Eduard Schmidt

Multilayer dielectric mirrors generated chirp in femtosecond dye-ringlasers

Abstract The phase modulation arising from multilayer dielectric laser mirrors of a fs-dye-ringlaser has been calculated and measured by the determination of an equivalent intracavity path length in glass. The main source for phase modulation in our laser system seems to be the saturable absorber.

OUANTUM-STATE TRANSFORMATION BY DISPERSIVE AND ABSORBING FOUR-PORT DEVICES

The recently derived input-output relations for the radiation field at a dispersive and absorbing four-port device [T. Gruner and D.-G. Welsch, Phys. Rev. A 54, 1661 (1996)] are used to derive the unitary transformation that relates the output quantum state to the input quantum state, including radiation and matter and without placing frequency restrictions. It is shown that for each frequency the transformation can be regarded as a well-behaved SU(4) group transformation that can be decomposed into a product of U(2) and SU(2) group transformations. Each of them may be thought of as being realized by a particular lossless four-port device. If for narrow-bandwidth radiation far from the medium resonances the absorption matrix of the four-port device can be disregarded, the well-known SU(2) group transformation for a lossless device is recognized. Explicit formulas for the transformation of Fock-states and coherent states are given.

Evolution of spatial solitons in quadratic media with fluctuating nonlinearity

The influence of a fluctuating nonlinearity on the propagation of spatial solitons in quadratic media is studied. We derive mean field evolution equations for both frequency components and show that fluctuations of the nonlinearity induce effective nonlinear losses. The predictions of the mean field theory are in good agreement with numerical simulations of the full stochastic system. We find an approximate analytical expression for the damping rate of spatial solitons and show that the amplitude of the fundamental wave decreases more rapidly than the amplitude of the second harmonic.

Quantum theory of light in nonlinear media with dispersion and absorption

We present a canonical quantum theory of radiation in nonlinear media taking into account the effects of linear dispersion and absorption in a consistent way. We start from a-microscopic model and apply recently developed concepts of the quantization of radiation in dispersive and absorbing linear media and extend the theory in order to include nonlinear optical processes. We derive propagation equations in space and time for the quantized radiation field, with special emphasis on the propagation of quantum-light pulses in Kerr media. In particular, the method enables us to derive systematically the noise sources that arise naturally in the nonlinear terms.

Cumulant expansion for studying damped quantum solitons

The quantum statistics of damped optical solitons is studied using cumulant-expansion techniques. The effect of absorption is described in terms of ordinary Markovian relaxation theory, by coupling the optical field to a continuum of reservoir modes. After introduction of local bosonic field operators and spatial discretization pseudo-Fokker-Planck equations for multidimensional s-parameterized phase-space functions are derived. These partial differential equations are equivalent to an infinite set of ordinary differential equations for the cumulants of the phase-space functions. Introducing an appropriate truncation condition, the resulting finite set of cumulant evolution equations can be solved numerically. Solutions are presented in Gaussian approximation and the quantum noise is calculated, with special emphasis on squeezing and the recently measured spectral photon-number correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].

Propagation of entangled light pulses through dispersing and absorbing channels

The problem of decorrelation of entangled (squeezed-vacuum-type) light pulses of arbitrary shape passing through dispersive and absorbing four-port devices of arbitrary frequency response is studied, applying recently obtained results on quantum-state transformation (L Knoll et al 1999 Phys. Rev. A 59 4716). The fidelity and indices of (quantum) correlation based on the von Neumann entropy are calculated, with special emphasis on the dependence on the mean photon number, the pulse shape and the frequency response of the devices. In particular, it is shown that the quantum correlations can decay very rapidly due to dispersion and absorption, and the degree of degradation intensifies with increasing mean photon number.

Partitioning optical solitons for generating entangled light beams

Abstract It is shown that the two beams generated by bipartition of an optical soliton are entangled. The amount of entanglement obtained by bipartition of an N -bound soliton ( N =2,3) can be substantially larger than that in bipartition of the fundamental soliton ( N =1). An analysis of the mode structure of the entangled beams shows that typically N modes in each beam contribute to the entanglement. In particular, partitioning of the fundamental soliton effectively produces two-mode squeezed light.

Quantum noise of damped N-solitons

The photon-number statistics of damped higher-order optical solitons are studied numerically, using cumulant-expansion techniques in Gaussian approximation. The analysis is given in both the time domain and the frequency domain. Introducing appropriate filtering, it is shown that the photon-number noise can be strongly nonclassically correlated to each other. In particular, filter optimization is performed in order to observe strong sub-Poissonian statistics and strong nonclassical correlations.

Nonclassical correlations in damped quantum solitons

The internal quantum statistics of damped soliton-like pulses in Kerr media are studied numerically, considering both narrow- and finite-bandwidth spectral pulse components. It is shown that both the photon-number correlation and the correlation of the photon-number variance between different pulse components can be highly nonclassical even for absorbing fibres. Optimum frequency windows are determined in order to realize strong nonclassical behaviour, which offers novel possibilities of using solitons in optical fibres as a source of nonclassically correlated light beams.

Two-pulse correlations in noisy quantum channels

The modification of initially entangled light pulses passing through noisy quantum channels, modeled by dispersive and absorbing four-port devices, is studied with the help of recently obtained results on quantum state transformations. The fidelity and indices of quantum correlations based on the von Neumann entropy are calculated. Their dependence on both the pulse shape and the four-port device parameters is studied. It is shown that due to dispersion and absorption, the quantum correlations are reduced, and they decrease with increasing initial entanglement.