:sr]У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 25. новембра 2021. године у 14 часова путем Zoom платформе, др Томасо Макри (Департман за теоријску и експерименталну физику, Федерални универзитет у Рио Гранде до Норте, Натал, Бразил), одржаће предавање:

Solitons and polarons in ultracold bosonic mixtures

САЖЕТАК:

The realization of multicomponent systems offers a natural playground to observe nonequilibrium effects in a more general framework. Restricting to two-component BECs, one notices already a rich variety of phases in the ground state. In purely repulsive mixtures, one observes a homogeneous superfluid or a phase separation when inter-species repulsion overcomes the intra-species interaction strength. In the attractive regime a series of recent experiments showed the formation of dilute self-bound droplet states in a two-component BEC both in a tight optical waveguide and in free space, closely following the theoretical predictions. In the quasi one-dimensional geometry, upon varying the mean-field interaction from the weakly to the strongly attractive regime, one observes a smooth crossover between bright soliton states and self-bound droplets. In the first part of this talk we will investigate the quench dynamics of a two component Bose mixture and study the onset of modulational instability, which leads the system far from equilibrium. Analogous to the single-component counterpart, this phenomenon results in the creation of trains of bright solitons. In the second part we will discuss the properties of impurities in uniform and self-bound states of heteronuclear mixtures inspired by recent experiments. Finally, we will focus on the formation of exotic bound states for an impurity interacting with a self-bound droplet.

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Meeting ID: 813 8100 5164
Passcode: 667308

У оквиру семинара Групе за гравитацију, честице и поља Института за физику у Београду, у петак, 19. новембра 2021. године у 12 часова путем BigBlueButton платформе, др Воја Радовановић (Физички факултет у Београду), одржаће предавање:

Black hole entropy and the information loss paradox

САЖЕТАК:

The most important unsolved problem in black hole physics is the information loss paradox, i.e. whether the process of formation and evaporation of a black hole is unitary in accordance with quantum mechanics. The unitarity implies that von Neumann entropy of the Hawking radiation should initially increase but subsequently fall back down, following the so-called Page curve.

In the first talk of this series we consider black hole thermodynamics and discuss various concepts of entropy: fine-grained, coarse-grained and entanglement entropy. In addition, we calculate entanglement entropy for Rindler observer and show how to generalize this result to curved space-time, where it is used to define generalized entropy of a black hole.

The upcoming talks will be devoted to the so-called wormhole replica trick and the notion of an island – a kind of a quantum extremal surface recently advocated by Maldacena. We study a particular case of 2D dilaton gravity obtained by dimensional reduction of the Einstein-Hilbert action for Schwarzschild metric. We calculate the von Neumann entropy of the Hawking radiation and reproduce the Page curve.

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У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 18. новембра 2021. године у 14 часова путем Zoom платформе, др Јакша Вучичевић (Лабораторија за примену рачунара у науци, Центар за изучавање комплексних система, Институт за физику у Београду), одржаће предавање:

Universal magnetic quantum oscillations in correlated lattice systems

САЖЕТАК:

Magnetic field is well known to have drastic effects on the transport properties of electronic systems. Similar to the quantum Hall effect in continuum systems, the Shubnikov-de Haas (SdH) effect in crystalline materials is an oscillatory behavior of conductivity as a function of the applied magnetic field. This phenomenon is well understood in good metals, and has been very useful in mapping out the Fermi surface in various materials. In recent experiments on synthetic moire systems, a new type of magnetic quantum oscillations has been observed that differs from SdH oscillations in two important aspects: the so called Brown-Zak (BZ) oscillations appear at elevated temperature and have no dependence on the size of the two-dimensional Fermi sea. In this talk, we will present the dynamical mean field theory (DMFT) results for the square-lattice Hubbard model in a magnetic field that clearly display the phenomenology of the BZ oscillations [1, 2]. A detailed analysis reveals an essential role of incoherence for the BZ oscillations, which may allow one to use this phenomenon as a tool for characterization of dominant scattering mechanisms in lattice systems.

[1] J. Vučičević and R. Žitko, Phys. Rev. Lett. 127, 196601 (2021).
[2] J. Vučičević and R. Žitko, Phys. Rev. B 104, 205101 (2021).

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Meeting ID: 863 3529 3898
Passcode: 054147

У оквиру семинара Групе за гравитацију, честице и поља Института за физику у Београду, у петак,5. новембра 2021. године у 11 часова путем BigBlueButton платформе, Илија Бурић (Департман за физику, Универзитет у Пизи), одржаће предавање:

Conformal bootstrap – a non-perturbative approach to conformal field theories

САЖЕТАК:

Conformal bootstrap is a collection of methods for the study of conformal field theories, which are based on minimal assumptions such as unitarity and self-consistency. After reviewing the basic structure of conformal field theories, I will illustrate some of these methods on one numerical and one analytic example.

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У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 28. октобра 2021. године у 14 часова путем Zoom платформе, Милан Крстајић (Лабораторија Кларендон, Универзитет у Оксфорду), одржаће предавање:

Experimental platform for a box-trapped dipolar quantum gas

САЖЕТАК:

Dipolar quantum gases make up an increasingly popular branch within an already thriving field of ultracold quantum gases. The interest in such systems lies in a multitude of quantum phenomena that stem from dipole-dipole interactions, particularly from their long-range and anisotropic nature. This talk describes the design and building of an experimental platform for investigating many-body physics in homogeneous dipolar quantum gases of erbium. We will present results on the progress towards reaching the goal of an erbium Bose-Einstein condensate in an optical box potential, including the performance of laser cooling methods and the optical systems for optical trapping and transport. At present, the experiment is capable of producing clouds with 100 million atoms at the temperature of 15 microkelvin in the magneto-optical trap, which translates into about 15 million atoms at 50 microkelvin following transfer into an optical dipole trap. We will discuss details on the remaining steps to complete the platform and present an overview of the research topics our platform will make accessible, including roton physics and supersolidity, out-of-equilibrium many-body phenomena and dynamics of phase transitions in systems with long-range interactions. We will also briefly touch upon the subject of expanding the apparatus to a dual-species experiment with potassium, which will enable investigating systems with impurities. Finally, we will extend the discussion to results from numerical simulations on the stability of a purely dipolar quantum gas against collapse in a general power-law trap (of which the optical box is an example), showing that intermediate power-law traps lead to maximally homogeneous density distributions for near-critical interaction strengths.

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Meeting ID: 898 9938 6885
Passcode: 860765

У оквиру семинара Групе за гравитацију, честице и поља Института за физику у Београду, у среду, 27. октобра 2021. године у 13 часова путем BigBlueButton платформе, Волфганг Мартин Виланд (Аустријска академија наука, Институт за квантну оптику и квантну информацију, Беч), одржаће предавање:

How the Immirzi Parameter deforms the SL(2,R) Boundary Symmetries on the Light Cone

САЖЕТАК:

This talk describes how the Barbero–Immirzi parameter deforms the SL(2,R) symmetries on a null surface boundary. Our starting point is the definition of the action and its boundary terms. The action that we use is the usual Holst action. Compared to metric gravity it contains an additional coupling constant — the Barber Immirzi parameter. Given the action and the boundary conditions, we introduce the covariant phase space and explain how the Holst term alters the boundary symmetries on a null surface. This alteration only affects the algebra of the edge modes on a cross-section, whereas the algebra of the radiative modes is unchanged by the addition of the Barbero–Immirzi parameter. To compute the Poisson brackets explicitly, we work on an auxiliary phase space, where the SL(2,R) symmetries of the boundary fields are manifest. The physical phase space is obtained by imposing both first-class and second-class constraints. All gauge generators are at most quadratic in terms of the fundamental SL(2,R) variables. Finally, we discuss various strategies to quantise the system.

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У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 14. октобра 2021. године у 14 часова путем Zoom платформе, др Ива Бачић (Лабораторија за примену рачунара у науци, Центар за изучавање комплексних система, Институт за физику у Београду и Департман за науку о мрежама и подацима, Централно-европски универзитет, Будимпешта), одржаће предавање:

Onset of physicality in a random network growth model

САЖЕТАК:

Networks are abstract representations of complex systems in which any physicality of their constituents is disregarded. In a number of real networks, however, nodes and links are physical objects embedded in space that cannot intersect with each other. If the size of nodes and links is small compared to the available space, physicality likely has little effect on the network; however, if the volume of the network is comparable to volume of the available space, physicality will affect the structure, the evolution, and the function of the networks. Examples of such systems include neurons in the brain, the vascular system, mycelial networks, three-dimensional integrated circuits, and subways or other similar infrastructures. This observation prompts the question: when does physicality matter? In this talk we will propose a tractable random growth model of physical networks that provides insight into this question. The model describes linear physical networks, where links are non-overlapping straight cylinders. Network growth is achieved by sequentially adding nodes to randomly chosen points within the unit cube, and connecting to a randomly chosen accessible node from the existing network, with non-crossing conditions taken into account. We will identify two critical transitions: (i) the onset of the weakly physical regime, where the average link length becomes shorter, although the volume of the network is still negligible compared to the available volume, and (ii) the onset of the strongly physical regime, where the network occupies a finite fraction of the cube’s volume. We will demonstrate the validity of the analytical arguments by extensive numerical simulations.

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Meeting ID: 841 4527 0449
Passcode: 551996