scholarly journals Relating the topology of Dirac Hamiltonians to quantum geometry: When the quantum metric dictates Chern numbers and winding numbers

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Bruno Mera ◽  
Anwei Zhang ◽  
Nathan Goldman
Keyword(s):  
Quantum Physics ◽  
Berry Phase ◽  
Broad Class ◽  
Topological States Of Matter ◽  
Quantum Geometry ◽  
Special Cases ◽  
Chern Numbers ◽  
Spatial Dimensions ◽  
Topological States ◽  
Engineered Systems

Quantum geometry has emerged as a central and ubiquitous concept in quantum sciences, with direct consequences on quantum metrology and many-body quantum physics. In this context, two fundamental geometric quantities are known to play complementary roles:~the Fubini-Study metric, which introduces a notion of distance between quantum states defined over a parameter space, and the Berry curvature associated with Berry-phase effects and topological band structures. In fact, recent studies have revealed direct relations between these two important quantities, suggesting that topological properties can, in special cases, be deduced from the quantum metric. In this work, we establish general and exact relations between the quantum metric and the topological invariants of generic Dirac Hamiltonians. In particular, we demonstrate that topological indices (Chern numbers or winding numbers) are bounded by the quantum volume determined by the quantum metric. Our theoretical framework, which builds on the Clifford algebra of Dirac matrices, is applicable to topological insulators and semimetals of arbitrary spatial dimensions, with or without chiral symmetry. This work clarifies the role of the Fubini-Study metric in topological states of matter, suggesting unexplored topological responses and metrological applications in a broad class of quantum-engineered systems.

scholarly journals Is there contextuality in behavioural and social systems?

2016 ◽  
Vol 374 (2058) ◽  
pp. 20150099 ◽  
Author(s):  
E. N. Dzhafarov ◽  
Ru Zhang ◽  
Janne Kujala
Keyword(s):  
Quantum Physics ◽  
Broad Class ◽  
Social Systems ◽  
Sufficient Conditions ◽  
Type Systems ◽  
Binary Outcomes ◽  
Special Cases ◽  
Einstein Podolsky Rosen ◽  
Cyclic Systems ◽  
Necessary And Sufficient

Most behavioural and social experiments aimed at revealing contextuality are confined to cyclic systems with binary outcomes. In quantum physics, this broad class of systems includes as special cases Klyachko–Can–Binicioglu–Shumovsky-type, Einstein–Podolsky–Rosen–Bell-type and Suppes–Zanotti–Leggett–Garg-type systems. The theory of contextuality known as contextuality-by-default allows one to define and measure contextuality in all such systems, even if there are context-dependent errors in measurements, or if something in the contexts directly interacts with the measurements. This makes the theory especially suitable for behavioural and social systems, where direct interactions of ‘everything with everything’ are ubiquitous. For cyclic systems with binary outcomes, the theory provides necessary and sufficient conditions for non-contextuality, and these conditions are known to be breached in certain quantum systems. We review several behavioural and social datasets (from polls of public opinion to visual illusions to conjoint choices to word combinations to psychophysical matching), and none of these data provides any evidence for contextuality. Our working hypothesis is that this may be a broadly applicable rule: behavioural and social systems are non-contextual, i.e. all ‘contextual effects’ in them result from the ubiquitous dependence of response distributions on the elements of contexts other than the ones to which the response is presumably or normatively directed.

scholarly journals Tensor Monopoles in superconducting systems

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 601
Author(s):  
H. Weisbrich ◽  
M. Bestler ◽  
W. Belzig
Keyword(s):  
Topological Structure ◽  
Gauge Theories ◽  
Topological States Of Matter ◽  
Three Dimensions ◽  
Gauge Fields ◽  
Quantum Geometry ◽  
Central Concept ◽  
Dirac Monopole ◽  
Topological States ◽  
Phase Differences

Topology in general but also topological objects such as monopoles are a central concept in physics. They are prime examples for the intriguing physics of gauge theories and topological states of matter. Vector monopoles are already frequently discussed such as the well-established Dirac monopole in three dimensions. Less known are tensor monopoles giving rise to tensor gauge fields. Here we report that tensor monopoles can potentially be realized in superconducting multi-terminal systems using the phase differences between superconductors as synthetic dimensions. In a first proposal we suggest a circuit of superconducting islands featuring charge states to realize a tensor monopole. As a second example we propose a triple dot system coupled to multiple superconductors that also gives rise to such a topological structure. All proposals can be implemented with current experimental means and the monopole readily be detected by measuring the quantum geometry.

scholarly journals Experimental measurement of the quantum geometric tensor using coupled qubits in diamond

2019 ◽  
Vol 7 (2) ◽  
pp. 254-260 ◽  
Author(s):  
Min Yu ◽  
Pengcheng Yang ◽  
Musang Gong ◽  
Qingyun Cao ◽  
Qiuyu Lu ◽  
...  
Keyword(s):  
Experimental Measurement ◽  
Topological States Of Matter ◽  
Topological Defects ◽  
Quantum Geometry ◽  
And Topology ◽  
Wide Range ◽  
Nv Center ◽  
Topological States ◽  
Physical Phenomena ◽  
Complete Quantum

Abstract Geometry and topology are fundamental concepts, which underlie a wide range of fascinating physical phenomena such as topological states of matter and topological defects. In quantum mechanics, the geometry of quantum states is fully captured by the quantum geometric tensor. Using a qubit formed by an NV center in diamond, we perform the first experimental measurement of the complete quantum geometric tensor. Our approach builds on a strong connection between coherent Rabi oscillations upon parametric modulations and the quantum geometry of the underlying states. We then apply our method to a system of two interacting qubits, by exploiting the coupling between the NV center spin and a neighboring 13C nuclear spin. Our results establish coherent dynamical responses as a versatile probe for quantum geometry, and they pave the way for the detection of novel topological phenomena in solid state.

scholarly journals Quantum entangled fractional topology and curvatures

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Joel Hutchinson ◽  
Karyn Le Hur
Keyword(s):  
Dirac Point ◽  
Berry Phase ◽  
Honeycomb Lattice ◽  
Topological Spaces ◽  
Global Response ◽  
Quantum Matter ◽  
Chern Numbers ◽  
Topological States ◽  
Spin Response ◽  
The Stability

AbstractTopological spaces have numerous applications for quantum matter with protected chiral edge modes related to an integer-valued Chern number, which also characterizes the global response of a spin-1/2 particle to a magnetic field. Such spin-1/2 models can also describe topological Bloch bands in lattice Hamiltonians. Here we introduce interactions in a system of spin-1/2s to reveal a class of topological states with rational-valued Chern numbers for each spin providing a geometrical and physical interpretation related to curvatures and quantum entanglement. We study a driving protocol in time to reveal the stability of the fractional topological numbers towards various forms of interactions in the adiabatic limit. We elucidate a correspondence of a one-half topological spin response in bilayer semimetals on a honeycomb lattice with a nodal ring at one Dirac point and a robust π Berry phase at the other Dirac point.

scholarly journals Towards the manipulation of topological states of matter: a perspective from electron transport

2018 ◽  
Vol 63 (9) ◽  
pp. 580-594 ◽  
Author(s):  
Cheng Zhang ◽  
Hai-Zhou Lu ◽  
Shun-Qing Shen ◽  
Yong P. Chen ◽  
Faxian Xiu
Keyword(s):  
Electron Transport ◽  
Topological States Of Matter ◽  
Topological States

scholarly journals Measuring Chern numbers in Hofstadter strips

2017 ◽  
Vol 3 (2) ◽  
Author(s):  
Samuel Mugel ◽  
Alexandre Dauphin ◽  
Pietro Massignan ◽  
Leticia Tarruell ◽  
Maciej Lewenstein ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Periodic Boundary Conditions ◽  
Chern Number ◽  
Open Boundary ◽  
Topological Invariants ◽  
Transverse Displacement ◽  
Open Boundary Conditions ◽  
Open Questions ◽  
Chern Numbers ◽  
Spatial Dimensions

Topologically non-trivial Hamiltonians with periodic boundary conditions are characterized by strictly quantized invariants. Open questions and fundamental challenges concern their existence, and the possibility of measuring them in systems with open boundary conditions and limited spatial extension. Here, we consider transport in Hofstadter strips, that is, two-dimensional lattices pierced by a uniform magnetic flux which extend over few sites in one of the spatial dimensions. As we show, an atomic wave packet exhibits a transverse displacement under the action of a weak constant force. After one Bloch oscillation, this displacement approaches the quantized Chern number of the periodic system in the limit of vanishing tunneling along the transverse direction. We further demonstrate that this scheme is able to map out the Chern number of ground and excited bands, and we investigate the robustness of the method in presence of both disorder and harmonic trapping. Our results prove that topological invariants can be measured in Hofstadter strips with open boundary conditions and as few as three sites along one direction.

scholarly journals Structure and Uncertainty in Discrete Choice Models

2003 ◽  
Vol 11 (4) ◽  
pp. 316-344 ◽  
Author(s):  
Curtis S. Signorino
Keyword(s):  
Discrete Choice ◽  
Private Information ◽  
Statistical Models ◽  
Broad Class ◽  
Choice Models ◽  
Discrete Choice Models ◽  
Social Scientists ◽  
Sources Of Uncertainty ◽  
Special Cases

Social scientists are often confronted with theories in which one or more actors make choices over a discrete set of options. In this article, I generalize a broad class of statistical discrete choice models, with both well-known and new nonstrategic and strategic special cases. I demonstrate how to derive statistical models from theoretical discrete choice models and, in doing so, I address the statistical implications of three sources of uncertainty: agent error, private information about payoffs, and regressor error. For strategic and some nonstrategic choice models, the three types of uncertainty produce different statistical models. In these cases, misspecifying the type of uncertainty leads to biased and inconsistent estimates, and to incorrect inferences based on estimated probabilities.

scholarly journals Oxygen vacancy-driven orbital multichannel Kondo effect in Dirac nodal line metals IrO2 and RuO2

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Sheng-Shiuan Yeh ◽  
Ta-Kang Su ◽  
An-Shao Lien ◽  
Farzaneh Zamani ◽  
Johann Kroha ◽  
...  
Keyword(s):  
Kondo Effect ◽  
High Temperature Superconductivity ◽  
Topological States Of Matter ◽  
Nodal Line ◽  
Metallic State ◽  
Strong Electron ◽  
Quantum Matter ◽  
Kondo Physics ◽  
Topological States ◽  
Weak Coupling Theory

Abstract Strong electron correlations have long been recognized as driving the emergence of novel phases of matter. A well recognized example is high-temperature superconductivity which cannot be understood in terms of the standard weak-coupling theory. The exotic properties that accompany the formation of the two-channel Kondo (2CK) effect, including the emergence of an unconventional metallic state in the low-energy limit, also originate from strong electron interactions. Despite its paradigmatic role for the formation of non-standard metal behavior, the stringent conditions required for its emergence have made the observation of the nonmagnetic, orbital 2CK effect in real quantum materials difficult, if not impossible. We report the observation of orbital one- and two-channel Kondo physics in the symmetry-enforced Dirac nodal line (DNL) metals IrO2 and RuO2 nanowires and show that the symmetries that enforce the existence of DNLs also promote the formation of nonmagnetic Kondo correlations. Rutile oxide nanostructures thus form a versatile quantum matter platform to engineer and explore intrinsic, interacting topological states of matter.

scholarly journals Topological transitions in an oscillatory driven liquid crystal cell

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Marcel G. Clerc ◽  
Michał Kowalczyk ◽  
Valeska Zambra
Keyword(s):  
Liquid Crystal ◽  
Topological States Of Matter ◽  
Low Frequency ◽  
Vortex State ◽  
Liquid Crystal Cell ◽  
Topological Transition ◽  
Exotic States ◽  
Crystal Cell ◽  
Topological States ◽  
Topological Transitions

Abstract Matter under different equilibrium conditions of pressure and temperature exhibits different states such as solid, liquid, gas, and plasma. Exotic states of matter, such as Bose–Einstein condensates, superfluidity, chiral magnets, superconductivity, and liquid crystalline blue phases are observed in thermodynamic equilibrium. Rather than being a result of an aggregation of matter, their emergence is due to a change of a topological state of the system. These topological states can persist out of thermodynamics equilibrium. Here we investigate topological states of matter in a system with injection and dissipation of energy by means of oscillatory forcing. In an experiment involving a liquid crystal cell under the influence of a low-frequency oscillatory electric field, we observe a transition from a non-vortex state to a state in which vortices persist, topological transition. Depending on the period and the type of the forcing, the vortices self-organise, forming square lattices, glassy states, and disordered vortex structures. The bifurcation diagram is characterised experimentally. A continuous topological transition is observed for the sawtooth and square forcings. The scenario changes dramatically for sinusoidal forcing where the topological transition is discontinuous, which is accompanied by serial transitions between square and glassy vortex lattices. Based on a stochastic amplitude equation, we recognise the origin of the transition as the balance between stochastic creation and deterministic annihilation of vortices. Numerical simulations show topological transitions and the emergence of square vortex lattice. Our results show that the matter maintained out of equilibrium by means of the temporal modulation of parameters can exhibit exotic states.

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