arXiv subjects

Florian Koch

Publications and source records attributed to Florian Koch.

6 recordsLinked to original sources

arXiv2025

Liouvillian topology and nonreciprocal dynamics in open Floquet chains

Open quantum systems far from thermal equilibrium can exhibit remarkable physical phenomena including topological properties without a direct equilibrium counterpart. Along these lines, in periodically driven-dissipative systems within the effective non-Hermitian (NH) Hamiltonian approximation spectral winding numbers have been linked to intriguing nonreciprocal transport properties. Here, going beyond an NH Hamiltonian description, we introduce and study a microscopic lattice model of a driven open quantum system described by a Markovian quantum master equation, which exhibits the mentioned spectral winding within an NH approximation. By encompassing quantum jump processes in the topological analysis, we uncover a distinct \emph{jump-induced} topological phase, which qualitatively corresponds to the richer nonreciprocal transport properties of the fully quantum model. In addition, we find that the NH skin effect, i.e., the accumulation of a macroscopic number of eigenstates at one end of the system, is already visible in the transient dynamics even for systems with periodic boundary conditions. Our results exemplify the subtle correspondence between NH topological properties and physical manifestations of Liouvillian topological properties in open quantum systems, thus providing a theoretical framework towards understanding unidirectional transport in quantum dissipative Floquet dynamics.

cond-mat.mes-hall↗

arXiv2024

Dissipative frequency converter: from Lindblad dynamics to non-Hermitian topology

A topological frequency converter represents a dynamical counterpart of the integer quantum Hall effect, where a two-level system enacts a quantized time-averaged power transfer between two driving modes of incommensurate frequency. Here, we investigate as to what extent temporal coherence in the quantum dynamics of the two-level system is important for the topological quantization of the converter. To this end, we consider dissipative channels corresponding to spontaneous decay and dephasing in the instantaneous eigenbasis of the Hamiltonian as well as spontaneous decay in a fixed basis. The dissipation is modelled using both a full Lindblad and an effective non-Hermitian (NH) Hamiltonian description. For all three dissipation channels we find a transition from the unperturbed dynamics to a quantum watchdog effect, which destroys any power transfer in the strong coupling limit. This is striking because the watchdog effect leads to perfectly adiabatic dynamics in the instantaneous eigenbasis, at first glance similar to the unperturbed case. Furthermore, it is found that dephasing immediately leads to an exponential decay of the power transfer in time due to loss of polarisation in the mixed quantum state. Finally, we discuss the appearance in the effective NH trajectory description of non-adiabatic processes, which are suppressed in the full Lindblad dynamics.

cond-mat.mes-hall↗

arXiv2022

Quantum Non-Hermitian Topological Sensors

We investigate in the framework of quantum noise theory how the striking boundary-sensitivity recently discovered in the context of non-Hermitian (NH) topological phases may be harnessed to devise novel quantum sensors. Specifically, we study a quantum-optical setting of coupled modes arranged in an array with broken ring geometry that would realize a NH topological phase in the classical limit. Using methods from quantum-information theory of Gaussian states, we show that a small coupling induced between the ends of the broken ring may be detected with a precision that increases exponentially in the number of coupled modes, e.g. by heterodyne detection of two output modes. While this robust effect only relies on reaching a NH topological regime, we identify a resonance phenomenon without direct classical counterpart that provides an experimental knob for drastically enhancing the aforementioned exponential growth. Our findings pave the way towards designing quantum NH topological sensors (QUANTOS) that may observe with high precision any physical observable that couples to the boundary conditions of the device.

quant-ph↗

arXiv2006

Vector Field Twisting of Lie-Algebras

In quantum groups coproducts of Lie-algebras are twisted in terms of generators of the corresponding universal enveloping algebra. If representations are considered, twists also serve as starproducts that accordingly quantize representation spaces. In physics, requirements turn out to be the other way around. Physics comes up with noncommutative spaces in terms of starproducts that miss a suiting quantum symmetry. In general the classical limit is known, i.e. there exists a representation of the Lie-algebra on a corresponding finitely generated commutative space. In this setup quantization can be considered independently from any representation theoretic issue. We construct an algebra of vector fields from a left cross-product algebra of the representation space and its Hopf-algebra of momenta. The latter can always be defined. The suitingly devided cross-product algebra is then lifted to a Hopf-algebra that carries the required genuine structure to accomodate a matrix representation of the universal enveloping algebra as a subalgebra. We twist the Hopf-algebra of vector fields and thereby obtain the desired twisting of the Lie-algebra. Since we twist with vector fields and not with generators of the Lie-algebra, this is the most general twisting that can possibly be obtained. In other words, we push starproducts to twists of the desired symmetry algebra and to this purpose solve the problem of turning vector fields into a Hopf-algebra. We give some genuine example.

hep-th↗

arXiv2006

Twist-Deformed Lorentzian Heisenberg-Algebras

The Moyal-Weyl quantization procedure is embedded into the twist formalism of vector fields on phase space. Double application of twists provide most general deformations of Minkowskian Heisenberg-algebras and corresponding quantizations of the Lorentz-algebra. Such deformations deliver high-energy extensions of standard relativistic quantum mechanics. These are required to obtain minimal uncertainty properties for high-energy spacetime measurements that standard quantum mechanics lacks. The procedure of double twist application is outlined. We give an instructive and genuine example.

hep-th↗

arXiv2004

Construction of $θ$-Poincaré Algebras and their Invariants on $\mathcal{M}_θ$

In the present paper we construct deformations of the Poincaré algebra as representations on a noncommutative spacetime with canonical commutation relations. These deformations are obtained by solving a set of conditions by an appropriate ansatz for the deformed Lorentz generator. They turn out to be Hopf algebras of quantum universal enveloping algebra type with nontrivial antipodes. In order to present a notion of $θ$-deformed Minkowski space $\mathcal{M}_θ$, we introduce Casimir operators and spacetime invariants for all deformations obtained.

hep-th↗