Multimode description of stimulated parametric down-conversion

We derive multimode generating functions, photon-number distributions, integrated-intensity distributions, moments and quadrature fluctuations for stimulated parametric down-conversion in relation to experiments measuring joint distributions. The border between classical and quantum behaviour is given.     

Bright entanglement and the Einstein-Podolsky-Rosen paradox with coupled parametric oscillators

We show that two evanescently coupled χ⁽²⁾ parametric oscillators provide a tunable bright source of quadrature squeezed light, Einstein-Podolsky-Rosen correlations and quantum entanglement. Analysing the system in the above threshold regime, we demonstrate that these properties can be controlled by adjusting the coupling strengths and the cavity detunings. As this can be implemented with integrated optics, it provides a possible route to rugged and stable EPR sources.     

Formal equivalence between Tsallis and extended Boltzmann-Gibbs statistics

A formal correspondence between the q-distribution obtained from the Tsallis entropy and non-Maxwellian distributions obtained from the Boltzmann-Gibbs (BG) entropy is obtained. This formal correspondence is obtained by imposing an infinite number of constraints when one maximizes the BG entropy. Different from the approach of Tsallis, Prato and Plastino [C. Tsallis, D. Prato, A.R. Plastino, Astrophys. Space Sci., 290 (2004) 259-274], we relate the constraints to the central moments, providing a natural meaning to the q-parameter.     

Decoherence in strongly coupled quantum oscillators

In this paper, we present a comprehensive analysis of the coherence phenomenon of two coupled dissipative oscillators. The action of a classical driving field on one of the oscillators is also analyzed. Master equations are derived for both regimes of weakly and strongly interacting oscillators from which interesting results arise concerning the coherence properties of the joint and the reduced system states. The strong coupling regime is required to achieve a large frequency shift of the oscillator normal modes, making it possible to explore the whole profile of the spectral density of the reservoirs. We show how the decoherence process may be controlled by shifting the normal mode frequencies to regions of small spectral density of the reservoirs. Different spectral densities of the reservoirs are considered and their effects on the decoherence process are analyzed. For oscillators with different damping rates, we show that the worse-quality system is improved and vice versa, a result which could be useful for quantum state protection. State recurrence and swap dynamics are analyzed as well as their roles in delaying the decoherence process.     

A degenerate three-level laser with a parametric amplifier

The aim of this paper is to study the squeezing and statistical properties of the light produced by a degenerate three-level laser whose cavity contains a degenerate parametric amplifier. In this quantum optical system the top and bottom levels of the three-level atoms injected into the laser cavity are coupled by the pump mode emerging from the parametric amplifier. For a linear gain coefficient of 100 and for a cavity damping constant of 0.8, the maximum intracavity squeezing is found at steady state and at threshold to be 93%.     

Noise analysis in correlated imaging, quantum and classical

The theoretical analysis of the noise property is presented in a correlated imaging system. For both entangled source produced by parametric down-conversion (PDC) and classically light source, a small aperture of the imaging system makes the noise increase slightly and the resolution of the imaging signal degrade. We also show that, in PDC case, the noise is strongly influenced by the source size because of the existence of the entanglement, while the effect is not obvious in the thermal case.     

Unsolved problems in quantum optics (several short notes)

The possible prospects for the improvement of the resolution and of the sensitivity in quantum-optics experiments are discussed as well as possible applications of quantum-optics methods for the solution of fundamental physical problems.Dedicated to H. Walther on the ocassion of his 60th birthday     

On a heuristic point of view related to quantum nonequilibrium statistical mechanics

In this paper I propose a new way for counting the microstates of a system out of equilibrium. As, according to quantum mechanics, things happen as if a given particle can be found in more than one state at once, I extend this concept to propose the coherent access by a particle to the available states of a system. By coherent access I mean the possibility for the particle to act as if it is populating more than one microstate at once. This hypothesis has experimental implications, since the thermodynamical probability and, as a consequence, the Bose-Einstein distribution as well as the argument of the Boltzmann factor is modified.     

Generation of pulsed squeezed light in a mode-locked optical parametric oscillator

The generation of pulsed squeezed light using an optical parametric oscillator (OPO) is discussed. This mode-locked optical parametric oscillator consists of a nonlinear crystal in a cavity which is resonant for both signal and idler waves and which is synchronously pumped by the second-harmonic of an acousto-optically mode-locked cw Nd: YAG laser. The fundamental wavelength of the pump laser provides local oscillator pulses for balanced homodyne detection of squeezed vacuum pulses emitted by the oscillator when operated below oscillation threshold. Photocurrent noise reduction to 30% below the classical shot-noise limit is observed, corresponding to squeezing of the field to a level approximately a factor of two below the mean square vacuum noise.     

Tunable coupled plasmon modes via nanoshell particle chains

Coupled plasmon modes have been studied theoretically in periodic chains of nanoshell particles embedded in a graded dielectric host. These chains not only sustain a variety of localized modes as unshelled nanoparticle chains, but also offer precise control of the localization-delocalization transition among these modes by varying the permittivity contrast and/or core-shell radius ratio. By optimizing these parameters, the upper band can be tuned into higher frequencies while the lower band can be tuned into the optical communication frequencies for practical application. We also discuss the Ohmic loss effects in the metallic component of the nanoshells.     

Dynamics of quantum observables in entangled states

We examine the dynamics of a radiation field propagating through a nonlinear medium. A time series analysis of the mean photon number illustrates how an open quantum system interacting with a quantum environment can exhibit remarkably diverse ergodicity properties, both nonlinearity and departure from coherence playing a crucial role.     

Number-phase entropic uncertainty relations and Wigner functions for solvable quantum systems with discrete spectra

In this Letter, the “number-phase entropic uncertainty relation” and the “number-phase Wigner function” of generalized coherent states associated to a few solvable quantum systems with non-degenerate spectra are studied. We also investigate time evolution of “number-phase entropic uncertainty” and “Wigner function” of the considered physical systems with the help of temporally stable Gazeau-Klauder coherent states.     

Guiding and high-harmonic generation of sub-10-fs pulses in hollow-core fibers at 1015 W/cm2

15 W/cm². The high resistance of fused silica to damage in the sub-10-fs regime allows stable reproducible operation without degradation of the capillary waveguide. In preliminary experiments, we demonstrate kHz-repetition-rate guided-wave high-harmonic generation in helium down to the 10-nm range. The reported experiments open up the way to realizing high-field interactions with plane-wave excitation at intensity levels in excess of 10¹⁵ W/cm² under well-controlled conditions. Received: 28 May 1998     

Deterministic geometric quantum phase gates for two atoms in decoherence-free subspace

We propose a scheme for realizing conventional geometric quantum phase gates in the context of cavity QED. During the operation neither the atomic system nor the cavity mode is excited, which is important in view of decoherence. The scheme does not require detection of photons, so the gate operation is deterministic and the influence of photodetection imperfection is eliminated. Taking advantage of the geometric manipulation, the phase gate is resilient to fluctuations of experimental parameters.     

Method for generating a new class of multipartite entangled state in cavity quantum electrodynamics

Recently, Yeo and Chua introduced a genuine four-qubit entangled state |χ〉 which can implement perfect teleportation of an arbitrary two-qubit state [Y. Yeo, W.K. Chua, Phys. Rev. Lett. 96 (2006) 060502]. It has been shown that the state |χ〉 is inequivalent to the well-known Greenberger-Horne-Zeilinger state, W state, and linear cluster state, in terms of stochastic local operations and classical communication [C.F. Wu, Y. Yeo, L.C. Kwek, C.H. Oh, Phys. Rev. A 75 (2007) 032332]. This “new” class of state has many interesting entanglement properties and possible applications in quantum-information processing and fundamental tests of quantum mechanics. Here, we propose a simple scheme to generate the state |χ〉 in cavity quantum electrodynamics. Our idea may be helpful for in-depth study on such a class of state and its practical applications.     

Relaxation- and decoherence-free subspaces in networks of weakly and strongly coupled resonators

We consider a network of interacting resonators and analyze the physical ingredients that enable the emergence of relaxation-free and decoherence-free subspaces. We investigate two different situations: (i) when the whole network interacts with a common reservoir and (ii) when each resonator, strongly coupled to each other, interacts with its own reservoir. Our main result is that both subspaces are generated when all the resonators couple with the same group of reservoir modes, thus building up a correlation (among these modes), which has the potential to shield particular network states against relaxation and/or decoherence.     

Quantum phase properties associated to solvable quantum systems using the nonlinear coherent states approach

In this paper we study the quantum phase properties of “nonlinear coherent states” and “solvable quantum systems with discrete spectra” using the Pegg-Barnett formalism in a unified approach. The presented procedure will then be applied to few special solvable quantum systems with known discrete spectrum as well as to some new classes of nonlinear oscillators with particular nonlinearity functions. Finally the associated phase distributions and their nonclasscial properties such as the squeezing in number and phase operators have been investigated, numerically.