Stimulated Raman Scattering of Squeezed Light with Pump Depletion

Abstract

Using the approximation of small fluctuations around a stationary point, photon statistics and squeezing of vacuum fluctuations are derived in stimulated Raman scattering including the coupling of photon-photon and photon-phonon modes. The depletion of pump light is described and it is shown that a regime of inversion of the process is related to an increase in quantum fluctuations, which are finally reduced again, more in the anti-Stokes mode than in the Stokes mode. If the anti-Stokes coupling is stronger than the Stokes coupling, then an oscillating behaviour of the statistical characteristics occurs and substantial squeezing can be found in photon-phonon modes.     

Non-classical Light in Nonlinear Symmetric and Asymmetric Couplers

Abstract

We derive the quantum-statistical properties of light beams in nonlinear symmetric and asymmetric couplers composed of linear waveguides and a nonlinear waveguide operating by the second-harmonic generation. This device can exhibit non-classical behaviour in single and compound modes and produce squeezed and/or sub-Poissonian light. Power solutions are obtained up to the twelfth order adopting a symbolic computer method. In addition, new higher-order results for the asymmetric coupler are presented.     

Scheme to measure quantum stokes parameters and their fluctuations and correlations

Abstract

We propose a scheme to measure quantum Stokes parameters, their fluctuations and correlations. The proposal involves measurements of intensities and intensity-intensity correlations for suitably defined modes, which can be produced by a combination of half-wave and quarter-wave plates.     

Forward and Backward Four-wave Mixing of Non-classical Light with Pump Depletion

Abstract

Photon statistics and non-classical behaviour of forward and backward four-wave mixing are examined including the coupling of modes in the approximation of small fluctuations around a stationary point, which is analytically determined and conditions for its stability are obtained. The depletion of pump modes is involved and effects of nonlinear dynamics, non-classical behaviour of input radiation, external noise and losses are included.     

Quantum phase measurements and non-classical polarization states of light

Abstract

In our paper we consider the non-classical behaviour of both the Hermitian (observable) Stokes parameters of light and the phase difference of two modes that describe the quantum polarization states of optical field. To characterize the degree of polarization of light we introduce a new quantity taking into account the quantum properties of different quantum states of two orthogonally polarized modes. The problem of determination of the phase difference in two modes of optical field for the quantum polarization states of light is discussed. To describe in general such a quantum field we introduce two pairs of the phase operators: the phase angles for the Stokes parameters of light in a three-dimensional picture of the Poincaré sphere. We also consider a special type of the eight-port polarization interferometer (polarimeter) for simultaneous homodyne detection of both the Stokes parameters of light and the polarization phase operators and their fluctuations as well. Using an anisotropic (spatioperiodic) Kerr-like nonlinear medium associated with the polarization interferometer we could generate and also observe the polarization-squeezed phase states of light. The fluctuations in the phase difference between two orthogonally polarized modes for these non-classical states are less than the fluctuations for light in coherent state.     

Non-classical behaviour and switching in Kerr nonlinear couplers

Abstract

Directional nonlinear couplers composed of two Kerr nonlinear waveguides are studied. Quantum consistent solutions of the equations of motion are obtained showing the collapses and revivals of the field mode amplitudes. The approximate method is also adopted for the contradirectional geometry and the switching accompanied by collapses of the modes is revealed. Kerr couplers with varying linear coefficients are examined and possible controls of the switching of modes, for instance, digital switching and fast switching are demonstrated. The two-mode squeezing of vacuum fluctuations and the generation of pure states are shown.     

Mode of drug binding to DNA determined by optical tweezers force spectroscopy

Abstract

Optical tweezers were employed to investigate the effects of small DNA-binding molecules on the low-force (≤ 15 pN) stretching behaviour of single DNA molecules. As the canonical B-DNA helix is not perturbed in this force regime, the effects on DNA elasticity observed upon drug binding provide useful insight into how DNA-binding drugs may alter in vivo processes. In this study, the effects of agents with different DNA binding modes were analysed. DNA force—extension curves were recorded in the presence of netropsin, a purely minor groove-binding antibiotic drug, ethidium bromide, an intercalating fluorescent dye, and berenil, an antiprotozoal drug proposed to exhibit both intercalative and minor groove-binding modes. Applying an approximation of the worm-like chain model, which describes the low-force stretching behaviour, the results were analysed in terms of the DNA contour length and persistence length. From these single molecule studies it was observed that minor groove-binding and intercalating modes of DNA-binding could be distinguished based on changes to DNA elasticity.     

SU(1, 1) and SU(2) Squeezing in Trilinear Optical Processes

Abstract

The squeezing properties in terms of SU(1, 1) and SU(2) operators for the case of trilinear processes are studied. The initial state of the system is supposed to be a coherent state in one of the modes and number states in the remaining modes. It is pointed out that in several cases a considerable amount of squeezing can be achieved. Due to the common mathematical structure the case of a two-mode coupler with intensity dependent coupling is also analysed.     

Investigation of potential and compositional fluctuations in CuGa3Se5 crystals using photoluminescence spectroscopy

We studied the photoluminescence (PL) properties of the ordered defect compound CuGa₃Se₅. Different single crystals were grown by the vertical Bridgman method and by the solid phase crystallization method. Their crystal structure and cell parameters were determined by X-ray diffraction. The PL spectra were recorded at T = 10-300 K. Also, laser power dependences were studied. We found an asymmetric PL band at 1.76 eV. PL band shifts towards higher energies with increasing laser power. The shape and properties of this band assure the presence of potential and compositional fluctuations. The influence of both fluctuations on the PL properties of CuGa₃Se₅ is studied and the radiative recombination processes are explained.     

The Influence of Phase-destroying and Absorption Processes on Squeezing

Abstract

The already well known sensitivity of genuine quantum effects to loss processes is investigated for squeezing. Owing to the phase dependence of its quantum fluctuations, a squeezed state is extraordinarily fragile with respect to phase-destroying processes. This sensitivity increases with increasing degree of squeezing. A present coherent photon number enhances this disturbing effect.     

Parametric oscillation with squeezed vacuum reservoirs

Employing the quantum Hamiltonian describing the interaction of a two-mode light (signal–idler modes) generated by a non-degenerate parametric oscillator (NDPO) with two uncorrelated squeezed vacuum reservoirs (USVR), we derive the master and the Fokker–Planck equations. The corresponding Fokker–Planck equation for the Q-function is then solved employing a propagator method developed by K. Fesseha [J. Math. Phys. 33 2179 (1992)]. Making use of this Q-function, we calculate the quadrature fluctuations of the optical system. From these results we infer that the signal–idler modes are in squeezed states. When the NDPO operates below threshold we show that, for a large squeezing parameter, a squeezing amounting to a noise suppression approaching 100% below the vacuum level in one of the quadratures can be achieved.     

Order-parameter collective modes in 3He-A and their effect on nuclear magnetic resonance (NMR) and ultrasonic attenuation

A generalization of our previous microscopic theory is used to derive the spin and density correlation functions for the Anderson-Brinkman-Morel (ABM) state. The coupling of the 18 fluctuation components of the order parameter due to the nuclear dipole interaction is taken into account rigorously. The results are valid for arbitrary temperature, frequency, wave number (with q parallel to the anisotropy axis), and magnetic field. Damping by pair-breaking processes is calculated explicitly; however, quasiparticle collisions are neglected. The frequencies of the clapping modes that couple to spin, and the frequencies of the flapping modes that couple to density, are found to split in a magnetic field. Near T _c the linewidth of the clapping mode and, at low T, the linewidth of the normal-flapping mode become small while the linewidth of the super-flapping mode is broad at all temperatures. The linewidth of the transverse NMR and the ultrasound attenuation coefficient, considered as functions of temperature, exhibit pronounced peaks at low temperatures. These arise from a coupling, induced by the dipole interaction, between spin or density fluctuations and the normal-flapping mode. Our results for the linewidth and line shift of the longitudinal NMR at low temperatures due to orbital effects are in agreement with results of Combescot.     

Quasi-photon Phase States

Abstract

We introduce quasi-photon phase states of radiation in the single mode, and study the fluctuations in the measured phase operators. We also show that these states exhibit bunching, unlike coherent states which show no bunching.     

Random Multimode Optical Media: I. Mode Coupling Process in Slab Waveguide with Stochastic Wall Perturbations

Abstract

The scope of the paper is to present in explicit form the mode coupling coefficients in slab waveguide, in the case when both boundaries of guiding core or gradient refractive index distribution are perturbed by random deviations from an ideal model. The central idea is to present the relationships between the processes, depicting the waveguide deformations and the estimators of the mode coupling processes. The correlation functions and the spectral density functions of both groups of processes are linearly interdependent; we examine the complex coefficients of these relations. In particular, the TE modes are analysed in detail in step-index slab. For the case of parabolic profile (n(x) = A(1 ? Bx²), within the core) the method which derives the statistic integral form of coupling coefficients is presented (also for guided TE modes). All modes are assumed to be monochromatic, i.e. time-dependence is exp (?iωt).     

Plasma Density Fluctuations and the Physics of Short-pulse Laser-produced Plasmas

Abstract

Laser-produced plasmas are studied for their relevance to laser fusion research, as bright pulsed sources of X-rays and fast particles, as well as for the fundamental plasma physics processes they reveal. The programme on laser-plasma-interaction physics at the Australian National University has gained prominence for elucidating the physics of plasmas generated using short laser pulses at very high intensity where complex nonlinear processes dominate behaviour. This review will discuss some of the results from that programme and in particular relate many of the observed phenomena to the existence of density fluctuations in the plasma.     

Interference in the Single Photon Regime

Abstract

The two orthogonally polarized modes of a Zeeman laser can be combined at a polarizing beam-splitter to produce two outputs at the difference frequency. This paper presents some observations on these beats in the classical limit and in the single photon regime, where the mean separation of the photons exceeds the optical path length, and discusses their implications.     

Using finite element analysis/optimum design in the determination of elastic constants by vibration testing

Abstract

Combining vibration testing and numerical methods is a potential alternative approach for determining elastic constants of materials because of nondestructive testing, single testing, and producing average properties. In order to simplify the modeling processes and to reduce complicated derivations in the numerical method, the combination of finite element analysis and optimum design is adopted in this work to inversely calculate the elastic constants. In this method, the effects of some parameters, including the finite element mesh, the mode number, constraints on state variables, the optimization method, and initial values and loops, are discussed. It is proved that the present method with 10×10 mesh, 6 vibration modes, 5% constraint on state variables, and subproblem approximation can obtain accurate results. Average values can be used to avoid the scatter in results due to different initial values, and do‐loops may not be necessary. It is also clearly demonstrated that the present method can correctly extract 2 or 5 elastic constants for isotropic or orthotropic materials.     

Scaling of decoherence effects in quantum computers

Abstract

The scaling of decoherence rates with qubit number N is studied for a simple model of a quantum computer in the situation where N is large. The two state qubits are localized around well-separated positions via trapping potentials and vibrational centre of mass motion of the qubits occurs. Coherent one and two qubit gating processes are controlled by external classical fields and facilitated by a cavity mode ancilla. Decoherence due to qubit coupling to a bath of spontaneous modes, cavity decay modes and to the vibrational modes is treated. A non-Markovian treatment of the short time behaviour of the fidelity is presented, and expressions for the characteristic decoherence time scales obtained for the case where the qubit/cavity mode ancilla is in a pure state and the baths are in thermal states. Specific results are given for the case where the cavity mode is in the vacuum state and gating processes are absent and the qubits are in (a) the Hadamard state (b) the GHZ state.     

Quantum Statistics of Stimulated Raman and Hyper-Raman Scattering of Squeezed Light with Pump Depletion

Abstract

Using the approximation of small fluctuations around a stationary solution, photon statistics and quadrature variances are derived in stimulated Raman and hyper-Raman scattering including the coupling of pumping, Stokes, anti-Stokes and phonon modes. The depletion of pump light is included. Compared to Raman scattering, additional regimes to generate anti-bunched, sub-Poisson and squeezed light were found caused by self-interaction of the pump mode. It was possible to include effects of nonlinear dynamics, initial squeezing of radiation and phonon system, external noise and losses.     

Non-classical Properties of Two-mode SU(1, 1) Coherent States

Abstract

We examine the non-classical properties of two-mode coherent states based on different unitary irreducible representations of SU(1, 1). Such states are generated by the action of the two-mode squeezing operator on initial states of the field containing arbitrary numbers of photons in each of the two modes. If the initial state of the field is a two-mode vacuum state, the final state is of course the two-mode squeezed vacuum. An initial occupation generalizes the idea of a squeezed vacuum to the SU(1, 1) coherent states. We show that fields in such states have remarkable quantum properties such as sub-Poissonian statistics, violations of the Cauchy-Schwarz inequality, strong correlations in the photon number fluctuations and squeezing. Using information theory formalism, we show that these coherent states are less correlated than the usual two-mode squeezed vacuum. Moreover, we show that an initial coherent amplitude contribution, in a large amplitude limit, can result in the reduction of correlations between modes.