Input-output Formalism Research Articles

Transverse Effects on Squeezing with Atoms

We evaluate the squeezing of a probe beam with a transverse Gaussian structure interacting with an ensemble of two-level atoms in a cavity. We use the linear input-output formalism where the effect of atoms is described by susceptibility and noise functions, and show that the transverse structure is accounted for by averaging these atomic functions over the intensity profile. The results of the plane-wave and Gaussian-wave theories are compared. We find that, when a large squeezing is predicted, the prediction of the plane-wave model is not reliable outside the Kerr domain. We give an estimate of the squeezing degradation due to the Gaussian transverse structure.

Examples of Stabilization using Saturation: An Input-Output Approach

This note presents three examples where input-output stability arguments can be used to deduce global asymptotic stability for the equilibrium of a nonlinear ordinary differential equation (o.d.e.). The examples are the ball and beam with friction, the planar vertical takeoff and landing aircraft and the inverted pendulum on a cart. We also discuss a general input-output formalism which is especially relevant for these examples.

Output quantum correlations of frequency nondegenerate parametric amplifiers with asymmetric losses

We consider a parametric interaction inside a lossy cavity exciting two modes symmetrically placed with respect to a high carrier frequency. An input-output formalism is used to derive the spectrum of the fluctuations outside the cavity below the threshold limit in the quadrature phase amplitude representation proposed by Caves. An analysis of the combined effects of frequency detuning of the sidemodes and asymmetry of the cavity mirror transmission losses on the noise distribution in the transmitted fields is presented. The sensitivity of the Einstein-Podolsky-Rosen correlations on the asymmetry of the losses is presented in a separate paper.

Quantum Langevin equations for a two-mode parametric amplifier: Noise squeezing without negative diffusion.

The theory of a two-mode nondegenerate parametric amplifier in a cavity is reformulated in terms of quadrature-phase-amplitude variables. The corrrespondence with a genuine classical stochastic linear process is found (non-negative-definite diffusion matrices) for the case of a cavity device immersed in thermal or ordinary (nonsqueezed) vacuum sources. A special kind of squeezing, i.e., quadrature squeezing [B. L. Schumaker, Phys. Rep. 135, 318 (1986)], is found to be characteristic of the internal steady state for the case of a cavity model subjected to an additional phase-sensitive noise source coupled to one of the two internal modes. Finally, the usual squeezing spectrum of the output field is calculated in both cases by means of an input-output formalism based upon a symmetric ordering scheme of noncommuting operators, well adapted for the quadrature-phase description of the fields involved in the interaction.

Generation of sub-Poissonian light using active control with twin beams.

We present a general theory for intensity noise reduction when one beam of light is used to control another. We use a semiclassical input-output formalism and determine the conditions necessary for noise reduction below the shot-noise level. Configurations are examined where the intensity of one beam is monitored and control is effected directly to the other beam (feedforward), or indirectly through the beam source (feedback). The results are applied to the case of twin beams generated by an optical parametric oscillator. We detail for this system the implementation of an electro-optic control channel. Finally, a comparison is made between theory and experiment.

Input and output in damped quantum systems II Methods in non-white-noise situations and application to inhibition of atomic phase decays

A near-white-noise input–output formalism is developed that does not require white-noise assumptions. In particular, correlation formulas for outputs are developed, which enables account to be taken of reflections of near-white-noise inputs. The methods are applied to the inhibition of atomic phase decays by squeezed light from a degenerate parametric amplifier incident upon a two-level atom, and modifications from previous work carried out in the extreme-white-noise limit are computed.