Producing GHZ state of nitrogen-vacancy centers in cavity QED

Abstract

We propose a scheme to generate the GHZ state of nitrogen-vacancy centers coupled to a whispering-gallery mode cavity. The implemented evolution is independent of the cavity field state with the assistance of a strong classical field, and thus not sensitive to the thermal state of the cavity. Meanwhile, it is fast compared to the convectional dispersive interaction induced operation in a cavity-assisted system. The scheme is readily scalable to the multiqubit scenario.     

Hot ductility of wrought 90Cu–10Ni alloy

Abstract

The ductility of a wrought 90Cu–10Ni alloy was investigated by tensile testing over a range of temperatures and for materials of different initial grain sizes. Ductilities were found to vary in a complex manner with temperature and grain size, but at all temperatures above 650 K failure occurred by grain boundary cavitation; good ductilities were associated with either grain boundary migration or recrystallisation during deformation. The microstructures of the deformed specimens were studied using optical microscopy and scanning electron microscopy, and the orientation of cracked boundaries, with respect to the tensile axis, was studied. Analysis of the results indicates that over the temperature range studied more than one cavity growth mechanism was operating. The ductility is discussed in terms of the relationship between the cavity growth mechanisms and restoration processes.

MST/722     

Entanglement-induced population trapping by Schrödinger's cat

Abstract

We propose an experiment that is a variation of the Schrödinger's cat ′paradox' wherein the entanglement between a microscopic system and a macroscopic system is of primary interest. The experiment involves tunable entanglement and serves as a model for controllable decoherence in the context of cavity quantum electrodynamics where atoms interact dispersively with a cavity field initially in a coherent state. The interaction produces an entanglement between the atom and the field, and the degree of entanglement can be probed by subjecting the atom to resonant classical radiation after it leaves the cavity. The amplitude of the resulting Rabi oscillations reflects the degree of the entanglement, there being no Rabi oscillations when the entanglement is maximum. We show that the cavity damping does not affect the experiment.     

Deterministic generation of a bit-stream of single-photon pulses

Abstract

We report a high efficiency scheme for generating a single-photon state transmitted out of an optical cavity. For realistic cavity QED parameters, we show that the scheme can produce a single-photon pulse with a probability exceeding 99% in a user-specified time interval. By recycling the system, the scheme can be used to create a bit-stream of single-photon pulses.     

Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract

A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.     

Plane strain fracture toughness of modern ferritic structural steels

Abstract

The temperature dependence of the plane strain fracture toughness of a low carbon, fine grain, ferritic steel for structural applications is investigated. The ductile–brittle transition is found to occur in the interval between 160 and 184 K. The experimental results are interpreted by an analytical model which permits calculation of the plane strain fracture toughness K _1c in the brittle domain as a function of the tensile properties and the cleavage fracture stress, making use of a piecewise approximation for the distribution of tensile stress on the crack axis and applying a deterministic fracture criterion at the stress peak. A similar criterion, which consists of equating the severest strain on the crack axis to a critical strain for cavity nucleation, provides the upper shelf fracture toughness. A relatively simple figure for predicting the transition temperature of steels in this family as a function of material properties can be obtained in this way.     

High power single mode output CO2 laser

Abstract

While attempting to reach TEMoo single mode high output power, the transverse discharge method was adopted. The optic axis, the direction of glow discharge and gas flow velocity are all mutually orthogonal. The discharge region has a 2.3 liter medium volume, and 100 m/sec gas flow. This small signal gain exceeds 0.8/m in the local region. We also adopted a stable multi‐path cavity for coordinating the larger volume laser medium. Under auxiliary discharge, the maximum output power can reach 1500W, at an efficiency of 9%.     

Crack growth in an orthotropic medium

Abstract

The elastostatic problem of an orthotropic body having a central inclined crack and subjected at infinity to a uniform biaxial load is considered. It is assumed that the crack line does not coincide with an axis of elastic symmetry of the body. The problem must be considered as one of general orthotropy, due in particular to the fact that the elastic coefficients of the material change with rotation of the reference system. The stress fields at the crack tip are reported and the presence of the non‐singular terms underlined. The Strain Energy Density Theory is extended to orthotropic materials. It is assumed that the Critical Strain Energy Density Factor has a polar variation. The crack initiation is determined via minimization of the ratio of the strain energy density over the material critical strain energy density, pointing out the effects of orthotropy and load biaxiality. The effects of the non‐singular terms on crack growth for different orthotropic materials is also studied, underling the relation between orthotropy and non‐singular terms.     

Bragg Cell Diffraction in Resonant Cavities

Abstract

Steier et al. [1] have shown that the diffraction efficiency of a stationary grating may be improved by placing the grating in a resonant cavity. In this paper we describe the diffraction of light by a Bragg cell in a resonant cavity. Large improvements in diffraction efficiency are shown to be possible if scattering losses on the surface of the cell can be kept small. The effects of introducing gain into the cavity are calculated and the changes in bandwidth, resolution and dynamic range are discussed for the system when used as a radiofrequency spectrum analyser. A multichannel fibre optic system has been designed and is described.     

Emission spectrum of a Λ-type three-level atom driven by the squeezed coherent field and grey-body radiation field

Abstract

By means of quantum electrodynamics, an analytical expression of emission spectrum for a Λ-type three-level atom with the two non-degenerate lower levels in the cavity is given. The character of the emission spectrum for the input in pure number state, a squeezed coherent state and grey-body state are exhibited. The effects of the atomic initial state, the field property, the cavity absorptivity and the system temperature on the time-dependent physical spectrum are analysed.     

Fock states generation in a kicked cavity with a nonlinear medium

Abstract

We discuss a model of a cavity filled with a passive nonlinear ?Kerr‘ medium and periodically kicked by a series of ultra-short laser pulses. The nonlinear medium is described by the (2q ? 1)th nonlinearity X ^(2q?1). We find analytical formulas describing the field states inside the cavity. We show that such a system can produce, depending on the order of the nonlinearity, superpositions of several Fock states with the small photon numbers (0,1; 0,1,2; etc). In particular, the one-photon state can be approached during the evolution of the system with X ⁽³⁾ nonlinearity provided the cavity losses are negligible. The purity of states generated in this process, however, can be seriously degraded by the cavity damping. We perform numerical calculations to validate our analytical results.     

Quick non-graphical method for deducing slip systems in cubic close packed metals in tension or compression

Abstract

A simple method is presented by which the operative slip system in a single crystal of a cubic close packed metal may be deduced by inspection from the indices of the tensile axis. The method has advantages over the commonly used graphical method, since it does not involve use of the stereogram.

MST/1990     

Pulsed single-mode laser in four-arm grazing incidence cavity

Abstract

A four-arm grazing-incidence cavity (GIC) is demonstrated. It ensures stable single-mode operation in a pulsed-laser system by interferometrically enhancing mode selection; the corresponding standard GIC operates on five modes. We compare the four-arm GIC with the standard GIC and with two other multiple-arm GICs and show that it gives the best overall performance in terms of mode selectivity and threshold. An analysis has been developed that allows cavity parameters to be optimized for mode selection. The analysis has been verified experimentally.     

Intensity noise reduction of twin beams by a passive semiconductor medium

Abstract

A passive optical system is proposed to explore the intensity quantum correlation of two twin beams to reduce the photon noise of one of them. It consists of using a semiconductor medium inside an optical cavity, which behaves as a nonlinear medium presenting a crossed Kerr effect. The intensity fluctuations of one beam modify the resonance condition of the cavity for the other beam and therefore its intensity. The medium is described microscopically within the two-level atom model. It is shown that, under typical experimental conditions, this system may produce noise reduction.     

Diffractive optical elements for intra-cavity beam-shaping of laser modes

Abstract

Diffractive optical elements (DOE) are applied as intra-cavity mode selection devices for customizing the fundamental mode of laser resonators for high power laser systems. Using a phase-conjugating mode selecting element (MSE) in a laser oscillator, we are able to produce a good approximation to a super-Gaussian mode with a near flat intensity profile. This offers higher energy extraction from any following laser amplifiers compared to an unmodified Gaussian TEM₀₀ mode. Two different designs for operation in a 1 m cavity length Nd:YAG master oscillator are presented. Both designs are surface relief phase elements fabricated in fused silica using photolithography with reactive-ion etching to produce 16 level elements for use in transmission. One element is designed to replace the cavity end mirror, while the other stands off an arbitrary distance from the end mirror. A novel iterated design for these transmissive elements is introduced. Numerical results and experimental measurements are presented and discussed.     

Stability of a laser cavity with a two-mirror multipass system

An investigation is made of the stability of a laser cavity in which one of the nontransmitting mirrors is a multipass system consisting of two spherical mirrors. The stability of the cavity depends strongly on the number of passes of the beam in the multipass system, the configuration of the mirrors, and the constriction of the beam entering the system. A stable cavity configuration ensures low diffraction losses in the system and efficient lasing. Pis’ma Zh. Tekh. Fiz. 25, 33–38 (November 12, 1999)     

Cavity QED analog of spin

Abstract

Using the even and odd coherent states, we show that a single mode cavity field, prepared in a coherent state by a classical source and manipulated by both dispersive and resonant interactions with atoms, is analogous to a spin one-half particle interacting with Stern–Gerlach magnets where the parity of the field is the analog of spin. Because the number of photons in the cavity may be large, the system we describe can exhibit quantum effects on at least a mesoscopic scale. We show that entangled two and three cavity systems can be generated. The three cavity case can be used to demonstrate the contradiction between local realistic theories and quantum mechanics in the manner proposed by Greenberger, Horne and Zeilinger in 1989 [13].     

Diffractive optical element used in an external feedback configuration to tune the wavelength of uncoated Fabry-Pérot diode lasers

Abstract

A diffractive optical element (DOE) has been designed, fabricated and used in an external feedback configuration to set the wavelength of operation of uncoated Fabry-Pérot diode lasers. The DOE was designed to replace the conventional elements of an external feedback system, which are a collimating lens and grating in the Littrow configuration. The goal was to simplify use of the external cavity laser by replacing the lens and grating with a single optical element while maintaining the performance that is achieved with a grating and lens. Four DOEs were fabricated with two different focal lengths and two different reflectivities. DOE external cavity lasers were tested for maximum tunable range and stability of the wavelength of operation and compared with an external cavity laser based on a lens and grating in the Littrow configuration. A 40 nm tuning range was achieved with the DOE external cavity laser and this is comparable with the tuning range of the external cavity lasers based on a grating and collimating lens in the Littrow configuration.     

N-level Atom Interacting with Single-mode Radiation Field: An Exactly Solvable Model with Multiphoton Transitions and Intensity-dependent Coupling

Abstract

We study the dynamics of an N-level atom coupled in a lossless cavity to a single-mode near-resonant quantized field. The atomic levels are coupled by the multiphoton transitions and the coupling constants between the field and the atomic levels are supposed to be intensity dependent. We find the exact solution for the state vector describing the dynamics of the atom-plus-field system. As an illustration we use the model for studying (i) the time evolution of the atomic occupation probability with the initially coherent field and (ii) the light squeezing, when the cavity field is initially in the vacuum state and the atom is prepared in the atomic ‘coherent state’ (a superposition of atomic states).     

Mode Interactions in Four-frequency Degeneracy-lifted Ring Lasers

Abstract

A non-planar ring cavity, with a non-reciprocal bias in the form of the longitudinal Zeeman effect on the gain medium, has been used to demonstrate four-mode bidirectional operation in a He-Ne ring laser at 632·8 nm. It has also been shown that this ring system is sensitive to rotation.