magistrsko delo
Gregor Humar (Author), Dragan Mihailović (Mentor), Jaka Vodeb (Co-mentor)

Abstract

V tej magistrski nalogi obravnavamo razpad lažnega vakuuma v Isingovem modelu s transverzalnim poljem z metodo kvantnega žarjenja. Razpad lažnega vakuuma je ena izmed osrednjih idej v kvantni teoriji polja. Opisuje primer, v katerem sistem v metastabilnem stanju lažnega vakuuma preide v stanje pravega vakuuma. Prehod se zgodi z nastankom mehurčkov pravega vakuuma, ki se nato razširijo čez celoten sistem. Časovne skale in dinamiko tega pojava pa je težko opazovati in opisati analitično. Proces prehoda je analogen faznemu prehodu prvega reda v fiziki kondenzirane snovi. Metastabilne sisteme z analogno dinamiko lahko opazujemo na časovnih skalah, ki omogočajo meritve, primer takega sistema je Isingov model s transverzalnim poljem. Razpad lažnega vakuuma se pojavi v neravnovesni dinamiki tega sistema, ki sledi nenadni menjavi smeri zunanjega polja. Študije z numeričnimi metodami so pokazale, da obstaja omejen nabor parametrov, za katere je možno opazovati razpad lažnega vakuuma. Isingov model s transverzalnim poljem pa je implementiran v D-Wave kvantnem žarilniku. Meritve na tej napravi uporabimo za simulacije dinamike Isingovega modela s transverzalnim poljem. Rezultati simulacij v splošnem pokažejo razpadno dinamiko, ki se ne sklada popolnoma s teoretičnim opisom razpada lažnega vakuuma, kar kaže na druge vplive na dinamiko. V specifični limiti nizkih transverzalnih polj in visokih longitudinalnih polj pa se izmerjena dinamika približa pričakovani teoretični dinamiki. Možne razlage za izmerjena odstopanja vključujejo odprto naravo sistema v kvantnem žarilniku, počasno spreminjanje smeri polja in slabo veljavnost približkov, uporabljenih za teoretične izračune, za velikosti polj pri katerih opazujemo razpad.

Keywords

vakuum;razpad lažnega vakuuma;metastabilna stanja;kvantno tuneliranje;Isingov model;spinske verige;kvantno žarjenje;neravnovesna dinamika;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [G. Humar]
UDC: 530.145
COBISS: 164471043 Link will open in a new window
Views: 12
Downloads: 4
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Other data

Secondary language: English
Secondary title: False vacuum decay in the transverse field Ising model on a quantum annealer
Secondary abstract: This master thesis deals with using quantum annealing for observing false vacuum decay in the transverse field Ising model. False vacuum decay is one of the central ideas in quantum field theory. It describes a scenario where a system in a metastable false vacuum state transitions to the true vacuum state. The transition happens by creation of bubbles of true vacuum that expand over the whole system. The timescales and the dynamics of this phenomenon are difficult to observe and describe analytically. The process of transition is analogue to first order phase transitions in condensed matter physics. Metastable states with analogous dynamics can be observed on measurable timescales. An example of such a system is the transverse field Ising model, where false vacuum decay appears in nonequilibrium dynamics following a sudden change in the direction of the external field. Numerical studies have shown the existance of a set of parameters for which false vacuum decay can be observed. Transverse field Ising model is implemented in the D-Wave quantum annealer. Measurements on this device are used to simulate the dynamics of the transverse Ising model. In general, results of simulations show decay dynamics that do not match the theoretical description of the false vacuum decay exactly. This implies additions effects on the dynamics. In the specific limit of low transverse fields and high longitudinal fields the measured dynamics approach the theoretically expected dynamics. Possible explanations for the observed deviations include the open nature of the system in the quantum annealer, the slow change of the field direction and poor validity of the approximations used for theoretical predictions for magnitudes of fields used in the simulations.
Secondary keywords: vacuum;false vacuum decay;metastable states;quantum tunneling;Ising model;spin chains;quantum annealing;nonequilibrium dynamics;
Type (COBISS): Master's thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 54 str.
ID: 19937474