The matrix product state (MPS) is utilized to study the ground-state properties and quantum phase transitions (QPTs) of the one-dimensional extended quantum compass model (EQCM). The MPS wave functions are argued to be very efficient descriptions of the ground states, and are numerically determined by imaginary-time projections. The ground-state energy, correlations, quantum entanglement and its spectrum, local and nonlocal order parameters, etc., are calculated and studied in detail. It is revealed that the von Neumann entanglement entropy, as well as the nearest-neighbor correlation functions, can be used to detect the second-order QPTs, but not the first-order ones, while fidelity detections can recognize both. The entanglement spectrum is extracted from the MPS wave function and found to be doubly degenerate in disordered phases, where nonzero string order parameters exist. Moreover, with the linearized tensor renormalization group method, the specific-heat curves are evaluated and their low-temperature behaviors are investigated. Compared with the exact solutions, our results verify that these MPS-based numerical methods are very accurate and powerful, and can be employed to investigate other EQCMs which do not permit exact solutions at present.

• Received 13 January 2012

DOI:https://doi.org/10.1103/PhysRevB.85.184422