Entanglement and matrix product states in one-dimensional quantum lattice systems

Sangwoo S. Chung

The central topic of this thesis is on the fermionic continuous matrix product states (cMPS) variational ansatz for many-body quantum systems in a one-dimensional (1D) continuum.The matrix product states (MPS) is a variational ansatz which has been tremendously successful for nearly two decades in efficiently approximating groundstate properties of low-dimensional quantum lattice systems.The MPS is intrinsically designed for discrete lattice systems, however, and the cMPS has been introduced in 2010 as a continuum analogue of the MPS, enabling the possibility to directly tackle systems of quantum gases and liquids without resorting to discretization of space.

Paola Ruggiero

祝敬敏

Jing-Min Zhu

We present a new model of quantum phase transitions in matrix product systems of one-dimensional spin-1 chains and study the phases coexistence phenomenon. We find that in the thermodynamic limit the proposed system has three different quantum phases and by adjusting the control parameters we are able to realize any phase, any two phases equal coexistence and the three phases equal coexistence. At every critical point the physical quantities including the entanglement are not discontinuous and the matrix product system has long-range correlation and N -spin maximal entanglement. We believe that our work is helpful for having a comprehensive understanding of quantum phase transitions in matrix product states of one-dimensional spin chains and of certain directive significance to the preparation and control of one-dimensional spin lattice models with stable coherence and N -spin maximal entanglement.

S. M. Zangi, Chitra Shukla, Khalid Naseer +1 more

Xiangjian Qian, Mingpu Qin

Density matrix renormalization group (DMRG) or matrix product states (MPS) is the most effective and accurate method for studying one-dimensional quantum many-body systems. However, the application of DMRG to two-dimensional systems is not as successful because of the limited entanglement encoded in the wave-function ansatz. The fully augmented matrix product states (FAMPS), introduced recently in [Chin. Phys. Lett. 40, 057102 (2023)], extends MPS formalism to two dimensions and increases the entanglement in the wave-function ansatz, representing a significant advance in the simulation of two-dimensional quantum many-body physics. In the study of one-dimensional systems, the concept of a parent Hamiltonian for MPS has proven pivotal in the understanding of quantum entanglement. In this work, we extend this framework to two-dimensional systems. We illustrate the procedure to construct a two-dimensional Hamiltonian with given FAMPS as its exact ground state (the parent Hamiltonian for FAMPS). Additionally, through numerical simulations, we demonstrate the effectiveness of the algorithm outlined in [Chin. Phys. Lett. 40, 057102 (2023)] in precisely identifying the FAMPS for the constructed parent Hamiltonian. The introduction of FAMPS and its associated parent Hamiltonian provides a useful framework for the future investigations of two-dimensional quantum many-body systems.