Enhancement and generation of sum squeezing in two-mode light in mixing with coherent light using a beam splitter

Recently, we showed [J. Phys. B: At. Mol. Opt. Phys. 38, 665 (2005)] that the `amplitude-squared squeezing', a non-classical feature, can be enhanced in mixing with a coherent light beam using a beam splitter. Here, we show that the sum squeezing in a two-uncorrelated-mode light beam (one mode is in Gaussian state and the other one is in coherent state), which is degenerate limit of amplitude-squared squeezing, may be generated or enhanced in mixing with a two-mode coherent light beam using a beam splitter.     

Photon number distributions of output fields from a beam splitter

We examined the photon statistics of the output light field of a lossless symmetric beam splitter when a n-photon occupation number state and an arbitrary light field are present on the two input ports of the beam splitter. We showed that both the wave-like nature and the particle-like nature of light are contributed to the photon number distribution by investigation of the difference photon number probability at the output port.     

Controlled Quantum Teleportation of Superposed Coherent State Using GHZ Entangled Coherent State

Controlled quantum teleportation of superposed coherent states using GHZ entangled 3-mode coherent states is studied. Proposed scheme can be implemented experimentally using linear optical components such as a symmetric lossless beam splitter, two phase-shifters and two photon counters. Fidelity is found close to unity for appreciable mean number of photons in coherent states and is 0.99 for mean photon number equal to two.

     

Engineering Two-Mode Non-Gaussian States with Vortex Structures Using a Beam Splitter

Vortex structure and entanglement properties of output field from a beam splitter are investigated. With a n-photon Fock state and a coherent state as the inputs, it is found that the output state before a beam splitter bears a vortex structure in quadrature space and is always entangled and non-classical based on the linear entropy criterion and the P-function analysis in phase space.     

Optimization of recording process in laser irradiance modulated time-average holography of sinusoidally vibrating objects

The beam ratio during modulation of laser irradiance in time-average hologram interferometry of a sinusoidally vibrating object, is discussed for retaining the exposure time, and reducing it if the normal brightness of the higher order J₀ fringes is tolerable. It is assumed that a variable ratio lossless beam splitter is used for the beam division process.     

A quantum description of the beam splitter

We derive the unitary transformation that embodies the action of a lossless plane-parallel beam splitter on an incident light beam. We use the transformation to illustrate with some examples how fluctuations and noise in one light mode may get coupled with those in another mode.     

Splitting four ensembles of two-qubit quantum information via three Einstein-Podolsky-Rosen pairs

Enlightened by Zhang and Cheung’s original idea [J. Phys. B 41, 015503 (2008)], we put forward a novel tripartite quantum information splitting scheme by using three Einstein-Podolsky-Rosen pairs as quantum channels. Our scheme is applicable for perfectly splitting four ensembles of quantum information known by the splitter in priori. In contrast to the general scheme using the same quantum channels [Eur. Phys. J. D 39, 459 (2006)], our scheme has distinct advantages in quantum resource consumption, quantum operation intensity, classical communication cost and efficiency when dealing with the four specific ensembles of quantum information.     

Compensation of beam walk-off in hollow metal waveguides

Hollow metal waveguides feature well collimated beams and small losses across air gaps. This enables introduction of multiple optical beam splitters, or taps, along the waveguide to multicast signals from a source to multiple receivers. The splitters need to be of sufficient thickness to provide mechanical integrity and ease of handling. As a result, passing through the thickness leads to a beam walk-off. Walk-off dependence on the splitter thickness and its effect on the system optical efficiency are investigated. Two methods to compensate the walk-off are described: by offsetting the outgoing waveguide, and by introducing an additional symmetric optical element to shift the beam back to the original optical path. Both methods have been shown to effectively mitigate the walk-off effects.     

Violation of Bell's inequality with photons from independent sources

We report a violation of Bell's inequality using one photon from a parametric down-conversion source and a second photon from an attenuated laser beam. The two photons were entangled at a beam splitter using the postselection technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]]. A quantum interference pattern with a visibility of 91% was obtained using the photons from these independent sources, as compared with a visibility of 99.4% using two photons from a central parametric down-conversion source.     

Optical transformer of photon statistics

The possibility of a linear optical transformer of photon statistics for multimode light is suggested. The transformation coefficients are obtained explicitly in terms of multivariable Hermite polynomials. As physical examples of a linear transformer a resonator with moving walls and a lossless beam splitter are discussed as optical elements that change the photon statistics of light beams. The beam splitter is shown to produce redistribution of quadrature squeezing and correlation between two modes of light.     

Optimization of exposure time in linear hologram recording by pre-exposure or post-exposure

Using a given intensity of the laser beam, the optimum hologram recording time is discussed when the recording is performed on a pre-exposed or post-exposed medium, retaining the reconstruction efficiency the same as that in the corresponding conventional recording. It is assumed that a variable ratio, lossless beam splitter is used for the beam division process.     

Quantum disentanglement and phase measurements

A 5050 beam splitter disentangles a two-mode squeezed vacuum state into two single-mode squeezed vacuum states. With the proper choice of parameters these two single-mode states will be identical. If one is passed through a device which shifts its phase, then the phases of the shifted and reference (unshifted) modes can be determined by the Vogel-Schleich technique [Phys. Rev. A44 (1991) 7642]. In this way the phase difference, i.e. the phase shift, can be measured to an accuracy of 1/N, whereN is the total number of photons coming into the beam splitter. We also propose an improved scheme involving the disentanglement of a shifted two-mode squeezed vacuum state. This leads to two shifted squeezed vacaum states at the output of the beam splitter. If one of these is passed through the phase shifter, then by performing homodyne measurements on the shifted and unshifted modes the phase shift can again be determined to an accuracy of 1/N.This research was supported by the National Science Foundation under grants INT-9221716 and PHY-9201912.     

Quantum interference of ultrastable twin optical beams

We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam splitter to convert number-difference squeezing into phase-difference squeezing, and thus provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.     

Quantum-enhanced interferometry with asymmetric beam splitters

In this paper,we investigate the phase sensitivities in two-path optical interferometry with asymmetric beam splitters.Here,we present the optimal conditions for the transmission ratio and the phase of the beam splitter to gain the highest sensitivities for a general class of non-classical states with parity symmetry.Additionally,we address the controversial question of whether the scheme with a combination of coherent state and photon-added or photon-subtracted squeezed vacuum state is better or worse than the most celebrated one using a combination of coherent state and squeezed vacuum state.     

Interference of two photons of different color

We consider the interference of two photons with different colors in the context of a Hong-Ou-Mandel experiment, in which single photons enter each of the input ports of a beam splitter, and exit together in the same, albeit undetermined, output port. Such interference is possible if one uses an active (energy-non-conserving) beam splitter. We find scenarios in which one “red” and one “blue” photon enter the beam splitter, and either two red or two blue photons exit, but never one of each color. We show how the precise form of the active beam-splitter transformation determines in what way the spectral degrees of freedom of the input photons should be related to each other for perfect destructive interference of the different-color components in the output. We discuss two examples of active beam splitters: one is a gedanken experiment involving a moving mirror and the other is a more realistic example involving four-wave mixing in an optical fiber.     

Beam delivery system with a non-digitized diffractive beam splitter for laser-drilling of silicon

We report a beam-delivery system consisting of a non-digitized diffractive beam splitter and a Fourier transform lens. The system is applied to the deep-drilling of silicon using a nanosecond pulse laser in the manufacture of inkjet printer heads. In this process, a circularly polarized pulse beam is divided into an array of uniform beams, which are then delivered precisely to the process points. To meet these requirements, the splitter was designed to be polarization-independent with an efficiency>95%. The optical elements were assembled so as to allow the fine tuning of the effective overall focal length by adjusting the wavefront curvature of the beam. Using the system, a beam alignment accuracy of<5 μm was achieved for a 12-mm-wide beam array and the throughput was substantially improved (10,000 points on a silicon wafer drilled in ~1 min). This beam-delivery scheme works for a variety of laser applications that require parallel processing.     

Higher diffraction order photorefractive optical beam splitter

A higher diffraction order photorefractive (PR) optical beam splitter has been realized based on a PR higher diffraction order grating. In the experiments, the beam splitter was produced by two-wave coupling at a small incident angle in Fe:LiNbO₃ using the output from a He–Ne laser at 632.8 nm. An incident signal beam containing three different wavelengths (632.8, 532.0 and 488.0 nm) was split into multi-output beams by the beam splitter. The size of higher diffraction order is given and the influence of crystal thickness is discussed. Results show that the higher diffraction order PR optical beam splitter provides a practical method to split a multi-wavelength signal beam.     

Generation and classification of robust remote symmetric Dicke states

In this paper, we present an approach to generating arbitrary symmetric Dicke states with distant trapped ions and linear optics. Distant trapped ions can be prepared in the symmetric Dicke states by using two photon-number-resolving detectors and a polarization beam splitter. The atomic symmetric Dicke states are robust against decoherence, for atoms are in a metastable level. We discuss the experimental feasibility of our scheme with current technology. Finally, we discuss the classification of arbitrary n-qubit symmetric Dicke states under statistical local operation and classical communication and prove the existence of [n/2] inequivalent classes of genuine entanglement of n-qubit symmetric Dicke states.     

纠缠压缩真空态的纠缠转移

通过分析光学分束器对压缩真空态光场的作用,发现如果分束器的输入光是两束具有同样振幅和相位的单模压缩真空态光场,则输出光为双模压缩真空态光场;若分束器的输入光是两束具有同样振幅但有π相位差的单模压缩真空态光场,则输出光仍为两束单模压缩真空态光场.对于双模压缩真空态光场,每个模中容纳的光子数可以是基数或偶数.而对于单模压缩真空态光场,每个模中只能包含偶数个光子.根据这些结果,提出了一个纠缠转移的方案.在这个方案中,两个纠缠压缩真空态光场被用作量子信道,通过利用光学分束器作用和光子数探测的方法,并在经典通讯的帮助下,实现了三个通讯伙伴之间的纠缠转移.     

Realization of Hardy's thought experiment with photons

We present an experimental realization of Hardy's thought experiment [Phys. Rev. Lett. 68, 2981 (1992)], using photons. The experiment consists of a pair of Mach-Zehnder interferometers that interact through photon bunching at a beam splitter. A striking contradiction is created between the predictions of quantum mechanics and local hidden variables. The contradiction relies on nonmaximally entangled position states of two particles. A Clauser-Horne-type inequality is derived and violated.