10,659 research outputs found
Quantum Phase Transitions in Bosonic Heteronuclear Pairing Hamiltonians
We explore the phase diagram of two-component bosons with Feshbach resonant
pairing interactions in an optical lattice. It has been shown in previous work
to exhibit a rich variety of phases and phase transitions, including a
paradigmatic Ising quantum phase transition within the second Mott lobe. We
discuss the evolution of the phase diagram with system parameters and relate
this to the predictions of Landau theory. We extend our exact diagonalization
studies of the one-dimensional bosonic Hamiltonian and confirm additional Ising
critical exponents for the longitudinal and transverse magnetic
susceptibilities within the second Mott lobe. The numerical results for the
ground state energy and transverse magnetization are in good agreement with
exact solutions of the Ising model in the thermodynamic limit. We also provide
details of the low-energy spectrum, as well as density fluctuations and
superfluid fractions in the grand canonical ensemble.Comment: 11 pages, 14 figures. To appear in Phys. Rev.
Hi-Val: Iterative Learning of Hierarchical Value Functions for Policy Generation
Task decomposition is effective in manifold applications where the global complexity of a problem makes planning and decision-making too demanding. This is true, for example, in high-dimensional robotics domains, where (1) unpredictabilities and modeling limitations typically prevent the manual specification of robust behaviors, and (2) learning an action policy is challenging due to the curse of dimensionality. In this work, we borrow the concept of Hierarchical Task Networks (HTNs) to decompose the learning procedure, and we exploit Upper Confidence Tree (UCT) search to introduce HOP, a novel iterative algorithm for hierarchical optimistic planning with learned value functions. To obtain better generalization and generate policies, HOP simultaneously learns and uses action values. These are used to formalize constraints within the search space and to reduce the dimensionality of the problem. We evaluate our algorithm both on a fetching task using a simulated 7-DOF KUKA light weight arm and, on a pick and delivery task with a Pioneer robot
Feshbach Resonance in Optical Lattices and the Quantum Ising Model
Motivated by experiments on heteronuclear Feshbach resonances in Bose
mixtures, we investigate s-wave pairing of two species of bosons in an optical
lattice. The zero temperature phase diagram supports a rich array of superfluid
and Mott phases and a network of quantum critical points. This topology reveals
an underlying structure that is succinctly captured by a two-component Landau
theory. Within the second Mott lobe we establish a quantum phase transition
described by the paradigmatic longitudinal and transverse field Ising model.
This is confirmed by exact diagonalization of the 1D bosonic Hamiltonian. We
also find this transition in the homonuclear case.Comment: 5 pages, 4 figure
Assessing the Potential of Classical Q-learning in General Game Playing
After the recent groundbreaking results of AlphaGo and AlphaZero, we have
seen strong interests in deep reinforcement learning and artificial general
intelligence (AGI) in game playing. However, deep learning is
resource-intensive and the theory is not yet well developed. For small games,
simple classical table-based Q-learning might still be the algorithm of choice.
General Game Playing (GGP) provides a good testbed for reinforcement learning
to research AGI. Q-learning is one of the canonical reinforcement learning
methods, and has been used by (Banerjee Stone, IJCAI 2007) in GGP. In this
paper we implement Q-learning in GGP for three small-board games (Tic-Tac-Toe,
Connect Four, Hex)\footnote{source code: https://github.com/wh1992v/ggp-rl}, to
allow comparison to Banerjee et al.. We find that Q-learning converges to a
high win rate in GGP. For the -greedy strategy, we propose a first
enhancement, the dynamic algorithm. In addition, inspired by (Gelly
Silver, ICML 2007) we combine online search (Monte Carlo Search) to
enhance offline learning, and propose QM-learning for GGP. Both enhancements
improve the performance of classical Q-learning. In this work, GGP allows us to
show, if augmented by appropriate enhancements, that classical table-based
Q-learning can perform well in small games.Comment: arXiv admin note: substantial text overlap with arXiv:1802.0594
Polaritons and Pairing Phenomena in Bose--Hubbard Mixtures
Motivated by recent experiments on cold atomic gases in ultra high finesse
optical cavities, we consider the problem of a two-band Bose--Hubbard model
coupled to quantum light. Photoexcitation promotes carriers between the bands
and we study the non-trivial interplay between Mott insulating behavior and
superfluidity. The model displays a global U(1) X U(1) symmetry which supports
the coexistence of Mott insulating and superfluid phases, and yields a rich
phase diagram with multicritical points. This symmetry property is shared by
several other problems of current experimental interest, including
two-component Bose gases in optical lattices, and the bosonic BEC-BCS crossover
problem for atom-molecule mixtures induced by a Feshbach resonance. We
corroborate our findings by numerical simulations.Comment: 4 pages, 3 figure
An inquiry-based learning approach to teaching information retrieval
The study of information retrieval (IR) has increased in interest and importance with the explosive growth of online information in recent years. Learning about IR within formal courses of study enables users of search engines to use
them more knowledgeably and effectively, while providing the starting point for the explorations of new researchers into novel search technologies. Although IR can be taught in a traditional manner of formal classroom instruction with students being led through the details of the subject and expected to reproduce this in assessment, the nature of IR as a topic makes it an ideal subject for inquiry-based learning approaches to teaching. In an inquiry-based learning approach students are introduced to the principles of a subject and then encouraged to develop their understanding by solving structured or open problems. Working through solutions in subsequent class discussions enables students to appreciate the availability of alternative solutions as proposed by their classmates. Following this approach students not only learn the details of IR techniques, but significantly, naturally learn to apply them in solution of problems. In doing this they not only gain an appreciation of alternative solutions to a problem, but also how to assess their relative strengths and weaknesses. Developing confidence and skills in problem solving enables student assessment to be structured around solution of problems. Thus students can be assessed on the basis of their understanding and ability to apply techniques, rather simply their skill at reciting facts. This has the additional benefit of encouraging general problem solving skills which can be of benefit in other subjects. This approach to teaching IR was successfully implemented in an undergraduate module where students were
assessed in a written examination exploring their knowledge and understanding of the principles of IR and their ability to apply them to solving problems, and a written assignment based on developing an individual research proposal
Cinema and the ‘City of the Mind’: Using Motion Pictures to Explore Human-Environment Transactions in Planning Education.
This chapter examines the pedagogical use of film in planning education, specifically
as it relates to the teaching of environmental psychology. The intersections
between film, theory, and pedagogy are important because film is herein invested
with the power to represent – and more importantly interpret and challenge – our
understandings of human-environment transactions. I further suggest that planning
students may be undereducated in the nature of these transactions and that the
medium of the motion picture – combined with the neglected body of theory
represented by environmental psychology – offers an excellent synthesis to address
this need.https://link.springer.com/chapter/10.1007%2F978-90-481-3209-6_1
Fe XVII X-ray Line Ratios for Accurate Astrophysical Plasma Diagnostics
New laboratory measurements using an Electron Beam Ion Trap (EBIT) and an
x-ray microcalorimeter are presented for the n=3 to n=2 Fe XVII emission lines
in the 15 {\AA} to 17 {\AA} range, along with new theoretical predictions for a
variety of electron energy distributions. This work improves upon our earlier
work on these lines by providing measurements at more electron impact energies
(seven values from 846 to 1185 eV), performing an in situ determination of the
x-ray window transmission, taking steps to minimize the ion impurity
concentrations, correcting the electron energies for space charge shifts, and
estimating the residual electron energy uncertainties. The results for the
3C/3D and 3s/3C line ratios are generally in agreement with the closest theory
to within 10%, and in agreement with previous measurements from an independent
group to within 20%. Better consistency between the two experimental groups is
obtained at the lowest electron energies by using theory to interpolate, taking
into account the significantly different electron energy distributions.
Evidence for resonance collision effects in the spectra is discussed.
Renormalized values for the absolute cross sections of the 3C and 3D lines are
obtained by combining previously published results, and shown to be in
agreement with the predictions of converged R-matrix theory. This work
establishes consistency between results from independent laboratories and
improves the reliability of these lines for astrophysical diagnostics. Factors
that should be taken into account for accurate diagnostics are discussed,
including electron energy distribution, polarization, absorption/scattering,
and line blends.Comment: 29 pages, including 7 figure
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