Berry phases in the three-level atoms driven by quantized light fields

A theoretical analysis of Berry’s phases is given for the three-level atoms interacting with external one-mode and two-mode quantized light fields. Three main results are obtained: (i) There is a Berry phase which vanishes in the classical limit or this Berry phase is completely induced by the field quantization; (ii) Berry’s phases for the one-mode field and the two-mode field can be equal so long as the photon numbers of the two-mode field are properly chosen; (iii) In the two-mode case, Berry phases of the atom interacting with one mode is affected by the other mode even if the photon number of the other mode is zero.      

Quantum interferences in four-wave mixing processes inside a cavity driven by quantized fields

Interferences in the quantum fluctuations of the output fields are demonstrated in four-wave mixing processes inside a cavity,which is driven by two quantized fields at the signal and the idler frequencies.These interferences depend on the phase fluctuations of the input fields and induce mode splitting in the transmission spectra.     

Homopolar oscillating-disc dynamo driven by parametric resonance

We use a simple model of Bullard-type disc dynamo, in which the disc rotation rate is subject to harmonic oscillations, to analyze the generation of magnetic field by the parametric resonance mechanism. The problem is governed by a damped Mathieu equation. The Floquet exponents, which define the magnetic field growth rates, are calculated depending on the amplitude and frequency of the oscillations. Firstly, we show that the dynamo can be excited at significantly subcritical disc rotation rate when the latter is subject to harmonic oscillations with a certain frequency. Secondly, at supercritical mean rotation rates, the dynamo can also be suppressed but only in narrow frequency bands and at sufficiently large oscillation amplitudes.     

On certain non-relativistic quantized fields

We consider a Euclidean invariant interaction Hamiltonian which is a polynomial in smeared Fermion field operators (the smearing function providing an ultraviolet cut-off). By considering Guenin's perturbation series for the time-development of the theory, we show that time-displacements define a one-parameter group of automorphisms of the field algebra att=0, which acts continuously in the time-parameter. Results are obtained for any dimension of space and for both relativistic and nonrelativistic forms for the free Hamiltonian. In special cases the total Hamiltonian is a positive self-adjoint operator in Fock space, thus defining a concrete non-relativistic quantized field with non-trivial particle production.Supported in part by the United States Air Force under contract AFOSR 500-66.     

Nonlinear interactions and quantum entanglement for collective fields in near-resonantly driven systems

This paper proposes a novel form of multimode nonlinear interactions by using a near-resonantly dressed atomic ensemble in an optical cavity.Due to quantum interference,a pair of collective fields come into the bilinear interactions,whose strengths are proportional to the population difference between dressed states which are coupled to the collective fields.By such an interaction,it is possible to obtain perfect multimode squeezing and collective Einstein-Podolsky-Rosen(EPR) entanglement in the cavity output.     

Relativistic quantum theory without quantized fields

Peculiarities of symmetrical quantum systems are considered with the aid of the Mackey's induced representations theory. The four-dimensional coordinate representation of the relativistic quantum mechanics suggested by Stueckelberg in 1941 is rederived, reinterpreted and generalized for an arbitrary spin. Then it is applied to introduce the causal propagator as a particleantiparticle transition amplitude without consideration of a field equation. Finally the theory of relativistic quantum particles interaction is reformulated without an appeal to the concept of quantized fields.     

Correlation functions near instabilities in systems driven by parametric noise

For a quantum system weakly coupled to heat reservoirs, a statistical mechanical theory is developed in a formalism that dovetails perfectly with phenomenological thermodynamics. The present model is a modification of the many-reservoir model by Bergmann and Lebowitz. The method to be used here is based on the explicit introduction of external forces which bring about a deviation from equilibrium. These forces are assumed to arise from mechanical interaction with its surrounding which can be characterized thermodynamically. By an appropriate choice of reservoirs the Liouville-von Neumann equation is found to describe a heat conducting system. The nonequilibrium density matrices which describe such a system are found explicitly for some interesting cases. With these density matrices we obtain an expression for entropy production.     

Phase transitions driven by quasiparticle interactions

After a survey of the solid–liquid transition, driven by phonon–phonon interactions, attention is next focussed on two phase transitions caused by electron–phonon interactions. These are (i) the Barden–Cooper–Schrieffer pure metal superconducting transition and (ii) the original Peierls instability. These have closely similar forms for the respective transition temperatures, both being related to energy gaps. Spin–phonon interactions are then discussed in relation to spin-Peierls materials. Finally, magnon–magnon interactions are treated in the context of the ferromagnetic–paramagnetic transition in the itinerant electron systems Fe, Co and Ni. Heuristic and phenomenological arguments, plus of course experiment, provide the basis for the conclusions drawn here.     

Coherent polarization driven by external electromagnetic fields

The coherent interaction of the electromagnetic radiation with an ensemble of polarizable, identical particles with two energy levels is investigated in the presence of external electromagnetic fields. The coupled non-linear equations of motion are solved in the stationary regime and in the limit of small coupling constants. It is shown that an external electromagnetic field may induce a macroscopic occupation of both the energy levels of the particles and the corresponding photon states, governed by a long-range order of the quantum phases of the internal motion (polarization) of the particles. A lasing effect is thereby obtained, controlled by the external field. Its main characteristics are estimated for typical atomic matter and atomic nuclei. For atomic matter the effect may be considerable (for usual external fields), while for atomic nuclei the effect is extremely small (practically insignificant), due to the great disparity in the coupling constants. In the absence of the external field, the solution, which is non-analytic in the coupling constant, corresponds to a second-order phase transition (super-radiance), which was previously investigated.     

Qubit entanglement driven by remote optical fields

We examine the entanglement between two qubits, supposed to be remotely located and driven by independent quantized optical fields. No interaction is allowed between the qubits, but their degree of entanglement changes as a function of time. We report a collapse and revival of entanglement that is similar to the collapse and revival of single-atom properties in cavity QED.     

On the construction of quantized gauge fields

In this paper the construction of the two-dimensional abelian Higgs model begun in two earlier articles is completed. First we show how to remove the remaining ultraviolet cutoff on the gauge field, then we construct the infinite volume limit and verify the axioms of Osterwalder and Schrader for the expectation values of gauge invariant local fields. Finally it is shown that an auxiliary gauge field mass that was introduced to avoid infrared problems can be safely removed.Research supported in part N.S.F. Grant MCS 79-02490Research partly supported by Centre National de la Recherche Scientifique     

Hot-electron transport in graphene driven by intense terahertz fields

We investigate transport properties of graphene driven by intense terahertz (THz) fields, considering impurity, acoustic-phonon and optical phonon scatterings. The time evolutions of drift velocity and electron temperature are analyzed and the phase shift and distortion of drift velocity are demonstrated. We also examine the terahertz photoconductivity, finding that the suppression of linear dc mobility is greatly enhanced with decreasing frequency of the radiation.     

Second quantized scalar QED in homogeneous time-dependent electromagnetic fields

We formulate the second quantization of a charged scalar field in homogeneous, time-dependent electromagnetic fields, in which the Hamiltonian is an infinite system of decoupled, time-dependent oscillators for electric fields, but it is another infinite system of coupled, time-dependent oscillators for magnetic fields. We then employ the quantum invariant method to find various quantum states for the charged field. For time-dependent electric fields, a pair of quantum invariant operators for each oscillator with the given momentum plays the role of the time-dependent annihilation and the creation operators, constructs the exact quantum states, and gives the vacuum persistence amplitude as well as the pair-production rate. We also find the quantum invariants for the coupled oscillators for the charged field in time-dependent magnetic fields and advance a perturbation method when the magnetic fields change adiabatically. Finally, the quantum state and the pair production are discussed when a time-dependent electric field is present in parallel to the magnetic field.     

Room-temperature polariton parametric scattering driven by a one-dimensional polariton condensate

We demonstrate a novel way to realize room-temperature polariton parametric scattering in a one-dimensional ZnO microcavity. The polariton parametric scattering is driven by a polariton condensate, with a balanced polariton pair generated at the adjacent polariton mode. This parametric scattering is experimentally investigated by the angle-resolved photoluminescence spectroscopy technique under different pump powers and it is well described by the rate equation of interacting bosons. The direct relation between the intensity of the scattered polariton signal and that of the polariton reservoir is acquired under nonresonant excitation, exhibiting the explicit nonlinear characteristic of this room-temperature polariton parametric process.     

High order harmonics driven by a self-phase-stabilized IR parametric source

We analyze the emission of coherent XUV radiation in gaseous targets by high-order harmonics of tunable infrared (1.4–1.6 μm) laser pulses generated by a parametric source. As noticeable application, we show that a continuous spectrum spanning the 40–200 eV region can be efficiently generated by mixing the infrared pulses with visible pulses at 800 nm. These results open new perspectives for the extension of attosecond physics towards the soft-X region and for the investigation of atoms and molecules on a broader range of photon energies with respect to the state of the art.     

Optimized translation of microbubbles driven by acoustic fields

The problem of a single acoustically driven bubble translating unsteadily in a fluid is considered. The investigation of the translation equation identifies the inverse Reynolds number as a small perturbation parameter. The objective is to obtain a closed-form, leading order solution for the translation of the bubble, assuming nonlinear radial oscillations and a pressure field as the forcing term. In a second part, the periodic attractor of the Rayleigh-Plesset equation serves as basis for an optimal acoustic forcing designed to achieve maximized bubble translation over one dimensionless period. At near-resonant or super-resonant driving frequencies, it seems one cannot improve much on sinusoidal forcing. However at moderate acoustic intensity and sub-resonant frequencies, acoustic wave forms that enhance bubble collapse lead to displacement many times larger than the case of purely sinusoidal forcing. The survey covers a wide spectrum of driving ratios and bubble diameters including those relevant to biomedical applications. Shape stability issues are considered. Together, these results suggest new ways to predict some of the direct and indirect effects of the acoustic radiation force in applications such as targeted drug delivery, selective bubble driving, and accumulation.     

超快强激光驱动的原子分子电离

强场电离是超快强激光与物质相互作用时发生的基本物理过程。强场驱动原子分子的电离电子动力学过程发生在一个光学振荡周期以内,是在阿秒时间尺度上研究电子超快动力学的典范。不仅如此,强场驱动下的超短电子束还为探测原子分子的结构及其超快动力学提供了重要的技术手段。文章首先简要阐述了超快强光场中原子分子电离的基本物理图像,在此基础上,介绍了近年来基于强场电离电子开展的超快过程研究的几个例子,最后简要讨论了强场电离研究的未来可能发展方向。