Quantum Phase Transitions in Cold Atoms and Low Temperature Solids

Abstract

This thesis describes how to create and probe novel phases of matter and exotic (non-quasiparticle) behavior in cold atomic gases. It focuses on situations whose physics is relevant to condensed matter systems, and where open questions about these latter systems can be addressed. It also attempts to better understand several experimental anomalies in condensed matter systems.The thesis is divided into five parts. The first section or chapter of each part gives an introduction to the motivation and background for the physics of that part; the last section or chapter gives an outlook for future studies. Parts 1-4 (Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15) introduce and show different facets of how to learn about novel physics relevant to condensed matter using cold atomic systems. Part 5 ( Chapters 16, 17, 18, and 19) constrains explanations of several ill-understood phenomena occurring in low-temperature quantum solids and condensed matter systems and attempts to construct mechanisms for their behavior.Part 1 (Chapters 1 and 2) generally motivates and introduces condensed matter, cold atoms, and many-body physics. Part 2 (Chapters 3, 4, 5, 6, and 7) introduces optical lattice physics and describes ways of spectroscopically probing many-body physics, especially dynamics, near quantum phase transitions in these systems. Part 3 (Chapters 8, 9, 10, 11, and 12) discusses the effects of rotation and how this can create exotic states, as well as alternative methods of creating exotic states. This leads us to study optical lattices where particles possess non-trivial correlations between particles even within a site in Chapters 10 and 11. Part 4 (Chapters 13, 14, and 15) introduces another route to studying exotic physics in cold atoms: examining finite temperature behavior near second order quantum phase transitions. In the "quantum critical regime" occurring near these transitions, non-quasiparticle behavior generically manifests. This behavior has been hidden in previous analyses of data, but Chapter 14 introduces a set of tools required to extract universal quantum critical behavior from standard observables in cold atoms experiments. Chapter 15 discusses near-term opportunities to use these tools to impact fundamental, open questions in condensed matter physics.Part 5 (Chapters 16, 17, 18, and 19) introduces several anomalous or interesting experimental results from low-temperature and solid state physics, constrains possible explanations, and attempts to construct mechanisms for their behavior.Chapter 17 shows that collisional properties between quasi-two-dimensional spinpolarized hydrogen atoms are dramatically modified by the presence of a helium film, on which they are invariably adsorbed in present experiments. Chapter 18 constrains theories regarding recent observations on atomic hydrogen defects in molecular hydrogen quantum solids. Finally, Chapter 19 proposes a mechanism for supersolidity that could account for the experimental observations at that time.Since then, it probably has been...

Estudo teórico de transição quântica de fases em gases bosônicos aprisionados por redes ópticas periódica e quase periódica

“…Recentemente, o interesse neste modelo foi renovado graças as possibilidades teóricas [5,6] e experimentais de observar uma fase supersólida [7]. Um supersólido, ou uma fase supersólida, é o resultado de um fenômeno paradoxal em que uma substância resistente ao cisalhamento -um sólido -também apresenta comportamento característico de um superfluido [8]. Em outras palavras, o sistema se organiza em duas ordens: superfluida e sólida.…”

Quantum spin-1 anisotropic ferromagnetic Heisenberg model in a crystal field: A variational approach

“…Quantum phase transitions have been extensively studied in the literature [1][2][3][4][5][6][7] and their fully understanding is still one of the most interesting and important subjects in the modern condensed matter physics, both experimentally and theoretically. These transitions have been observed in several experimental realizations such as, for instance, the magnetic insulators LiHoF 4 8 , La 2 CuO 4 9 , and heavy-fermion systems 10 as CeRu 2 Si 2 , β-Y bAlB 4 .…”

Harnessing currents of particles for spectroscopy in small-ring lattices with binary mixtures

“…Introduction. -The characterization of many-body states is of paramount importance in the field of cold-atom physics [1][2][3]. Currently, many-body states can be experimentally analyzed using a wide number of techniques that range from momentum distribution [4], noise correlations [5,6], rf-spectroscopy [3], Bragg spectroscoy [7] and lattice modulation spectroscopy [8,9].…”

“…-The characterization of many-body states is of paramount importance in the field of cold-atom physics [1][2][3]. Currently, many-body states can be experimentally analyzed using a wide number of techniques that range from momentum distribution [4], noise correlations [5,6], rf-spectroscopy [3], Bragg spectroscoy [7] and lattice modulation spectroscopy [8,9]. This scenario becomes richer in binary mixtures [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], where the interplay between species leads to novel and exotic quantum phases [26,27].…”