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Lezama, T. L. M., Bera, S. & Bardarson, J. H. (2019). Apparent slow dynamics in the ergodic phase of a driven many-body localized system without extensive conserved quantities. Physical Review B, 99(16), Article ID 161106.
Open this publication in new window or tab >>Apparent slow dynamics in the ergodic phase of a driven many-body localized system without extensive conserved quantities
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 16, article id 161106Article in journal (Refereed) Published
Abstract [en]

We numerically study the dynamics on the ergodic side of the many-body localization transition in a periodically driven Floquet model with no global conservation laws. We describe and employ a numerical technique based on the fast Walsh-Hadamard transform that allows us to perform an exact time evolution for large systems and long times. As in models with conserved quantities (e.g., energy and/or particle number) we observe a slowing down of the dynamics as the transition into the many-body localized phase is approached. More specifically, our data are consistent with a subballistic spread of entanglement and a stretched-exponential decay of an autocorrelation function, with their associated exponents reflecting slow dynamics near the transition for a fixed system size. However, with access to larger system sizes, we observe a clear flow of the exponents towards faster dynamics and cannot rule out that the slow dynamics is a finite-size effect. Furthermore, we observe examples of nonmonotonic dependence of the exponents with time, with the dynamics initially slowing down but accelerating again at even larger times, consistent with the slow dynamics being a crossover phenomenon with a localized critical point.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
Keywords
UTSCH JM, 1991, PHYSICAL REVIEW A, V43, P2046 gol Marcos, 2008, NATURE, V452, P854 rnyi IV, 2005, PHYSICAL REVIEW LETTERS, V95, osen Tomaz, 2007, JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICALSchool and Workshop on Theory and Technology in Quantum Information, Communication, Computation and Cryptography, JUN 12-23, 2006, Trieste, ITALY, V40, P7881 isse A, 2006, REVIEWS OF MODERN PHYSICS, V78, P275 tos X, 1997, PHYSICAL REVIEW B, V55, P11029
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-249784 (URN)10.1103/PhysRevB.99.161106 (DOI)000463888700002 ()2-s2.0-85064130532 (Scopus ID)
Note

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-04-29Bibliographically approved
Herviou, L., Bardarson, J. H. & Regnault, N. (2019). Defining a bulk-edge correspondence for non-Hermitian Hamiltonians via singular-value decomposition. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 99(5), Article ID 052118.
Open this publication in new window or tab >>Defining a bulk-edge correspondence for non-Hermitian Hamiltonians via singular-value decomposition
2019 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 99, no 5, article id 052118Article in journal (Refereed) Published
Abstract [en]

We address the breakdown of the bulk-boundary correspondence observed in non-Hermitian systems, where open and periodic systems can have distinct phase diagrams. The correspondence can be completely restored by considering the Hamiltonian's singular-value decomposition instead of its eigendecomposition. This leads to a natural topological description in terms of a flattened singular decomposition. This description is equivalent to the usual approach for Hermitian systems and coincides with a recent proposal for the classification of non-Hermitian systems. We generalize the notion of the entanglement spectrum to non-Hermitian systems, and show that the edge physics is indeed completely captured by the periodic bulk Hamiltonian. We exemplify our approach by considering the chiral non-Hermitian Su-Schrieffer-Heger and Chern insulator models. Our work advocates a different perspective on topological non-Hermitian Hamiltonians, paving the way to a better understanding of their entanglement structure.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Algebra and Logic
Identifiers
urn:nbn:se:kth:diva-254021 (URN)10.1103/PhysRevA.99.052118 (DOI)000469016300002 ()2-s2.0-85066879533 (Scopus ID)
Note

QC 20190620

Available from: 2019-06-20 Created: 2019-06-20 Last updated: 2019-06-20Bibliographically approved
Herviou, L., Bera, S. & Bardarson, J. H. (2019). Multiscale entanglement clusters at the many-body localization phase transition. Physical Review B, 99(13), Article ID 134205.
Open this publication in new window or tab >>Multiscale entanglement clusters at the many-body localization phase transition
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 13, article id 134205Article in journal (Refereed) Published
Abstract [en]

We numerically study the formation of entanglement clusters across the many-body localization transition. We observe a crossover from strong many-body entanglement in the ergodic phase to weak local correlations in the localized phase, with continuous clusters throughout the phase diagram. Critical states close to the transition have a structure compatible with fractal or multiscale-entangled states, characterized by entanglement at multiple levels: small strongly entangled clusters are weakly entangled together to form larger clusters. The critical point therefore features subthermal entanglement and a power-law distributed cluster size. Upon entering the localized phase, the power-law distribution seems to persist with a varying power that crosses over into a stretched exponent before eventually becoming exponential deep in the localized phase. These results are in agreement with some of the recently proposed phenomenological renormalization-group schemes characterizing the many-body localized critical point, and serve to constrain other such schemes.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-251481 (URN)10.1103/PhysRevB.99.134205 (DOI)000465150000002 ()2-s2.0-85065121087 (Scopus ID)
Note

QC 20190522

Available from: 2019-05-22 Created: 2019-05-22 Last updated: 2019-05-22Bibliographically approved
Kaladzhyan, V. & Bardarson, J. H. (2019). Quantized Fermi arc mediated transport in Weyl semimetal nanowires. Physical Review B, 100(8), Article ID 085424.
Open this publication in new window or tab >>Quantized Fermi arc mediated transport in Weyl semimetal nanowires
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085424Article in journal (Refereed) Published
Abstract [en]

We study longitudinal transport in Weyl semimetal nanowires, both in the absence and in the presence of a magnetic flux threading the nanowires. We identify two qualitatively different regimes of transport with respect to the chemical potential in the nanowires. In the "surface regime," for low doping, most of the conductance occurs through the Fermi arc surface states, and it rises in steps of one quantum of conductance as a function of the chemical potential; furthermore, with varying flux the conductance changes in steps of one quantum of conductance with characteristic Fabry-Perot interference oscillations. In the "bulk-surface regime," for highly doped samples, the dominant contribution to the conductance is quadratic in the chemical potential, and mostly conditioned by the bulk states; the flux dependence shows clearly that both the surface and the bulk states contribute. The two aforementioned regimes prove that the contribution of Fermi arc surface states is salient and, therefore, crucial for understanding transport properties of finite-size Weyl semimetal systems. Last but not least, we demonstrate that both regimes are robust to disorder.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-257435 (URN)10.1103/PhysRevB.100.085424 (DOI)000480687800004 ()2-s2.0-85072101886 (Scopus ID)
Note

QC 20190902

Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-10-04Bibliographically approved
Hauschild, J., Leviatan, E., Bardarson, J. H., Altman, E., Zaletel, M. P. & Pollmann, F. (2018). Finding purifications with minimal entanglement. Physical Review B, 98(23), Article ID 235163.
Open this publication in new window or tab >>Finding purifications with minimal entanglement
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 23, article id 235163Article in journal (Refereed) Published
Abstract [en]

Purification is a tool that allows to represent mixed quantum states as pure states on enlarged Hilbert spaces. A purification of a given state is not unique and its entanglement strongly depends on the particular choice made. Moreover, in one-dimensional systems, the amount of entanglement is linked to how efficiently the purified state can be represented using matrix-product states (MPS). We introduce an MPS based method that allows to find the minimally entangled representation by iteratively minimizing the second Renyi entropy. First, we consider the thermofield double purification and show that its entanglement can be strongly reduced especially at low temperatures. Second, we show that a slowdown of the entanglement growth following a quench of an infinite temperature state is possible.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-241194 (URN)10.1103/PhysRevB.98.235163 (DOI)000454630300001 ()2-s2.0-85059514028 (Scopus ID)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-01-21Bibliographically approved
Javanmard, Y., Trapin, D., Bera, S., Bardarson, J. H. & Heyl, M. (2018). Sharp entanglement thresholds in the logarithmic negativity of disjoint blocks in the transverse-field Ising chain. New Journal of Physics, 20, Article ID 083032.
Open this publication in new window or tab >>Sharp entanglement thresholds in the logarithmic negativity of disjoint blocks in the transverse-field Ising chain
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2018 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 083032Article in journal (Refereed) Published
Abstract [en]

Entanglement has developed into an essential concept for the characterization of phases and phase transitions in ground states of quantum many-body systems. In this work we use the logarithmic negativity to study the spatial entanglement structure in the transverse-field Ising chain both in the ground state and at nonzero temperatures. Specifically, we investigate the entanglement between two disjoint blocks as a function of their separation, which can be viewed as the entanglement analog of a spatial correlation function. We find sharp entanglement thresholds at a critical distance beyond which the logarithmic negativity vanishes exactly and thus the two blocks become unentangled, which holds even in the presence of long-ranged quantum correlations, i.e., at the system's quantum critical point. Using time-evolving block decimation, we explore this feature as a function of temperature and size of the two blocks and present a simple model to describe our numerical observations.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
ground states and nonzero temperature states of transverse-field Ising model, entanglement, logarithmic negativity, density matrices and partial transpose, entanglement threshold and sudden death of entanglement
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-234598 (URN)10.1088/1367-2630/aad9ba (DOI)000442724300002 ()2-s2.0-85053134016 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20180914

Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-10-16Bibliographically approved
Atteia, J., Bardarson, J. H. & Cayssol, J. (2017). Ballistic transport through irradiated graphene. Physical Review B, 96(24), Article ID 245404.
Open this publication in new window or tab >>Ballistic transport through irradiated graphene
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245404Article in journal (Refereed) Published
Abstract [en]

The coherent charge transport through an illuminated graphene ribbon is studied as a function of electronic doping and characteristics of the electromagnetic driving, for monochromatic circularly polarized light. We focus on the DC current carried by 2D bulk carriers which is dominant (over edge transport) for short and wide enough samples. We investigate how the ballistic conductance suppression, due to photon resonances between the valence and conduction bands, evolves when the experimentally tunable parameters are varied. The residual conductance can be associated with evanescent states and related to dynamical gaps in the Floquet quasienergy spectrum.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-227113 (URN)10.1103/PhysRevB.96.245404 (DOI)000417476100004 ()2-s2.0-85039412874 (Scopus ID)
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2019-10-18Bibliographically approved
Behrends, J., Rhim, J.-W., Liu, S., Grushin, A. G. & Bardarson, J. H. (2017). Nodal-line semimetals from Weyl superlattices. Physical Review B, 96(24), Article ID 245101.
Open this publication in new window or tab >>Nodal-line semimetals from Weyl superlattices
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245101Article in journal (Refereed) Published
Abstract [en]

The existence and topological classification of lower-dimensional Fermi surfaces is often tied to the crystal symmetries of the underlying lattice systems. Artificially engineered lattices, such as heterostructures and other superlattices, provide promising avenues to realize desired crystal symmetries that protect lower-dimensional Fermi surfaces, such as nodal lines. In this work, we investigate a Weyl semimetal subjected to spatially periodic onsite potential, giving rise to several phases, including a nodal-line semimetal phase. In contrast to proposals that purely focus on lattice symmetries, the emergence of the nodal line in this setup does not require small spin-orbit coupling, but rather relies on its presence. We show that the stability of the nodal line is understood from reflection symmetry and a combination of a fractional lattice translation and charge-conjugation symmetry. Depending on the choice of parameters, this model exhibits drumhead surface states that are exponentially localized at the surface, or weakly localized surface states that decay into the bulk at all energies.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-220263 (URN)10.1103/PhysRevB.96.245101 (DOI)000416848200003 ()2-s2.0-85039455476 (Scopus ID)
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3328-8525

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