Long-lived Quantum Coherence between Macroscopically Distinct States in Superradiance

The dephasing influence of a dissipative environment reduces linear superpositions of macroscopically distinct quantum states (sometimes also called Schr\"odinger cat states) usually almost immediately to a statistical mixture. This process is called decoherence. Couplings to the environment with a certain symmetry can lead to slow decoherence. In this Letter we show that the collective coupling of a large number of two-level atoms to an electromagnetic field mode in a cavity that leads to the phenomena of superradiance has such a symmetry, at least approximately. We construct superpositions of macroscopically distinct quantum states decohering only on a classical time scale and propose an experiment in which the extraordinarily slow decoherence should be observable.Comment: 4 pages of revte

Latest ALICE results of photon and jet measurements

Highly energetic jets and photons are complementary probes for the kinematics and the topology of nuclear collisions. Jets are collimated sprays of charged and neutral particles, which are produced in the fragmentation of hard scattered partons in an early stage of the collision. While traversing the medium formed in nuclear collisions, they lose energy and therefore carry information about the interaction of partons with the medium. The jet substructure is particularly interesting to learn about in-medium modification of the jets and several observables exists to probe it. In contrast to jets, photons are created in all collision stages. There are prompt photons from the initial collision, thermal photons produced in the medium, and decay- and fragmentation photons from later collision stages. Photons escape the medium essentially unaffected after their creation. This article presents recent ALICE results on jet substructure and direct photon measurements in pp, p-Pb and Pb-Pb collisions.Comment: 4 pages, 7 figures, Rencontres de Moriond proceeding

Measurement of inclusive jet spectra in pp, p-Pb, and Pb-Pb collisions with the ALICE detector

Highly energetic jets are sensitive probes for the kinematic properties and the topology of high energy hadron collisions. Jets are collimated sprays of charged and neutral particles, which are produced in fragmentation of hard scattered partons from an early stage of the collision. In ALICE, jets have been measured in pp, p-Pb, and Pb-Pb collisions at several collision energies. While analyses of Pb-Pb events unveil properties of the hot and dense medium formed in heavy-ion collisions, pp and p-Pb collisions can shed light on hadronization and cold nuclear matter effects in jet production. Additionally, pp and p-Pb serve as a baseline for disentangling hot and cold nuclear matter effects. A possible modification of the initial state is tested in p-Pb analyses. For the extraction of a jet signal, the exact evaluation of the background from the underlying event is an especially important ingredient. Due to the different nature of underlying events, each collision system requires a different analysis technique for removing the effect of the background on the jet sample. The focus of this publication is on the ALICE measurements of nuclear modification factors connecting p-Pb and Pb-Pb events to pp collisions. Furthermore, the radial jet structure is explored by comparing jet spectra reconstructed with different resolution parameters.Comment: 6 pages, 9 figures, HPT2014 proceeding

Machine and deep learning techniques in heavy-ion collisions with ALICE

Over the last years, machine learning tools have been successfully applied to a wealth of problems in high-energy physics. A typical example is the classification of physics objects. Supervised machine learning methods allow for significant improvements in classification problems by taking into account observable correlations and by learning the optimal selection from examples, e.g. from Monte Carlo simulations. Even more promising is the usage of deep learning techniques. Methods like deep convolutional networks might be able to catch features from low-level parameters that are not exploited by default cut-based methods. These ideas could be particularly beneficial for measurements in heavy-ion collisions, because of the very large multiplicities. Indeed, machine learning methods potentially perform much better in systems with a large number of degrees of freedom compared to cut-based methods. Moreover, many key heavy-ion observables are most interesting at low transverse momentum where the underlying event is dominant and the signal-to-noise ratio is quite low. In this work, recent developments of machine- and deep learning applications in heavy-ion collisions with ALICE will be presented, with focus on a deep learning-based b-jet tagging approach and the measurement of low-mass dielectrons. While the b-jet tagger is based on a mixture of shallow fully-connected and deep convolutional networks, the low-mass dielectron measurement uses gradient boosting and shallow neural networks. Both methods are very promising compared to default cut-based methods.Comment: 7 pages, 5 figures, EPS HEP 2017 proceeding

Centrality dependence of charged jets in p-Pb collisions at sNN=5.02\sqrt{s_\mathrm{NN}} = 5.02 TeV measured with the ALICE detector

Highly energetic jets are sensitive probes for the kinematics and the topology of nuclear collisions. Jets are collimated sprays of charged and neutral particles, which are produced in the fragmentation of hard scattered partons in an early stage of the collision. The measurement of jet spectra in p-Pb collisions provides an important way of quantifying the effects of cold nuclear matter in the initial state on jet production, fragmentation, and hadronization. Unlike in Pb-Pb collisions, strong hot nuclear matter effects - e.g. from quark-gluon plasma formation - are not expected to occur in p-Pb collisions. Hence, cold nuclear matter effects can be investigated in isolation. The impact of cold nuclear matter effects on charged jet spectra is expected to depend on the event centrality. Higher event centralities are principally connected to a higher probability for an interaction of proton and lead-nucleus and therefore also for a possible nuclear modification. This article is the conference proceeding of a talk, in which centrality-dependent properties of charged jets in p-Pb measured by ALICE were shown for the first time. The focus is here on the fully corrected jet production cross sections and the nuclear modification factors. Additionally, the jet radial structure is explored by comparing jet spectra reconstructed with different resolution parameters.Comment: 8 pages, 4 figures, Bormio2015 proceeding

Two support results for the Kalai-Smorodinsky solution in small object division markets

Haake C-J. Two support results for the Kalai-Smorodinsky solution in small object division markets. Working Papers. Institute of Mathematical Economics. Vol 366. Bielefeld: Universität Bielefeld; 2005.We discuss two support results for the Kalai-Smorodinsky bargaining solution in the context of an object division problem involving two agents. Allocations of objects resulting from strategic interaction are obtained as a demand vector in a specific market. For the first support result games in strategic form are derived that exhibit a unique Nash equilibrium. The second result uses subgame perfect equlibria of a game in extensive form. Although there may be multiple equilibria, coordination problems can be removed

Two support results for the Kalai-Smorodinsky solution in small object division markets

We discuss two support results for the Kalai-Smorodinsky bargaining solution in the context of an object division problem involving two agents. Allocations of objects resulting from strategic interaction are obtained as a demand vector in a specific market. For the first support result games in strategic form are derived that exhibit a unique Nash equilibrium. The second result uses subgame perfect equilibria of a game in extensive form. Although there may be multiple equilibria, coordination problems can be removed.support result, object division, market, Kalai-Smorodinsky solution