Quantum Cloning of Binary Coherent States - Optimal Transformations and Practical Limits

The notions of qubits and coherent states correspond to different physical systems and are described by specific formalisms. Qubits are associated with a two-dimensional Hilbert space and can be illustrated on the Bloch sphere. In contrast, the underlying Hilbert space of coherent states is infinite-dimensional and the states are typically represented in phase space. For the particular case of binary coherent state alphabets these otherwise distinct formalisms can equally be applied. We capitalize this formal connection to analyse the properties of optimally cloned binary coherent states. Several practical and near-optimal cloning schemes are discussed and the associated fidelities are compared to the performance of the optimal cloner.Comment: 12 pages, 12 figure

Lift force acting on an intruder in dense, granular shear flows

We report a new lift force model for intruders in dense, granular shear flows. Our derivation is based on the thermal buoyancy model of Trujillo & Hermann[L. Trujillo and H. J. Herrmann, Physica A 330, 519 (2003).], but takes into account both granular temperature and pressure differences in the derivation of the net buoyancy force acting on the intruder. In a second step the model is extended to take into account also density differences between the intruder and the bed particles. The model predicts very well the rising and sinking of intruders, the lift force acting on intruders as determined by discrete element model (DEM) simulations and the neutral-buoyancy limit of intruders in shear flows. Phenomenologically, we observe a cooling upon the introduction of an intruder into the system. This cooling effect increases with intruder size and explains the sinking of large intruders. On the other hand, the introduction of small to mid-sized intruders, i.e. up to 4 times the bed particle size, leads to a reduction in the granular pressure compared to the hydrostatic pressure, which in turn causes the rising of small to mid-sized intruders.Comment: 13 page

QPSK coherent state discrimination via a hybrid receiver

We propose and experimentally demonstrate a near-optimal discrimination scheme for the quadrature phase shift keying protocol (QPSK). We show in theory that the performance of our hybrid scheme is superior to the standard scheme - heterodyne detection - for all signal amplitudes and underpin the predictions with our experimental results. Furthermore, our scheme provides the hitherto best performance in the domain of highly attenuated signals. The discrimination is composed of a quadrature measurement, a conditional displacement and a threshold detector

Probabilistic Cloning of Coherent States without a Phase Reference

We present a probabilistic cloning scheme operating independently of any phase reference. The scheme is based solely on a phase-randomized displacement and photon counting, omitting the need for non-classical resources and non-linear materials. In an experimental implementation, we employ the scheme to clone coherent states from a phase covariant alphabet and demonstrate that the cloner is capable of outperforming the hitherto best-performing deterministic scheme. An analysis of the covariances between the output states shows that uncorrelated clones can be approached asymptotically. An intriguing feature is that the trade-off between success rate and achieved fidelity can be optimized even after the cloning procedure

Reversal of gulf stream circulation in a vertically vibrated triangular fluidized bed

Proceeding of: Fifteenth International Conference on Fluidization, Fluidization XV, Fluidization for Emerging Green Technologies, Montebello, Canada, May 22nd to 27th, 2016The present work experimentally assesses the effect of vibration on the dynamics of particles in a fluidized bed of triangular shape. The base of the bed is composed of two inclined walls, each one forming an angle of 45 with the horizontal. The bed has 0.206 m span and 0.01 m thickness. The bed vessel is made of antistatic PMMA in order to allow optical access with a high-speed camera. The bed is mounted on an electrodynamic shaker which produces vertical vibration. The bed material is ballotini particles with a mean diameter of 1.15 mm up to the top of the inclined walls. Air was injected through the inclined bed walls to fluidize the bed to explore whether vibration of the bed vessel together with gas injection can make the dynamics of this bed different to that found when no gas is injected. A high speed camera was used to record the motion of particles in the bed. The velocity of the particles in the bed was obtained via Particle Image Velocimetry (PIV). The results show that several circulation patterns are observed as a function of vibration amplitude and frequency when the fluidization velocity is just below and above the minimum fluidization velocity. Noticeably, for zero gas velocity, particles ascend close to the side walls and descend in the center of the bed. By injecting fluidization gas, the circulation pattern of the bed can be reversed (i.e. particles descending near the inclined walls and ascending in the center of the bed). Conditions for which this reversal of the gulf stream circulation of particles appears in the triangular bed are explored in this work and these include gas superficial velocities higher than the minimum fluidization velocity and sufficiently high values of the vibration strength.This work has been partially funded by the Universidad Carlos IIIde Madrid (Ayudas a la movilidad 2015) and by the Spanish Ministry of Economy and Competitiveness (project ENE2015/00188/001)