@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 {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}
}