optical resolution, set by the quantum noise of usual coherent light, and show that it can be much lower than the diffraction limit. We also prove that this limit can be circumvented by especially designed nonclassical and multimode light. We present an experiment showing that OPOs oscillating inside an exactly confocal cavity actually produce such transverse multimode nonclassical light. We finally describe another experiment which has surpassed the SQL in the case of beam positioning, both in the 1D and 2D cases.     

Quantum fluctuations of a vortex in an optical lattice

Using a variational ansatz for the wave function of the Bose-Einstein condensate, we develop a quantum theory of vortices and quadrupole modes in a one-dimensional optical lattice. We study the coupling between the quadrupole modes and Kelvin modes, which turns out to be formally analogous to the theory of parametric processes in quantum optics. This leads to the possibility of squeezing vortices. We solve the quantum multimode problem for the Kelvin modes and quadrupole modes numerically and find properties that cannot be explained with a simple linear-response theory.     

Polymer-dispersed liquid crystal films for storing optical holographic images

We have developed an economic liquid crystal-polymer dispersion material that can be used for storing optical holographic images. In this paper, we demonstrate the use of thin samples of this material for such an application. The obtained results show that the written gratings-holograms are permanent, but are electrically switchable. Furthermore, the diffraction efficiency is high and does not change significantly after many tests over a period of months. Thus, we believe this material is promising for practical uses.     

Quantum images in non degenerate optical parametric oscillators

Quantum images, that is inhomogeneous field distributions purely generated by quantum fluctuations, persist when passing from the degenerate to the non-degenerate case of optical parametric oscillators (OPO). Below the threshold for parametric oscillation where the near-field distributions are homogeneous both in intensity and phase, appropriate spatial correlation functions anticipate the transverse spatial pattern that appears above threshold. In particular, the angular dependence of the far field spatial correlation function is able to reveal the travelling-wave nature of the phase pattern above threshold typical of nondegenerate OPOs. Cross-correlation functions between signal and idler intensities show clear evidence of the non-classical nature of the output light. Received 8 October 1999     

Quantum teleportation of particles in an environment

We discuss the teleportation of particles in an environment of an N-body system. In this case, we can change a many-body system into an arbitrary shape in space by teleporting some or all the constituent particles, and thus we call the quantum teleportation under this circumstance as quantum tele-transformation(QTT). The particular feature of QTT is that the wave function of the internal degrees of freedom remains the same, while the spatial wave function experiences a drastic change. The notion of QTT provides conceptual and pedagogical convenience for quantum information processing.In view of QTT, teleportation is the change of a single particle in space, while entanglement swapping is the change of one particle of an entangled pair.     

Quantum teleportation and Kerr-Newman spacetime

We consider the teleportation in the background of Kerr-Newman spacetime. Because of the Hawking effect, the fidelity of the teleportation is reduced. The results also show the fidelity is closely related to the mass, charge and rotating velocity of the black hole: high fidelity can be reached for massive, slowly rotating Kerr-Newman black holes.     

Quantum fluctuations of superfluorescence delay observed with ultrashort optical excitations

We present an observation of fluctuations in delay times of the yoked-superfluorescence pulses generated in atomic rubidium. The yoked-superfluorescence was induced through two-photon excitation of cascade transitions by ultrashort (∼100 fs) laser pulses. A statistical distribution and fluctuations of delay times were studied as the pump pulse energy varied, effectively changing the number of participating atoms. The standard deviation in the delay-time statistics decreases when the pump power increases. The experimental data support the theoretical model of the quantum fluctuations of superfluorescence.     

Quantum properties of optical images in coupled nondegenerate parametric processes

Quantum properties of parametric amplification and frequency conversion of an optical image in coupled parametric interactions are analyzed for the case of a remote object. The coupled-wave interaction consists of a traditional process of parametric amplification in the high-frequency pump field accompanied by the frequency mixing of generated and pump waves. The photon number density and signal-to-noise ratio at the interacting frequencies are studied in the image plane at the output of the nonlinear frequency converter in the fixed pump field approximation. The degree of entanglement of optical images at frequencies above and below the pump frequency is investigated.     

变分法研究一维Bose-Fermi系统的稳定性

利用能量泛函变分法研究了一维Bose-Fermi系统稳定基态的存在条件.根据Bose-Fermi系统的Lagrange量可以得到三维Bose-Fermi体系所满足的非线性动力学方程组.当外势阱的横向囚禁频率远大于轴向囚禁频率时,体系可以当作一维模型来处理.从描述三维体系的动力学方程可以得到描述一维体系的动力学方程,选取适当的无量纲参数,可以对一维动力学方程组进行无量纲处理,得到数值计算和理论分析中常用到的无量纲方程.选择高斯型试探解(简单孤立子解),利用能量泛函变分法得到一维Bose-Fermi体系稳定的 关键词： Bose-Fermi 稳定性 基态 临界条件     

Quantum teleportation with a three-Bell-state analyzer

We present a novel Bell-state analyzer (BSA) for time-bin qubits allowing the detection of three out of four Bell states with linear optics, two detectors, and no auxiliary photons. The theoretical success rate of this scheme is 50%. Our new BSA demonstrates the power of generalized quantum measurements, known as positive operator valued measurements. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a fidelity larger than the cloning limit.     

Quantum logic networks for probabilistic teleportation

By eans of the primitive operations consisting of single-qubit gates.two-qubit controlled-not gates,Von Neuman measurement and classically controlled operations.,we construct efficient quantum logic networks for implementing probabilistic teleportation of a single qubit,a two-particle entangled state,and an N-particle entanglement.Based on the quantum networks,we show that after the partially entangled states are concentrated into maximal entanglement,the above three kinds of probabilistic teleportation are the same as the standard teleportation using the corresponding maximally entangled states as the quantum channels.     

Quantum teleportation of a single-photon wave packet

A quantum teleportation scheme based on the EPR-pair entangled with respect to the “energy+time” variables is proposed. Teleportation of the multimode state of a single-photon wave packet is considered.     

Quantum teleportation of entangled squeezed vacuum states

An optical scheme for probabilistic teleporting entangled squeezed vacuum states (SVS) is proposed. In this scheme, the teieported state is a bipartite entangled SVS, and the quantum channel is a tripartite entangled SVS. The process of the teleportation is achieved by using a 50/50 symmetric beamsplitter and photon detectors with the help of classical information.     

Quantum processing of images by continuous wave optical parametric amplification

We have experimentally shown that a degenerate optical parametric oscillator pumped by a cw laser, inserted in a cavity having degenerate transverse modes such as a hemiconfocal or confocal cavity, and operating below the oscillation threshold in the regime of phase sensitive amplification, is able to process input images of various shapes in the quantum regime. More precisely, when deamplified, the image is amplitude squeezed; when amplified, its two polarization components are intensity correlated at the quantum level. In addition, the amplification process of the images is shown to take place in the noiseless regime.     

Quantum limits in the measurement of very small displacements in optical images

We consider the problem of the measurement of very small displacements in the transverse plane of an optical image with a split photodetector. We show that the standard quantum limit for such a measurement, which is equal to the diffraction limit divided by the square root of the number of photons used in the measurement, cannot be overcome by use of ordinary single-mode squeezed light. We give the form of possible multimode nonclassical states of light, enabling us to enhance by orders of magnitude the resolution of such a measurement beyond the standard quantum limit.     

基于量子隐形传态的量子保密通信方案

量子保密通信包括量子密钥分发、量子安全直接通信和量子秘密共享等主要形式.在量子密钥分发和秘密共享中,传输的是随机数而不是信息,要再经过一次经典通信才能完成信息的传输.在量子信道直接传输信息的量子通信形式是量子安全直接通信.基于量子隐形传态的量子通信(简称量子隐形传态通信)是否属于量子安全直接通信尚需解释.构造了一个量子隐形传态通信方案,给出了具体的操作步骤.与一般的量子隐形传态不同,量子隐形传态通信所传输的量子态是计算基矢态,大大简化了贝尔基测量和单粒子操作.分析结果表明,量子隐形传态通信等价于包含了全用型量子密钥分发和经典通信的复合过程,不是量子安全直接通信,其传输受到中间介质和距离的影响,所以不比量子密钥分发更有优势.将该方案与量子密钥分发、量子安全直接通信和经典一次性便笺密码方案进行对比,通过几个通信参数的比较给出各个方案的特点,还特别讨论了各方案在空间量子通信方面的特点.