Duration and non-locality of a nucleon-nucleon collision

For a set of realistic nucleon-nucleon potentials we evaluate microscopic parameters of binary collisions: a time duration of the scattering state, a mean distance and a rotation of nucleons during a collision. These parameters enter the kinetic equation as non-instantaneous and non-local corrections of the scattering integral, i.e., they can be experimentally tested. Being proportional to off-shell derivatives of the scattering T-matrix, non-instantaneous and non-local corrections make it possible to compare the off-shell behavior of different potentials in a vicinity of the energy shell. The Bonn one-Boson-exchange (A-C) and Paris potentials are found to yield very close results, while the separable Paris potential differs.Comment: Phys. Rev. C su

Realistic Calculations of Excitations in Nuclear Matter

A numerical method has been developed to solve the RPA equation, exchange term included, in nuclear matter. The dynamic form factor S(q, ω) is extracted for several v4 and v6 phenomenological potentials, including the d1-potential of Gogny et al. The limits of validity of the long-wavelength (Landau) approximation and the often adopted local-kernel approximation are discussed. Substantial disagreements with the exact results are found for the latter. The method is then applied to solve a Jastrow-correlated extension of the RPA equation, using the hardcore OMY potential. Results of calculations performed in two-body cluster approximation and Fermi-Hypernetted-Chain (FHNC) approximation are compared. The two-body results predict an instability against density fluctuations, which disappears at the FHNC level. The validity and consequences of employing the FHNC effective potential within the self-consistent HF/RPA framework are discussed. Future developments include applying the method to other Fermi systems such as liquid 3He and the microscopic calculation of Landau parameters.</p

Collective terahertz fluctuation modes in a polariton laser

A polariton Bardeen-Cooper-Schrieffer (BCS) state in a semiconductor microcavity is an example of symmetry-broken states in open systems. Fluctuations of the order parameter are an important tool to characterize such a state. With the condensate formed by composite particles, the set of zero-momentum fluctuations spans an infinite-dimensional electron-hole mode subspace. We show that collective fluctuation modes with orbital angular momentum different from that of the order parameter can be obtained with terahertz radiation, and that a physical manifestation of such modes, which are not Higgs modes, can be terahertz gain.Comment: 23 pages, 13 figure

Optically controlled orbital angular momentum generation in a polaritonic quantum fluid

Applications of the orbital angular momentum (OAM) of light range from the next generation of optical communication systems to optical imaging and optical manipulation of particles. Here we propose a micron-sized semiconductor source which emits light with pre-defined OAM components. This source is based on a polaritonic quantum fluid. We show how in this system modulational instabilities can be controlled and harnessed for the spontaneous formation of OAM components not present in the pump laser source. Once created, the OAM states exhibit exotic flow patterns in the quantum fluid, characterized by generation-annihilation pairs. These can only occur in open systems, not in equilibrium condensates, in contrast to well-established vortex-antivortex pairs

Turing patterns in semiconductor microcavity polaritons: theory and experiment

PosterWe study spontaneous formation of regular polariton patterns in quantum-well semiconductor microcavities for continuous-wave optical pumping. Our study is based on (i) fully two-dimensional simulations of the mean-field dynamics of the coupled cavity-field and exciton system, (ii) a simplified mode-competition model to systematically organize our results including various phase transitions, and (iii) experiments giving evidence for spontaneous hexagon formation in a coherent polariton system (cf. Fig.1). This combination allows to interpret our results both from a microscopic polariton-scattering perspective and from a more phenemenological (and general) nonlinear dynamical systems perspective. In addition to the results shown in Fig.1, we will discuss all-optical switching of polariton patterns triggered by an additional external control and relate this to transitions across phase boundaries in the simplified model. The exploration of this rich spectrum of instability behavior and phase transitions is of fundamental interest and will have implications for the development of all-optical low-intensity polariton switches [1]. [1] A. M. C. Dawes, D. J. Gauthier, S. Schumacher, N. H. Kwong, R. Binder, and A. L. Smirl, Transverse optical patterns for ultra-low-light-level all-optical switching, Laser & Photonics Reviews 4, 221 (2010)

Formation and Control of Transverse Patterns in a Quantum Fluid of Microcavity Polaritons

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