Non-equilibrium Phases of Matter in a Cavity
諧振腔中非平衡物態的研究
Student thesis: Doctoral Thesis
Author(s)
Related Research Unit(s)
Detail(s)
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| Award date | 19 Sept 2024 |
Link(s)
| Permanent Link | https://scholars.cityu.edu.hk/en/theses/theses(94a1122f-ce01-4c8b-a19a-6441a2c3dccb).html |
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| Other link(s) | Links |
Abstract
Quantum thermalization states that a non-equilibrium initial state of an isolated quantum many-body system will reach thermal equilibrium after a long time unitary evolution, and the information of the initial state is hidden, the mechanics of which are explained by the eigenstate thermalization hypothesis (ETH). However, scientists have found non-equilibrium phases of matter that avoid thermalization. Thus, some information about the initial state is maintained. This thesis focuses on a one-dimensional spin chain in a cavity, investigating two non-equilibrium phases of matter in this model, including many-body localization (MBL) and Floquet prethermalization.
In Chapter 1, I introduce the concept of thermalization in isolated quantum systems, along with the entanglement and spectral properties of thermalization. I also discuss the many-body localization (MBL) phase, which breaks down ETH by inducing a strong disorder, a phenomenon confirmed by theoretical and experimental work. Furthermore, I introduce Floquet prethermalization, which can be established without the need for disorder.
In Chapter 2, I explore the MBL of a quantum system coupled with photons. Although coupled with photons, the entanglement entropy and spectral form factor show the possible existence of finite-size MBL in the spin chain system. Additionally, I investigate the role of photons by eliminating the photon degrees of freedom. Finally, I also dive into the strong spin-spin interaction regime, in which the Hamiltonian in weak disorders under the open boundary conditions resembles the two-block diagonal Gaussian orthogonal ensemble (GOE) of random matrices.
In Chapter 3, I successfully set up a prethermal state with lower entanglement entropy in the spin chain coupled with a cavity system. This is achieved for an exponentially long time through large-frequency periodic driving before the system heats up to an infinite-temperature state.
In Chapter 4, I summarize the two intriguing non-equilibrium phenomena observed in the spin chain in a cavity model and discuss the challenges encountered in my research.
In Chapter 1, I introduce the concept of thermalization in isolated quantum systems, along with the entanglement and spectral properties of thermalization. I also discuss the many-body localization (MBL) phase, which breaks down ETH by inducing a strong disorder, a phenomenon confirmed by theoretical and experimental work. Furthermore, I introduce Floquet prethermalization, which can be established without the need for disorder.
In Chapter 2, I explore the MBL of a quantum system coupled with photons. Although coupled with photons, the entanglement entropy and spectral form factor show the possible existence of finite-size MBL in the spin chain system. Additionally, I investigate the role of photons by eliminating the photon degrees of freedom. Finally, I also dive into the strong spin-spin interaction regime, in which the Hamiltonian in weak disorders under the open boundary conditions resembles the two-block diagonal Gaussian orthogonal ensemble (GOE) of random matrices.
In Chapter 3, I successfully set up a prethermal state with lower entanglement entropy in the spin chain coupled with a cavity system. This is achieved for an exponentially long time through large-frequency periodic driving before the system heats up to an infinite-temperature state.
In Chapter 4, I summarize the two intriguing non-equilibrium phenomena observed in the spin chain in a cavity model and discuss the challenges encountered in my research.
