Editorial for Special Issue on Multiphoton Processes

<正>With the rapid development of ultrafast intense laser technologies,the interaction of intense laser radiation with matter has been a frontier for few decades.The International Conference on Multiphoton Processes(ICOMP).initiated in 1977,covers the latest advances in the field every three years.The special issue is based on the spirit of the 13th International Conference on Multi-Photon Processes,ICOMP13.which was held in Shanghai,organized by Shanghai     

介质腔中场-原子作用系统密度算符间距的演化

利用密度算符间距的概念,关注克尔介质腔中非关联双模相干态光场与V形三能级原子相互作用系统中两子系统(原子和光场)间的信息差异,通过数值计算、图形分析,讨论了不同的原子初始态和克尔效应对系统以及子系统密度算符间距的时间演化特性的影响,结果表明:首先,当不存在克尔介质时,无论原子初始处于哪种状态,系统和原子密度算符间距的振荡均呈现崩塌、复原现象.其次,随着克尔效应的增强,(1)原子初始态为激发态时,系统中原子和光场密度算符间距的演化曲线呈现周期性变化,且克尔效应越强周期性越明显;(2)原子初态为基态时,原子间距的演化曲线逐渐变成一条直线,原子末态几乎不随时间变化,处于稳态,光场间距的演化曲线在不断振荡.最后,激发态和基态原子两种情况下,随着克尔效应的增强,原子间距的值越来越小,即原子末态离初态愈来愈"近",表现了克尔介质的态囚禁效应;光场间距的值增大,即光场末态离初态越来越"远";系统间距的演化曲线保持在1,即在正交态附近振荡.     

Multiphoton Processes at the Induced Inverse Bremsstrahlung in Dense Plasmas

Electron energy absorption in laser irradiated plasma is determined by sum of rates of multiphoton induced absorption and emission. These rates contain squares of the Bessel functions. It was shown that in moderate laser field terms with absorption and emission of several photons are large, but cancel exactly each to other. Therefore we should take into account terms with absorption and emission of only one laser photon (first order perturbation theory). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Exact Solution for a Multiphoton Generalized Jaynes-Cummings Model with Inverse Operators

A new exactly solvable multiphoton generalized Jaynes-Cummings model is presented, whose Hamiltonian is related to the inverse of field mode creation and annihilation operators. Then we use supersymmetric unitary operators to diagonalize the Hamiltonian above and obtain their energy spectra and eigenstates. In addition, its pseudo-invariant eigen-operator is found as well, directly leading to the corresponding energy-level gap.     

Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED

We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.     

Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED

We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.     

Conditional Probabilities and Density Operators in Quantum Modeling

Motivated by a recent proof of free choices in linking equations to the experiments they describe, I clarify some relations among purely mathematical entities featured in quantum mechanics (probabilities, density operators, partial traces, and operator-valued measures), thereby allowing applications of these entities to the modeling of a wider variety of physical situations. I relate conditional probabilities associated with projection-valued measures to conditional density operators identical, in some cases but not in others, to the usual reduced density operators. While a fatal obstacle precludes associating conditional density operators with general non-projective measures, tensor products of general positive operator-valued measures (POVMs) are associated with conditional density operators. This association together with the free choice of probe particles allows a postulate of state reductions to be replaced by a theorem. An application shows an equivalence between one form of quantum key distribution and another with respect to certain eavesdropping attacks.     

Multiphoton Processes of Two Modes of Quantized Field Interaction with Interacting Asymmetric Two Two-Level Atoms

International Journal of Theoretical Physics - The interaction between two modes quantized field and asymmetric two atoms represents one of the important quantum models to study the nonclassical...     

Transformations on Density Operators That Leave the Holevo Bound Invariant

For a given probability distribution λ ₁,…,λ _m we determine the structure of all such maps defined on a dense subset of density operators which leave the Holevo bound invariant i.e. which satisfy $$S\Biggl(\sum_{k=1}^m \lambda_k \phi(\rho_k)\Biggr)- \sum_{k=1}^m \lambda_k S\bigl(\phi (\rho_k)\bigr)= S\Biggl(\sum _{k=1}^m \lambda_k \rho_k\Biggr)- \sum_{k=1}^m \lambda_k S(\rho_k) $$ for all possible collections ρ ₁,…,ρ _m of density operators.     

Partial Trace Method for Deriving Density Operators of Light Field

With the help of technique of integration within an ordered product of operators we can fully display the partial trace method to deduce some new density operators of light field. The general form of single-mode density operator is derived in this way from a normalized two-mode generalized squeezed pure state density operator.     

Differential-Form Relations Between Density Operators and Their P-Representations in Coherent State Basis

By virtue of the technique of integration within an ordered product of operators, we derive differential-form relations between density operators and their P-representations in the coherent state basis. Some applications of these new relations in normally ordering operators are given.     

Multiphoton transitions between energy levels in a current-biased Josephson tunnel junction

The escape of a current-biased Josephson tunnel junction from the zero-voltage state in the presence of weak microwave radiation is investigated experimentally at low temperatures. The measurements of the junction switching current distribution indicate the macroscopic quantum tunneling of the phase below a crossover temperature of T small star, filled approximately 280 mK. At temperatures below T small star, filled we observe both single-photon and multiphoton transitions between the junction energy levels by applying microwave radiation in the frequency range between 10 and 38 GHz to the junction. These observations reflect the anharmonicity of the junction potential containing only a small number of levels.     

Multiphoton conductivity in KBr

Multiphoton conductivity measurements at room temperature on KBr monocrystals are reported. The experimental results show evidence of two- and four-photon processes and confirm the assignment of the optical gap obtained by means of two-photon spectroscopy.     

Quantum Geometry on Quantum Spacetime: Distance,Area and Volume Operators

We develop the first steps towards an analysis of geometry on the quantum spacetime proposed in Doplicher et al. (Commun Math Phys 172:187–220, 1995). The homogeneous elements of the universal differential algebra are naturally identified with operators living in tensor powers of Quantum Spacetime; this allows us to compute their spectra. In particular, we consider operators that can be interpreted as distances, areas, 3- and 4-volumes.     

Short Distance Scale Invariance,High Energy Processes and Elementary Particles

Within the framework of quantum field theory (QFT) with the Yukawa type of interactions of baryons and mesons a method is proposed which allows one to take into account the effects of short distance scale invariance in observable processes on the mass shell. In this theory the scale invariance is equivalent to the finite renormalization of coupling constants. The method is based on the investigation of asymptotics of diagrams and on the summation of all logarithmic terms of all diagrams. The general picture of high energy processes is in qualitative agreement with the present experimental situation, however, it manifests some peculiarities:

• a For the scattering at small angles we obtain the modified Regge picture with fixed branch points of the \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {i - i_0 } $\end{document} type in addition to the Regge poles. One of these branch points could be a good candidate for the Pomeranchuk singularity, the others are useful for some more delicate details of the scattering (e.g. polarization in the π N-charge exchange).
• b The large angle scattering cross section decreases as a power of energy.
• c The Bjorken scaling in the deep inelastic ep-scattering is not a direct effect of scale invariance and can be broken due to the factor (−q²)^lγ.
• d For the inclusive processes the modified Regge picture is obtained. The large transverse momentum distribution decreases as a power of q ⟂.
• e A weak power growth of multiplicity and logarithmic growth of average transverse momenta are possible.
• f In addition to the composite, reggeized particles there are some elementary mesons and nucleons which explain the peculiarities of the reactions with their exchange.

     

Multiphoton transitions in direct-gap semiconductors

Multiphoton transitions in direct-gap semiconductors are studied considering a “non-perturbative” approach in which the final state is represented by a Volkov wavefunction. Analytical solutions are obtained for multiphoton transition rates. The relation between multiphoton absorption and tunneling is discussed.     

Discontinuities of the Integrated Density of States for Random Operators on Delone Sets

Despite all the analogies with usual random models, tight binding operators for quasicrystals exhibit a feature that clearly distinguishes them from the former: the integrated density of states may be discontinuous. This phenomenon is identified as a local effect, due to the occurrence of eigenfunctions with bounded support.Research partly supported by the DFG in the priority program Quasicrystals