109 research outputs found
Tensor Berry connections and their topological invariants
The Berry connection plays a central role in our description of the geometric
phase and topological phenomena. In condensed matter, it describes the parallel
transport of Bloch states and acts as an effective "electromagnetic" vector
potential defined in momentum space. Inspired by developments in mathematical
physics, where higher-form (Kalb-Ramond) gauge fields were introduced, we
hereby explore the existence of "tensor Berry connections" in quantum matter.
Our approach consists in a general construction of effective gauge fields,
which we ultimately relate to the components of Bloch states. We apply this
formalism to various models of topological matter, and we investigate the
topological invariants that result from generalized Berry connections. For
instance, we introduce the 2D Zak phase of a tensor Berry connection, which we
then relate to the more conventional first Chern number; we also reinterpret
the winding number characterizing 3D topological insulators to a Dixmier-Douady
invariant, which is associated with the curvature of a tensor connection.
Besides, our approach identifies the Berry connection of tensor monopoles,
which are found in 4D Weyl-type systems [Palumbo and Goldman, Phys. Rev. Lett.
121, 170401 (2018)]. Our work sheds light on the emergence of gauge fields in
condensed-matter physics, with direct consequences on the search for novel
topological states in solid-state and quantum-engineered systems.Comment: 10 pages, 1 table. Published versio
Revealing tensor monopoles through quantum-metric measurements
Monopoles are intriguing topological objects, which play a central role in
gauge theories and topological states of matter. While conventional monopoles
are found in odd-dimensional flat spaces, such as the Dirac monopole in three
dimensions and the non-Abelian Yang monopole in five dimensions, more exotic
objects were predicted to exist in even dimensions. This is the case of "tensor
monopoles", which are associated with generalized (tensor) gauge fields, and
which can be defined in four dimensional flat spaces. In this work, we
investigate the possibility of creating and measuring such a tensor monopole,
by introducing a realistic three-band model defined over a four-dimensional
parameter space. Our probing method is based on the observation that the
topological charge of this tensor monopole, which we relate to a generalized
Berry curvature, can be directly extracted from the quantum metric. We propose
a realistic three-level atomic system, where tensor monopoles could be
generated and revealed through quantum-metric measurements.Comment: 4+4 pages, 2 figures, Revised version containing new appendice
Non-Abelian Bloch oscillations in higher-order topological insulators
Bloch oscillations (BOs) are a fundamental phenomenon by which a wave packet
undergoes a periodic motion in a lattice when subjected to an external force.
Observed in a wide range of synthetic lattice systems, BOs are intrinsically
related to the geometric and topological properties of the underlying band
structure. This has established BOs as a prominent tool for the detection of
Berry phase effects, including those described by non-Abelian gauge fields. In
this work, we unveil a unique topological effect that manifests in the BOs of
higher-order topological insulators through the interplay of non-Abelian Berry
curvature and quantized Wilson loops. It is characterized by an oscillating
Hall drift that is synchronized with a topologically-protected inter-band
beating and a multiplied Bloch period. We elucidate that the origin of this
synchronization mechanism relies on the periodic quantum dynamics of Wannier
centers. Our work paves the way to the experimental detection of non-Abelian
topological properties in synthetic matter through the measurement of Berry
phases and center-of-mass displacements.Comment: 13 pages, 6 figure
Hybrid metal oxide cycle water splitting
Hybrid thermochemical water splitting cycles are provided in which thermally reduced metal oxides particles are used to displace some but not all of the electrical requirements in a water splitting electrolytic cell. In these hybrid cycles, the thermal reduction temperature is significantly reduced compared to two-step metal-oxide thermochemical cycles in which only thermal energy is required to produce hydrogen from water. Also, unlike the conventional higher temperature cycles where the reduction step must be carried out under reduced oxygen pressure, the reduction step in the proposed hybrid cycles can be carried out in air, allowing for thermal input by a solar power tower with a windowless, cavity receiver
Hybrid metal oxide cycle water splitting
Hybrid thermochemical water splitting systems are disclosed that thermally reduces metal oxides particles to displace some but not all of the electrical requirements in a water splitting electrolytic cell. In these hybrid systems, the thermal reduction temperature is significantly reduced compared to two-step metal-oxide thermochemical cycles in which only thermal energy is required to produce hydrogen from water. Also, unlike conventional higher temperature systems where the reduction step must be carried out under reduced oxygen pressure, the reduction step in the proposed hybrid systems can be carried out in air, allowing for thermal input by a solar power tower with a windowless, cavity receiver
Experimental characterization of the 4D tensor monopole and topological nodal rings
Quantum mechanics predicts the existence of the Dirac and the Yang monopoles.
Although their direct experimental observation in high-energy physics is still
lacking, these monopoles, together with their associated vector gauge fields,
have been demonstrated in synthetic matter. On the other hand, monopoles in
even-dimensional spaces have proven more elusive. A potential unifying
framework--string theory--that encompasses quantum mechanics promotes the
vector gauge fields to tensor gauge fields, and predicts the existence of more
exotic tensor monopole in 4D space. Here we report the first experimental
observation of a tensor monopole in a 4D parameter space synthesized by the
spin degrees of freedom of a single solid-state defect in diamond. Using two
complementary methods, we reveal the existence of the tensor monopole through
measurements of its quantized topological invariant. By introducing a
fictitious external field that breaks chiral symmetry, we further observe a
novel phase transition to a topological nodal ring semimetal phase that is
protected by mirror symmetries.Comment: main: 10 pages, 4 figures + SI: 22 pages, 27 figure
Interaction-induced lattices for bound states: Designing flat bands, quantized pumps and higher-order topological insulators for doublons
Bound states of two interacting particles moving on a lattice can exhibit
remarkable features that are not captured by the underlying single-particle
picture. Inspired by this phenomenon, we introduce a novel framework by which
genuine interaction-induced geometric and topological effects can be realized
in quantum-engineered systems. Our approach builds on the design of effective
lattices for the center-of-mass motion of two-body bound states
(\emph{doublons}), which can be created through long-range interactions. This
general scenario is illustrated on several examples, where flat-band
localization, topological pumps and higher-order topological corner modes
emerge from genuine interaction effects. Our results pave the way for the
exploration of interaction-induced topological effects in a variety of
platforms, ranging from ultracold gases to interacting photonic devices.Comment: 10 pages,7 figure
Exploring Parity Magnetic Effects through Experimental Simulation with Superconducting Qubits
We present the successful realization of four-dimensional (4D) semimetal
bands featuring tensor monopoles, achieved using superconducting quantum
circuits. Our experiment involves the creation of a highly tunable diamond
energy diagram with four coupled transmons, and the parametric modulation of
their tunable couplers, effectively mapping momentum space to parameter space.
This approach enables us to establish a 4D Dirac-like Hamiltonian with fourfold
degenerate points. Moreover, we manipulate the energy of tensor monopoles by
introducing an additional pump microwave field, generating effective magnetic
and pseudo-electric fields and simulating topological parity magnetic effects
emerging from the parity anomaly. Utilizing non-adiabatic response methods, we
measure the fractional second Chern number for a Dirac valley with a varying
mass term, signifying a nontrivial topological phase transition connected to a
5D Yang monopole. Our work lays the foundation for further investigations into
higher-dimensional topological states of matter and enriches our comprehension
of topological phenomena
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