@article { WOS:000707469900008,
title = {Superconductors with anomalous Floquet higher-order topology},
journal = {Phys. Rev. B},
volume = {104},
number = {14},
year = {2021},
month = {OCT 11},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We develop a general theory for two-dimensional (2D) anomalous Floquet higher-order topological superconductors (AFHOTSCs), which are dynamical Majorana-carrying phases of matter with no static counterpart. Despite the triviality of its bulk Floquet bands, an AFHOTSC generically features the simultaneous presence of corner-localized Majorana modes at both zero and pi/T quasienergies, a phenomenon beyond the scope of any static topological band theory. We show that the key to AFHOTSCs is their unavoidable singular behavior in the phase spectrum of the bulk time-evolution operator. By mapping such evolution-phase singularities to the stroboscopic boundary signatures, we classify 2D AFHOTSCs that are protected by a rotation group symmetry in symmetry class D. We further extract a higher-order topological index for unambiguously predicting the presence of Floquet corner Majorana modes, which we confirm numerically. Our theory serves as a milestone towards a dynamical topological theory for Floquet superconducting systems.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.L140502},
author = {Vu, DinhDuy and Zhang, Rui-Xing and Yang, Zhi-Cheng and Das Sarma, S.}
}
@article {zhang_tunable_2021,
title = {Tunable fragile topology in {Floquet} systems},
journal = {Phys. Rev. B},
volume = {103},
number = {12},
year = {2021},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {mar},
abstract = {We extend the notion of fragile topology to periodically driven systems. We demonstrate driving-induced fragile topology in two different models, namely, the Floquet honeycomb model and the Floquet pi-flux square-lattice model. In both cases, we discover a rich phase diagram that includes Floquet fragile topological phases protected by crystalline rotation or mirror symmetries, Floquet Chern insulators, and trivial atomic phases, with distinct boundary features. Remarkably, the transitions between different phases can be feasibly achieved by simply tuning the driving amplitudes, which is a unique feature of driving-enabled topological phenomena. Moreover, corner-localized fractional charges are identified as a {\textquotedblleft}smoking-gun{\textquotedblright} signal of fragile topology in our systems. Our work paves the way for studying and realizing fragile topology in Floquet systems.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.103.L121115},
author = {Zhang, Rui-Xing and Yang, Zhi-Cheng}
}
@article { WOS:000707473300010,
title = {Yang-Lee edge singularity triggered entanglement transition},
journal = {Phys. Rev. B},
volume = {104},
number = {16},
year = {2021},
month = {OCT 11},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We show that a class of PT symmetric non-Hermitian Hamiltonians realizing the Yang-Lee edge singularity exhibits an entanglement transition in the long-time steady state evolved under the Hamiltonian. Such a transition is induced by a level crossing triggered by the critical point associated with the Yang-Lee singularity and hence is first order in nature. At the transition, the entanglement entropy of the steady state jumps discontinuously from a volume-law to an area-law scaling. We exemplify this mechanism using a one-dimensional transverse field Ising model with additional imaginary fields, as well as the spin-1 Blume-Capel model and the three-state Potts model. We further make a connection to the forced-measurement induced entanglement transition in a Floquet nonunitary circuit subject to continuous measurements followed by post-selections. Our results demonstrate a new mechanism for entanglement transitions in non-Hermitian systems harboring a critical point.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.L161107},
author = {Jian, Shao-Kai and Yang, Zhi-Cheng and Bi, Zhen and Chen, Xiao}
}
@article { WOS:000688493300002,
title = {Z(2) topological order and first-order quantum phase transitions in systems with combinatorial gauge symmetry},
journal = {Phys. Rev. B},
volume = {104},
number = {8},
year = {2021},
month = {AUG 24},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We study a generalization of the two-dimensional transverse-field Ising model, combining both ferromagnetic and antiferromagnetic two-body interactions, that hosts exact global and local Z(2) gauge symmetries. Using exact diagonalization and stochastic series expansion quantum Monte Carlo methods, we confirm the existence of the topological phase in line with previous theoretical predictions. Our simulation results show that the transition between the confined topological phase and the deconfined paramagnetic phase is of first order, in contrast to the conventional Z(2) lattice gauge model in which the transition maps onto that of the standard Ising model and is continuous. We further generalize the model by replacing the transverse field on the gauge spins with a ferromagnetic XX interaction while keeping the local gauge symmetry intact. We find that the Z(2) topological phase remains stable, while the paramagnetic phase is replaced by a ferromagnetic phase. The topological-ferromagnetic quantum phase transition is also of first order. For both models, we discuss the low-energy spinon and vison excitations of the topological phase and their avoided level crossings associated with the first-order quantum phase transitions.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.085145},
author = {Wu, Kai-Hsin and Yang, Zhi-Cheng and Green, Dmitry and Sandvik, Anders W. and Chamon, Claudio}
}
@article { WOS:000685127300001,
title = {Z(3) Quantum Double in a Superconducting Wire Array},
journal = {PRX Quantum},
volume = {2},
number = {3},
year = {2021},
month = {AUG 13},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We show that a Z(3) quantum double can be realized in an array of superconducting wires coupled via Josephson junctions. With a suitably chosen magnetic flux threading the system, the interwire Josephson couplings take the form of a complex Hadamard matrix, which possesses combinatorial gauge symmetry-a local Z(3) symmetry involving permutations and shifts by +/- 2 pi/3 of the superconducting phases. The sign of the star potential resulting from the Josephson energy is inverted in this physical realization, leading to a massive degeneracy in the nonzero flux sectors. A dimerization pattern encoded in the capacitances of the array lifts up these degeneracies, resulting in a Z(3) topologically ordered state. Moreover, this dimerization pattern leads to a larger effective vison gap as compared to the canonical case with the usual (uninverted) star term. We further show that our model maps to a quantum three-state Potts model under a duality transformation. We argue, using a combination of bosonization and mean field theory, that altering the dimerization pattern of the capacitances leads to a transition from the Z(3) topological phase into a quantum XY-ordered phase. Our work highlights that combinatorial gauge symmetry can serve as a design principle to build quantum double models using systems with realistic interactions.},
doi = {10.1103/PRXQuantum.2.030327},
author = {Yang, Zhi-Cheng and Green, Dmitry and Yu, Hongji and Chamon, Claudio}
}
@article {liu_circuit_2020,
title = {Circuit complexity across a topological phase transition},
journal = {Phys. Rev. Res.},
volume = {2},
number = {1},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {mar},
abstract = {We use Nielsen{\textquoteright}s geometric approach to quantify the circuit complexity in a one-dimensional Kitaev chain across a topological phase transition. We find that the circuit complexities of both the ground states and nonequilibrium steady states of the Kitaev model exhibit nonanalytical behaviors at the critical points, and thus can be used to detect both equilibrium and dynamical topological phase transitions. Moreover, we show that the locality property of the real-space optimal Hamiltonian connecting two different ground states depends crucially on whether the two states belong to the same or different phases. This provides a concrete example of classifying different gapped phases using Nielsen{\textquoteright}s circuit complexity. We further generalize our results to a Kitaev chain with long-range pairing, and we discuss generalizations to higher dimensions. Our result opens up an avenue for using circuit complexity as a tool to understand quantum many-body systems.},
doi = {10.1103/PhysRevResearch.2.013323},
author = {Liu, Fangli and Whitsitt, Seth and Curtis, Jonathan B. and Lundgren, Rex and Titum, Paraj and Yang, Zhi-Cheng and Garrison, James R. and Gorshkov, V, Alexey}
}
@article {yang_extended_2020,
title = {Extended nonergodic regime and spin subdiffusion in disordered {SU}(2)-symmetric {Floquet} systems},
journal = {Phys. Rev. B},
volume = {102},
number = {21},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {dec},
abstract = {We explore thermalization and quantum dynamics in a one-dimensional disordered SU(2)-symmetric Floquet model, where a many-body localized phase is prohibited by the non-Abelian symmetry. Despite the absence of localization, we find an extended nonergodic regime at strong disorder where the system exhibits nonthermal behaviors. In the strong disorder regime, the level spacing statistics exhibit neither a Wigner-Dyson nor a Poisson distribution, and the spectral form factor does not show a linear-in-time growth at early times characteristic of random matrix theory. The average entanglement entropy of the Floquet eigenstates is subthermal, although violating an area-law scaling with system sizes. We further compute the expectation value of local observables and find strong deviations from the eigenstate thermalization hypothesis. The infinite-temperature spin autocorrelation function decays at long times as t(-beta) with beta {\textless} 0.5, indicating subdiffusive transport at strong disorders.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.102.214205},
author = {Yang, Zhi-Cheng and Nicholls, Stuart and Cheng, Meng}
}
@article { ISI:000535205600016,
title = {Hilbert-Space Fragmentation from Strict Confinement},
journal = {Phys. Rev. Lett.},
volume = {124},
number = {20},
year = {2020},
month = {MAY 22},
pages = {207602},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We study one-dimensional spin-1/2 models in which strict confinement of Ising domain walls leads to the fragmentation of Hilbert space into exponentially many disconnected subspaces. Whereas most previous works emphasize dipole moment conservation as an essential ingredient for such fragmentation, we instead require two commuting U(1) conserved quantities associated with the total domain-wall number and the total magnetization. The latter arises naturally from the confinement of domain walls. Remarkably, while some connected components of the Hilbert space thermalize, others are integrable by Bethe ansatz. We further demonstrate how this Hilbert-space fragmentation pattern arises perturbatively in the confining limit of Z(2) gauge theory coupled to fermionic matter, leading to a hierarchy of timescales for motion of the fermions. This model can be realized experimentally in two complementary settings.},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.124.207602},
author = {Yang, Zhi-Cheng and Liu, Fangli and Gorshkov, V, Alexey and Iadecola, Thomas}
}
@article {ISI:000465163400005,
title = {Hierarchical Majoranas in a programmable nanowire network},
journal = {Phys. Rev. B},
volume = {99},
number = {15},
year = {2019},
month = {APR 19},
pages = {155138},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We propose a hierarchical architecture for building {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero modes using {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majorana zero modes at the Y-junctions of a hexagonal network of semiconductor nanowires. Each Y-junction contains three {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majoranas, which hybridize when placed in close proximity, yielding a single effective Majorana mode near zero energy. The hybridization of effective Majorana modes on neighboring Y-junctions is controlled by applied gate voltages on the links of the honeycomb network. This gives rise to a tunable tight-binding model of effective Majorana modes. We show that selecting the gate voltages that generate a Kekule vortex pattern in the set of hybridization amplitudes yields an emergent {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero mode bound to the vortex core. The position of a logical Majorana can be tuned adiabatically, without moving any of the {\textquoteleft}{\textquoteleft}physical{{\textquoteright}{\textquoteright}} Majoranas or closing any energy gaps, by programming the values of the gate voltages to change as functions of time. A nanowire network supporting multiple such {\textquoteleft}{\textquoteleft}logical{{\textquoteright}{\textquoteright}} Majorana zero modes provides a physical platform for performing adiabatic non-Abelian braiding operations in a fully controllable manner.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.99.155138},
author = {Yang, Zhi-Cheng and Iadecola, Thomas and Chamon, Claudio and Mudry, Christopher}
}