Simulation of quantum random walks using interference of classical field

We suggest a theoretical scheme for the simulation of quantum random walks on a line using beam splitters, phase shifters and photodetectors. Our model enables us to simulate a quantum random walk with use of the wave nature of classical light fields. Furthermore, the proposed set-up allows the analysis of the effects of decoherence. The transition from a pure mean photon-number distribution to a classical one is studied varying the decoherence parameters.Comment: extensively revised version; title changed; to appear on Phys. Rev.

Continuous-variable quantum teleportation of entanglement

Entangled coherent states can be used to determine the entanglement fidelity for a device that is designed to teleport coherent states. This entanglement fidelity is universal, in that the calculation is independent of the use of entangled coherent states and applies generally to the teleportation of entanglement using coherent states. The average fidelity is shown to be a poor indicator of the capability of teleporting entanglement; i.e., very high average fidelity for the quantum teleportation apparatus can still result in low entanglement fidelity for one mode of the two-mode entangled coherent state.Comment: 5 pages, 1 figure, published versio

Entanglement in bipartite generalized coherent states

Entanglement in a class of bipartite generalized coherent states is discussed. It is shown that a positive parameter can be associated with the bipartite generalized coherent states so that the states with equal value for the parameter are of equal entanglement. It is shown that the maximum possible entanglement of 1 bit is attained if the positive parameter equals $\sqrt{2}$. The result that the entanglement is one bit when the relative phase between the composing states is $\pi$ in bipartite coherent states is shown to be true for the class of bipartite generalized coherent states considered.Comment: 10 pages, 4 figures; typos corrected and figures redrawn for better clarit

Phenomenology of Mixed Modulus-Anomaly Mediation in Fluxed String Compactifications and Brane Models

In some string compactifications, for instance the recently proposed KKLT set-up, light moduli are stabilized by nonperturbative effects at supersymmetric AdS vacuum which is lifted to a dS vacuum by supersymmetry breaking uplifting potential. In such models, soft supersymmetry breaking terms are determined by a specific mixed modulus-anomaly mediation in which the two mediations typically give comparable contributions to soft parameters. Similar pattern of soft terms can arise also in brane models to stabilize the radion by nonperturbative effects. We examine some phenomenological consequences of this mixed modulus-anomaly mediation, including the pattern of low energy sparticle spectrum and the possibility of electroweak symmetry breaking. It is noted that adding the anomaly-mediated contributions at $M_{GUT}$ amounts to replacing the messenger scale of the modulus mediation by a mirage messenger scale $(m_{3/2}/M_{Pl})^{\alpha/2}M_{GUT}$ where $\alpha=m_{3/2}/[M_0\ln(M_{Pl}/m_{3/2})]$ for $M_0$ denoting the modulus-mediated contribution to the gaugino mass at $M_{GUT}$. The minimal KKLT set-up predicts $\alpha=1$. As a consequence, for $\alpha={\cal O}(1)$, the model can lead to a highly distinctive pattern of sparticle masses at TeV scale, particularly when $\alpha= 2$.Comment: 20 pages, 15 figures, some notations are changed, typos are corrected and discussions on the CP phase from $\mu$ and B are adde

The project of a high-power FEL driven by an SC ERL at KAERI

The project of a high-power FEL at Korea Atomic Energy Research Institute and its recent status are described. The FEL is driven by a superconducting energy recovery linac. The first-stage machine will operate in the far IR region and its CW power is expected to be a few kW. Possible upgrade of the machine is also considered. The upgraded machine will operate in the near IR region and its expected power is a few tens kW.Описан проект мощного ЛСЭ в Корейском институте атомной энергии, а также текущее состояние дел. В ЛСЭ будет использован сверхпроводящий линак-рекуператор. Машина первой очереди будет работать в дальнем ИК-диапазоне, ее ожидаемая средняя мощность несколько киловатт. Рассматривается возможная модернизация машины. Модернизированная машина будет генерировать десятки киловатт средней мощности в ближнем ИК-диапазоне.Описано проект потужного ЛВЕ в Корейському інституті атомної енергії, а також поточний стан справ. У ЛВЕ буде використаний надпровідний лінак-рекуператор. Машина першої черги буде працювати в далекому ІЧ-діапазоні, її очікувана середня потужність − кілька кіловат. Розглядається можлива модернізація машини. Модернізована машина буде генерувати десятки кіловатів середньої потужності в ближньому ІЧ-діапазоні

The project of a high-power FEL driven by an SC ERL at KAERI

The project of a high-power FEL at Korea Atomic Energy Research Institute and its recent status are described. The FEL is driven by a superconducting energy recovery linac. The first-stage machine will operate in the far IR region and its CW power is expected to be a few kW. Possible upgrade of the machine is also considered. The upgraded machine will operate in the near IR region and its expected power is a few tens kW.Описан проект мощного ЛСЭ в Корейском институте атомной энергии, а также текущее состояние дел. В ЛСЭ будет использован сверхпроводящий линак-рекуператор. Машина первой очереди будет работать в дальнем ИК-диапазоне, ее ожидаемая средняя мощность несколько киловатт. Рассматривается возможная модернизация машины. Модернизированная машина будет генерировать десятки киловатт средней мощности в ближнем ИК-диапазоне.Описано проект потужного ЛВЕ в Корейському інституті атомної енергії, а також поточний стан справ. У ЛВЕ буде використаний надпровідний лінак-рекуператор. Машина першої черги буде працювати в далекому ІЧ-діапазоні, її очікувана середня потужність − кілька кіловат. Розглядається можлива модернізація машини. Модернізована машина буде генерувати десятки кіловатів середньої потужності в ближньому ІЧ-діапазоні

Generation of entangled coherent states via cross phase modulation in a double electromagnetically induced transparency regime

The generation of an entangled coherent state is one of the most important ingredients of quantum information processing using coherent states. Recently, numerous schemes to achieve this task have been proposed. In order to generate travelling-wave entangled coherent states, cross phase modulation, optimized by optical Kerr effect enhancement in a dense medium in an electromagnetically induced transparency (EIT) regime, seems to be very promising. In this scenario, we propose a fully quantized model of a double-EIT scheme recently proposed [D. Petrosyan and G. Kurizki, {\sl Phys. Rev. A} {\bf 65}, 33833 (2002)]: the quantization step is performed adopting a fully Hamiltonian approach. This allows us to write effective equations of motion for two interacting quantum fields of light that show how the dynamics of one field depends on the photon-number operator of the other. The preparation of a Schr\"odinger cat state, which is a superposition of two distinct coherent states, is briefly exposed. This is based on non-linear interaction via double-EIT of two light fields (initially prepared in coherent states) and on a detection step performed using a $50:50$ beam splitter and two photodetectors. In order to show the entanglement of a generated entangled coherent state, we suggest to measure the joint quadrature variance of the field. We show that the entangled coherent states satisfy the sufficient condition for entanglement based on quadrature variance measurement. We also show how robust our scheme is against a low detection efficiency of homodyne detectors.Comment: 15 pages, 9 figures; extensively revised version; added Section

Mathematical Model of the Oxidation of a Uranium Carbide Fuel Pellet Including an Adherent Product Layer

Uranium carbide is a candidate fuel for Generation IV nuclear reactors. However, like any candidate fuel, a reprocessing route should be established before implementation. One proposed method involves a pre-oxidation step, where the carbide fuel is oxidised to an oxide and then reprocessed as normal. A mathematical model has been developed to simulate such an oxidation using finite difference approximations of the heat and mass transfer processes occurring. Available literature was consulted to provide coefficients for the reaction rates and importantly the diffusion of oxygen through the adherent oxide layer that forms on the carbide: the rate limiting step. The transient temperature, oxygen and carbon monoxide distributions through the system are modelled in order to predict oxidation completion times and the temperatures reached. It was found that for a spherical pellet of radius 0.935cm, the oxidation can take between 1 h to 19 h depending on the oxidation conditions and reach temperatures of up to 1556°C. A robust model results that offers increased understanding of a process crucial to the sustainable use of carbide fuels in energy generation

Advances in high power short pulse fiber laser systems and technology

We review recent advances in Yb fiber lasers and amplifiers for high power short pulse systems. We go on to describe associated recent developments in fiber components for use in such systems. Examples include microstructured optical fibers for pulse compression and supercontinuum generation, and advanced fiber grating technology for chirped-pulse amplifier systems

Multiorder coherent Raman scattering of a quantum probe field

We study the multiorder coherent Raman scattering of a quantum probe field in a far-off-resonance medium with a prepared coherence. Under the conditions of negligible dispersion and limited bandwidth, we derive a Bessel-function solution for the sideband field operators. We analytically and numerically calculate various quantum statistical characteristics of the sideband fields. We show that the multiorder coherent Raman process can replicate the statistical properties of a single-mode quantum probe field into a broad comb of generated Raman sidebands. We also study the mixing and modulation of photon statistical properties in the case of two-mode input. We show that the prepared Raman coherence and the medium length can be used as control parameters to switch a sideband field from one type of photon statistics to another type, or from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.