107 research outputs found
Phase transitions in three-dimensional topological lattice models with surface anyons
We study the phase diagrams of a family of 3D "Walker-Wang" type lattice
models, which are not topologically ordered but have deconfined anyonic
excitations confined to their surfaces. We add a perturbation (analogous to
that which drives the confining transition in Z_p lattice gauge theories) to
the Walker-Wang Hamiltonians, driving a transition in which all or some of the
variables associated with the loop gas or string-net ground states of these
models become confined. We show that in many cases the location and nature of
the phase transitions involved is exactly that of a generalized Z_p lattice
gauge theory, and use this to deduce the basic structure of the phase diagram.
We further show that the relationship between the phases on opposite sides of
the transition is fundamentally different than in conventional gauge theories:
in the Walker-Wang case, the number of species of excitations that are
deconfined in the bulk can increase across a transition that confines only some
of the species of loops or string-nets. The analogue of the confining
transition in the Walker-Wang models can therefore lead to bulk deconfinement
and topological order
Three-dimensional topological lattice models with surface anyons
We study a class of three dimensional exactly solvable models of topological
matter first put forward by Walker and Wang [arXiv:1104.2632v2]. While these
are not models of interacting fermions, they may well capture the topological
behavior of some strongly correlated systems. In this work we give a full
pedagogical treatment of a special simple case of these models, which we call
the 3D semion model: We calculate its ground state degeneracies for a variety
of boundary conditions, and classify its low-lying excitations. While point
defects in the bulk are confined in pairs connected by energetic strings, the
surface excitations are more interesting: the model has deconfined point
defects pinned to the boundary of the lattice, and these exhibit semionic
braiding statistics. The surface physics is reminiscent of a bosonic
fractional quantum Hall effect in its topological limit, and these
considerations help motivate an effective field theoretic description for the
lattice models as variants of theories. Our special example of the 3D
semion model captures much of the behavior of more general `confined
Walker-Wang models'. We contrast the 3D semion model with the closely related
3D version of the toric code (a lattice gauge theory) which has deconfined
point excitations in the bulk and we discuss how more general models may have
some confined and some deconfined excitations. Having seen that there exist
lattice models whose surfaces have the same topological order as a bosonic
fractional quantum Hall effect on a confining bulk, we construct a lattice
model whose surface has similar topological order to a fermionic quantum hall
effect. We find that in these models a fermion is always deconfined in the
three dimensional bulk
Адаптация персонала организации на примере сети кафе «Пельмени Project»
Объектом исследования является–система адаптации персонала в кафе «Пельмени Project» и разработка путей ее совершенствования.
Предметом исследования является – система адаптации персонала.
Цель работы– оценка системы адаптации и разработка методов ее совершенствования в кафе «Пельмени Project». В процессе исследования проводился комплексный опрос. В результате исследования были разработаны рекомендации по улучшению системы адаптации персоналом в кафе «Пельмени Project».
Степень внедрения:система адаптации молодых сотрудников в кафе
«Пельмени Project» находится на хорошем уровне, проводятся различные мероприятия для благоприятной адаптации на работе, несмотря на это, все равно существует ряд недоработок в этой области, подтверждением тому является текучка кадров и неудовлетворенность новых сотрудников.The object of this study is to adapt the system-staff in the cafe "Dumplings Project» and to develop ways to improve it. The subject issledovaniyayavlyaetsya - personnel system adaptation.
The purpose work- evaluation system to adapt and develop methods to improve it in the cafe "Dumplings Project». The study conducted a comprehensive survey. The study developed recommendations to improve the personnel system to adapt to the cafe "Dumplings Project».
Degree of implementation: adapting the system of young staff in the cafe
"Dumplings Project» is at a good level, hosts a variety of
supportive measures for adaptation to work, in spite of this, all
still there are some shortcomings in this area, confirming that
is staff turnover and dissatisfaction with the new employees
Observation of discrete time-crystalline order in a disordered dipolar many-body system
Understanding quantum dynamics away from equilibrium is an outstanding
challenge in the modern physical sciences. It is well known that
out-of-equilibrium systems can display a rich array of phenomena, ranging from
self-organized synchronization to dynamical phase transitions. More recently,
advances in the controlled manipulation of isolated many-body systems have
enabled detailed studies of non-equilibrium phases in strongly interacting
quantum matter. As a particularly striking example, the interplay of periodic
driving, disorder, and strong interactions has recently been predicted to
result in exotic "time-crystalline" phases, which spontaneously break the
discrete time-translation symmetry of the underlying drive. Here, we report the
experimental observation of such discrete time-crystalline order in a driven,
disordered ensemble of dipolar spin impurities in diamond at
room-temperature. We observe long-lived temporal correlations at integer
multiples of the fundamental driving period, experimentally identify the phase
boundary and find that the temporal order is protected by strong interactions;
this order is remarkably stable against perturbations, even in the presence of
slow thermalization. Our work opens the door to exploring dynamical phases of
matter and controlling interacting, disordered many-body systems.Comment: 6 + 3 pages, 4 figure
Distribution and consequences of VKORC1 polymorphisms in Germany
Runge, M., Von Keyserlingk, M., Braune, S., Freise, J., Eiler, T., Plenge-Bönig, A., Becker, D., Pelz, H.-J., Esther, A., Rost, S., Müller, C.R
Periodically driving a many-body localized quantum system
We experimentally study a periodically driven many-body localized system
realized by interacting fermions in a one-dimensional quasi-disordered optical
lattice. By preparing the system in a far-from-equilibrium state and monitoring
the remains of an imprinted density pattern, we identify a localized phase at
high drive frequencies and an ergodic phase at low ones. These two distinct
phases are separated by a dynamical phase transition which depends on both the
drive frequency and the drive strength. Our observations are quantitatively
supported by numerical simulations and are directly connected to the change in
the statistical properties of the effective Floquet Hamiltonian.We acknowledge support from Technical University of Munich - Institute for Advanced Study, funded by the German Excellence Initiative and the European Union FP7 under grant agreement 291763, from the DFG grant no. KN 1254/1-1, the European Commission (UQUAM, AQuS) and the Nanosystems Initiative Munich (NIM)
Recommended from our members
Effects of degree and timing of social housing on reversal learning and response to novel objects in dairy calves
Rodents and primates deprived of early social contact exhibit deficits in learning and behavioural
flexibility. They often also exhibit apparent signs of elevated anxiety, although the relationship between these effects has not been studied. To investigate whether dairy calves are similarly affected, we first compared calves housed in standard individual pens
(n = 7) to those housed in a dynamic group with access to their mothers (n = 8). All calves learned to approach the correct stimulus in a visual discrimination task. Only one individually housed calf was able to re-learn the task when the stimuli were reversed, compared to all but one calf from the group. A second experiment investigated whether this effect might be explained by anxiety in individually housed animals interfering with their learning, and tested varying degrees of social contact in addition to the complex group: pair housing beginning early (approximately 6 days old) and late (6 weeks old). Again, fewer individually reared calves learned the reversal task (2 of 10 or 20%) compared to early paired and grouped calves (16 of 21 or 76% of calves). Late paired calves had intermediate success. Individually housed calves were slower to touch novel objects, but the magnitude of the fear response did not correlate with reversal performance. We conclude that individually housed calves have learning deficits, but these deficits were not likely associated with increased
anxiety
Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases
We analyze the properties of a single impurity immersed in a Fermi sea. At
positive energy and scattering lengths, we show that the system possesses a
well-defined but metastable excitation, the repulsive polaron, and we calculate
its energy, quasiparticle residue and effective mass. From a thermodynamic
argument we obtain the number of particles in the dressing cloud, illustrating
the repulsive character of the polaron. Identifying the important 2- and 3-body
decay channels, we furthermore calculate the lifetime of the repulsive polaron.
The stability conditions for the formation of fully spin polarized
(ferromagnetic) domains are then examined for a binary mixture of atoms with a
general mass ratio. Our results indicate that mass imbalance lowers the
critical interaction strength for phase-separation, but that very short
quasiparticle decay times will complicate the experimental observation of
itinerant ferromagnetism. Finally, we present the spectral function of the
impurity for various coupling strengths and momenta.Comment: Substantial improvements to the section describing quasiparticle
decays (included a discussion of two-body and three-body processes), and to
the criteria for the stability of the itinerant ferromagnetic phas
R\ue9nyi entropies of generic thermodynamic macrostates in integrable systems
We study the behaviour of R\ue9nyi entropies in a generic thermodynamic macrostate of an integrable model. In the standard quench action approach to quench dynamics, the R\ue9nyi entropies may be derived from the overlaps of the initial state with Bethe eigenstates. These overlaps fix the driving term in the thermodynamic Bethe ansatz (TBA) formalism. We show that this driving term can be also reconstructed starting from the macrostate's particle densities. We then compute explicitly the stationary R\ue9nyi entropies after the quench from the dimer and the tilted N\ue9el state in XXZ spin chains. For the former state we employ the overlap TBA approach, while for the latter we reconstruct the driving terms from the macrostate. We discuss in full detail the limits that can be analytically handled and we use numerical simulations to check our results against the large time limit of the entanglement entropies
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