The strange correlator [Phys. Rev. Lett. 112, 247202 (2014)] has been proposed as a measure of symmetry protected topological order in one- and two-dimensional systems. It takes the form of a spin-spin correlation function, computed as a mixed overlap between the state of interest and a trivial local product state. We demonstrate that it can be computed exactly (asymptotically, in the Monte Carlo sense) for various Affleck-Kennedy-Lieb-Tasaki states by direct evaluation of the wave function within the valence bond loop gas framework. We present results for lattices with chain, square, honeycomb, cube, diamond, and hyperhoneycomb geometries. In each case, the spin quantum number S is varied such that 2S (the number of valence bonds emerging from each site) achieves various integer multiples of the lattice coordination number. We introduce the concept of strange correlator loop winding number and point to its utility in testing for the presence of symmetry protected topological order.
Distinguishing the nontrivial symmetry-protected topological (SPT) phase from the trivial insulator phase in the presence of electron-electron interaction is an urgent question to the study of topological insulators, due to the fact that most of the topological indices defined for free electron systems are very likely unsuitable for interacting cases. In this work, we demonstrate that the strange correlator is a sensitive diagnosis to detect SPT states in interacting systems. Employing large-scale quantum Monte Carlo (QMC) simulations, we investigate the interaction-driven quantum phase transi…
We employ strange correlators to detect 2D subsystem symmetry-protected topological (SSPT) phases which are nontrivial topological phases protected by subsystem symmetries. Specifically, we analytically construct efficient strange correlators in the 2D cluster model in the presence of a uniform magnetic field and then perform the projector Quantum Monte Carlo simulation within the quantum annealing scheme. We find that strange correlators show the long-range correlation in the SSPT phase, from which we define strange order parameters to characterize the topological phase transition between the…
We extend the concept of strange correlators, defined for symmetry-protected phases in [You et al., Phys. Rev. Lett. 112, 247202 (2014)], to topological phases of matter by taking the inner product between string-net ground states and product states. The resulting two-dimensional partition functions are shown to be either critical or symmetry broken, as the corresponding transfer matrices inherit all matrix product operator symmetries of the string-net states. For the case of critical systems, those non-local matrix product operator symmetries are the lattice remnants of topological conformal …
Fidelity Strange Correlators for Average Symmetry-Protected Topological Phases
The Pennsylvania State University（宾夕法尼亚州立大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；Fudan University（复旦大学）；Collaborative Innovation Center of Advanced Microstructures（先进微结构协同创新中心）
We study the behavior of the recently proposed "strange correlator" [Phys. Rev. Lett. {\bf 112}, 247202 (2014)] in spin-1 Heisenberg antiferromagnetic chains with uniaxial single-ion anisotropy. Using projective quantum Monte Carlo, we are able to directly access the strange correlator in a variety of phases, as well as to examine its critical behavior at the quantum phase transition between trivial and non-trivial symmetry protected topological phases. After finding the expected long-range behavior in these two symmetry conserving phases, we go on to verify the topological nature of two-leg a…
We demonstrate the following conclusion: If $|Ψ\rangle$ is a $1d$ or $2d$ nontrivial short range entangled state, and $|Ω\rangle$ is a trivial disordered state defined on the same Hilbert space, then the following quantity (so called strange correlator) $C(r, r^\prime) = \frac{\langle Ω|ϕ(r) ϕ(r^\prime) | Ψ\rangle}{\langle Ω| Ψ\rangle}$ either saturates to a constant or decays as a power-law in the limit $|r - r^\prime| \rightarrow +\infty$, even though both $| Ω\rangle$ and $| Ψ\rangle$ are quantum disordered states with short-range correlation. $ϕ(r)$ is some local operator in the Hilbert sp…
The multi-scale entanglement renormalization ansatz (MERA) is a tensor network that can efficiently parameterize critical ground states on a 1D lattice, and also suggestively implement some aspects of the holographic correspondence of string theory on a lattice. Extending our recent work [S. Singh, Physical Review D 97, 026012 (2018); S. Singh, N. A. McMahon, and G. K. Brennen, Phys. Rev. D 97, 026013 (2018)], we show how the MERA representation of a 1D critical ground state---which has long range entanglement---can be viewed as a strange correlator: the overlap of a 2D state with short range …
Detecting underlying symmetry-protected topological phases via strange correlators and edge engineering
Beijing Normal University（北京师范大学）；Westlake University（西湖大学）；Westlake Institute for Advanced Study（西湖高等研究院）；The Hong Kong University of Science and Technology（香港科技大学）；Beihang University（北京航空航天大学）；Tianmushan Laboratory（天目山实验室）
The Sachdev-Ye-Kitaev (SYK) model describes a strange metal that shows peculiar non-Fermi liquid properties without quasiparticles. It exhibits a maximally chaotic behavior characterized by out-of-time-ordered correlators (OTOCs), and is expected to be a holographic dual to black holes. Recently, a striking similarity between the SYK model and the Hund-coupling induced spin-freezing crossover in multi-orbital Hubbard models has been pointed out. To further explore this connection, we study OTOCs for fermionic Hubbard models, which are prototypical models for strongly correlated electrons in so…
This paper describes a semiclassical field-theory approach to the topological properties of spatially featureless Affleck-Kennedy-Lieb-Tasaki type valence bond solid ground states of antiferromagnets in spatial dimensions one to three. Using nonlinear sigma models set in the appropriate target manifold and augmented with topological terms, we argue that the path integral representation of the ground-state wave functional can correctly distinguish symmetry-protected topological ground states from topologically trivial ones. The symmetry-protection feature is demonstrated explicitly in terms of …
Revealing the topology of quantum states via Kirkwood-Dirac quasiprobabilities
Istituto Nazionale di Ottica (INO), Consiglio Nazionale delle Ricerche（意大利国家光学研究所，意大利国家研究委员会）；European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze（欧洲非线性光谱学实验室，佛罗伦萨大学）；Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università di Parma（帕尔马大学数学、物理与信息科学系）；Gruppo Collegato di Parma, INFN-Sezione Milano-Bicocca（帕尔马联合小组，INFN米兰比可卡分部）；UdR Parma, INSTM（帕尔马研究组，意大利材料科学与技术研究中心）
