Excited-State Quantum Phase Transitions in Bosonic Lattice Systems

Concentrating on bosonic lattice systems, we ask whether and how Excited State Quantum Phase Transition (ESQPT) singularities occur in condensed matter systems with ground state QPTs. We study in particular the spectral singularities above the ground-state phase diagram of the boson Hubbard model. As a general prerequisite, we point out the analogy between ESQPTs and van Hove singularities (vHss).Comment: 3 pages, 2 figures, to appear in AIP Conference Proceedings, Symmetries And Order: Algebraic Methods In Many Body Systems, In honor of Professor Francesco Iachello on the occasion of his retirement, October 5-6, 2018 at Yale University (v2 minor reformulations

Excited-state quantum phase transitions in systems with two degrees of freedom: III. Interacting boson systems

The series of articles [Ann. Phys. 345, 73 (2014) and 356, 57 (2015)] devoted to excited-state quantum phase transitions (ESQPTs) in systems with $f=2$ degrees of freedom is continued by studying the interacting boson model of nuclear collective dynamics as an example of a truly many-body system. The intrinsic Hamiltonian formalism with angular momentum fixed to $L=0$ is used to produce a generic first-order ground-state quantum phase transition with an adjustable energy barrier between the competing equilibrium configurations. The associated ESQPTs are shown to result from various classical stationary points of the model Hamiltonian, whose analysis is more complex than in previous cases because of (i) a non-trivial decomposition to kinetic and potential energy terms and (ii) the boundedness of the associated classical phase space. Finite-size effects resulting from a partial separability of both degrees of freedom are analyzed. The features studied here are inherent in a great majority of interacting boson systems.Comment: 14 pages, 6 figure

Excited-state quantum phase transitions

We review the effects of excited-state quantum phase transitions (ESQPTs) in interacting many-body systems with finite numbers of collective degrees of freedom. We classify typical ESQPT signatures in the spectra of energy eigenstates with respect to the underlying classical dynamics and outline a variety of quantum systems in which they occur. We describe thermodynamic and dynamic consequences of ESQPTs, like those in microcanonical thermodynamics, quantum quench dynamics, and in the response to nearly adiabatic or periodic driving. We hint at some generalizations of the ESQPT concept in periodic lattices and in resonant tunneling systems.Comment: 78 pages, 21 figures, review articl

Coulomb analogy for nonhermitian degeneracies near quantum phase transitions

Degeneracies near the real axis in a complex-extended parameter space of a hermitian Hamiltonian are studied. We present a method to measure distributions of such degeneracies on the Riemann sheet of a selected level and apply it in classification of quantum phase transitions. The degeneracies are shown to behave similarly as complex zeros of a partition function.Comment: 4 page

Mobile applications development for remote control of instrumentation

Předkládaná práce popisuje rozšiřující se trend využívající mobilní zařízení k ovládání laboratorních přístrojů a zobrazování naměřených dat. Hlavním cílem je vývoj aplikace pro mobilní zařízení, díky které bude možné vzdáleně ovládat a měřit s přístroji v laboratoři. Praktická část je zaměřena na naprogramování mobilní aplikace, která s využitím místní sítě bude schopna připojit se k více laboratorním zařízením, nastavit je pro různé druhy měření a následně zobrazit naměřená data.The presented work describes the growing trend of using mobile devices to control laboratory instruments and displaying of measured data. The main objective is the application development for mobile devices, which will allow to remotely control and measure with laboratory instruments. The practical part is focused to programming mobile application which will be able by using the local network to connect multiple laboratory instruments, setting them for different types of measurements and then display measured data.