Research Projects
A publication list can be found on My Google Scholar Page.
Research Projects
A publication list can be found on My Google Scholar Page.
Entanglement in (conformal) field theory
How to access the entanglement properties of many-body systems and extract universal information from them is an important and challenging question.
Qicheng Tang, Zixia Wei, Yin Tang, Xueda Wen and W. Zhu, Universal entanglement signatures of interface conformal field theories, Phys. Rev. B 109, L041104 (2024), arXiv: 2308.03646 [cond-mat.stat-mech].
We explore possible universal signatures about an interface gluing two distinct CFTs, by combing holographic calculation and lattice simulation. The results are potentially useful for characterizing the underlying universality of generic critical interface theories.
Yin Tang, Qicheng Tang, and W. Zhu, Thermal correction to entanglement spectrum for conformal field theories, JHEP08(2022)239, arXiv: 2206.10285 [hep-th].
We analytically derive the thermal correction to the entanglement spectrum for general two-dimensional conformal field theories.
Qicheng Tang and W. Zhu, Entanglement entropy in (2+1)D quantum critical points with quenched disorder: A dimensional reduction approach, Phys. Rev. B 106, 195152 (2022), arXiv: 2201.05035 [cond-mat.str-el].
We develop an analytic method to calculate the entanglement entropy for (2+1)-dimensional theories with quench disorders.
Qi-Cheng Tang and Wei Zhu, Critical Scaling Behaviors of Entanglement Spectra, Chin. Phys. Lett., 2020, 37 (1): 010301, arXiv: 1911.03125 [cond-mat.stat-mech].
We analytically solve the entanglement spectrum during global quench that is driven by a critical Hamiltonian. It is found that the conformal tower structure of the critical Hamiltonian can be encoded into the entanglement spectrum of a pure state via global quench.
Emergent criticality in non-unitary dynamics
Exploring novel critical systems from non-unitary dynamics is potentially helpful to build up the underlying paradigm in statistical physics.
Qicheng Tang and Xueda Wen, A critical state under weak measurement is not critical, arXiv: 2411.13705 [cond-mat.stat-mech] .
Critical states under certain measurement protocols exhibit typical signatures of criticality. However, by considering free Dirac fermions as a concrete example, we show that the post-measurement states are generally not critical, hosting a gapped and long-ranged entanglement Hamiltonian even in the single-interval case. This is distinct from the critical ground state, where the entanglement Hamiltonian for a single interval is gapless and local.
Qicheng Tang, Xiao Chen and W. Zhu, Quantum criticality in the nonunitary dynamics of (2+1)-dimensional free fermions, Phys. Rev. B 103, 174303 (2021) [editor’s suggestion], arXiv: 2101.04320 [cond-mat.stat-mech] .
We design a dynamical steady state with critical signatures of entanglement via nonunitary dynamics of free fermions. The emergent criticality, observed by large-scale numerical simulations, can be phenomenologically described by a master equation of two-point correlation and a quasi-particle picture of producing entanglement. Analytic results indicate the possible extension into general spatial dimensions.
Unconventional entanglement structure in non-unitary/non-hermitian systems
Non-unitary and non-hermitian systems host exotic phases of matter with unconventional entanglement structure.
Qicheng Tang and W. Zhu, Measurement-induced phase transition: A case study in the non-integrable model by density-matrix renormalization group calculations, Phys. Rev. Research 2, 013022 (2020), arXiv: 1908.11253 [cond-mat.stat-mech].
We provide one more example of the measurement-induced phase transition by density-matrix renormalization group calculations.
Symmetry breaking out of equilibrium
Non-equilibrium process provides a dynamical way to probe symmetry breaking.
Ruhanshi Barad, Qicheng Tang, Wei Zhu and Xueda Wen, Universal time evolution of string order parameter in quantum critical systems with boundary invertible or non-invertible symmetry breaking, arXiv: 2410.16402 [cond-mat.str-el].
By using conformal field theory techniques, we find that the string order parameter exhibits universal dynamical scaling behavior in critical systems with boundary/interface symmetry breaking.
Phase transition from electron structure
Traditional condensed matter physics (or said solid state physics) provides a way to access the properties of solid states from their band structure.
Qicheng Tang, L. A. Svyatkin, and I. P. Chernov, Influence of hydrogen on electron-phonon coupling and intrinsic electrical resistivity in zirconium: A first-principles study, Phys. Rev. B 99, 205152 (2019), arXiv: 1806.00847 [cond-mat.mtrl-sci].
We calculate the electron and phonon structure of zirconium with hydrogen atoms. By estimating the dependence of electron-phonon coupling with the concentration of hydrogen, we provide a link to the change of electrical resistivity and structural transition in zirconinum.