arXiv subjects

Christoph Nölle

Publications and source records attributed to Christoph Nölle.

12 recordsLinked to original sources

arXiv2024

Semi-classical Schrödinger numerics in the residual representation

The numerical treatment of quantum mechanics in the semi-classical regime is known to be computationally demanding, due to the highly oscillatory behaviour of the wave function and its large spatial extension. A recently proposed representation of quantum mechanics as a residual theory on top of classical Hamiltonian mechanics transforms a semi-classical wave function into a slowly-fluctuating, spatially confined residual wave function. This representation is therefore well-suited for the numerical solution of semi-classical quantum problems. In this note I outline the formulation of the theory and demonstrate its applicability to a set of semi-classical scenarios, including a discussion of limitations. I work out the connection to established numerical approaches, such as the Gaussian beam approximation and the Gaussian wave packet transform by Russo and Smereka. A prototypical implementation of the method has been published as open-source software.

quant-ph↗

arXiv2023

Timeseries on IIoT Platforms: Requirements and Survey for Digital Twins in Process Industry

In the pursue for sustainability in process industry, digital twins necessitate the communication and storage of timeseries data about Industrial Internet of Things (IIoT). Regarding timeseries, this paper first presents a set of requirements specific to process industries. Then, it surveys how existing IIoT technologies meet the requirements. The technologies include the API specifications Asset Administration Shell (AAS), Digital Twin Definition Language (DTDL), NGSI-LD and Open Platform Communications Unified Architecture (OPC UA) as well as six commercial platforms. All the technologies leave significant gaps regarding the requirements, which means that tailor-made extensions are necessary.

cs.SE↗

arXiv2021

Phase space trajectories in quantum mechanics

An adapted representation of quantum mechanics sheds new light on the relationship between quantum states and classical states. In this approach the space of quantum states splits into a product of the state space of classical mechanics and a Hilbert space, and expectation values of observables decompose into their classical value plus a quantum correction. The splitting is preserved under time evolution of the Schrödinger equation under certain assumptions, and the time evolution of the classical part of a quantum state is governed by Hamilton's equation. The new representation is obtained from the usual Hilbert space representation of quantum mechanics by introducing a gauge degree of freedom in a time-dependent unitary transformation, followed by a non-conventional gauge fixing condition.

hep-th↗

arXiv2012

Instantons, five-branes and fractional strings

In this note I review the construction of higher-dimensional instantons and heterotic NS5-branes on Ricci-flat cones from arXiv:1109.3552, as well as fractional strings from arXiv:1202.5046. The focus is on methods and interpretation. I show, furthermore, that smeared 5-brane supergravity solutions on manifolds with holonomy G2 or Spin(7) can be obtained quite generally by a conformal deformation of the Ricci-flat metric, whereas Calabi-Yau and hyperkähler manifolds require more sophisticated deformations and a case by case treatment.

hep-th↗

arXiv2012

Heterotic string plus five-brane systems with asymptotic AdS3

We present NS1+NS5-brane solutions of heterotic supergravity on curved geometries. They interpolate between a near horizon AdS3 x X^k x T^{7-k} region and R^{1,1} x c(X^k) x T^{7-k}, where X^k (with k = 3,5,6,7) is a k-dimensional geometric Killing spinor manifold, c(X^k) its Ricci-flat cone and T^{7-k} a (7-k)-torus. The solutions require first order alpha'-corrections to the field equations, and special point-like instantons play an important role, whose singular support is a calibrated submanifold wrapped by the NS5-brane. It is also possible to add a gauge anti-5-brane. We determine the super isometries of the near horizon geometry which are supposed to appear as symmetries of the holographically dual two-dimensional conformal field theory.

hep-th↗

arXiv2011

Instantons and Killing spinors

We investigate instantons on manifolds with Killing spinors and their cones. Examples of manifolds with Killing spinors include nearly Kaehler 6-manifolds, nearly parallel G_2-manifolds in dimension 7, Sasaki-Einstein manifolds, and 3-Sasakian manifolds. We construct a connection on the tangent bundle over these manifolds which solves the instanton equation, and also show that the instanton equation implies the Yang-Mills equation, despite the presence of torsion. We then construct instantons on the cones over these manifolds, and lift them to solutions of heterotic supergravity. Amongst our solutions are new instantons on even-dimensional Euclidean spaces, as well as the well-known BPST, quaternionic and octonionic instantons.

hep-th↗

arXiv2011

Yang-Mills instantons on cones and sine-cones over nearly Kähler manifolds

We present a unified eight-dimensional approach to instanton equations on several seven-dimensional manifolds associated to a six-dimensional homogeneous nearly Kähler manifold. The cone over the sine-cone on a nearly Kähler manifold has holonomy group Spin(7) and can be foliated by submanifolds with either holonomy group G_2, a nearly parallel G_2-structure or a cocalibrated G_2-structure. We show that there is a G_2-instanton on each of these seven-dimensional manifolds which gives rise to a Spin(7)-instanton in eight dimensions. The well-known octonionic instantons on R^7 and R^8 are contained in our construction as the special cases of an instanton on the cone and on the cone over the sine-cone, both over the six-sphere, respectively.

hep-th↗

arXiv2011

Quantum mechanics and classical trajectories

The classical limit $\hbar$->0 of quantum mechanics is known to be delicate, in particular there seems to be no simple derivation of the classical Hamilton equation, starting from the Schrödinger equation. In this paper I elaborate on an idea of M. Reuter to represent wave functions by parallel sections of a flat vector bundle over phase space, using the connection of Fedosov's construction of deformation quantization. This generalizes the ordinary Schrödinger representation, and allows naturally for a description of quantum states in terms of a curve plus a wave function. Hamilton's equation arises in this context as a condition on the curve, ensuring the dynamics to split into a classical and a quantum part.

math-ph↗

arXiv2011

Homogeneous heterotic supergravity solutions with linear dilaton

I construct solutions to the heterotic supergravity BPS-equations on products of Minkowski space with a non-symmetric coset. All of the bosonic fields are homogeneous and non-vanishing, the dilaton being a linear function on the non-compact part of spacetime.

hep-th↗

arXiv2010

Heterotic compactifications on nearly Kähler manifolds

We consider compactifications of heterotic supergravity on anti-de Sitter space, with a six-dimensional nearly K"ahler manifold as the internal space. Completing the model proposed by Frey and Lippert with the particular choice of SU(3)/U(1)xU(1) for the internal manifold, we show that it satisfies not only the supersymmetry constraints but also the equations of motion with string corrections of order alpha'. Furthermore, we present a non-supersymmetric model. In both solutions we find confirmed a recent result of Ivanov on the connection used for anomaly cancellation. Interestingly, the volume of the internal space is fixed by the supersymmetry constraints and/or the equations of motion.

hep-th↗

arXiv2009

Geometric and deformation quantization

We present a simple geometric construction linking geometric to deformation quantization. Both theories depend on some apparently arbitrary parameters, most importantly a polarization and a symplectic connection, and for real polarizations we find a compatibility condition restricting the set of admissible connections. In the special case when phase space is a cotangent bundle this compatibility condition has many solutions, and the resulting quantum theory not only reproduces the well-known geometric quantization scheme, but also allows to quantize all interesting observables. For Kähler manifolds there is no compatibility condition, but a canonical choice for the parameters. The explicit form of the observables however remains undetermined.

math-ph↗

arXiv2008

On the relation between geometric and deformation quantization

In this paper we investigate the possibility of constructing a complete quantization procedure consisting of geometric and deformation quantization. The latter assigns a noncommutative algebra to a symplectic manifold, by deforming the ordinary pointwise product of functions, whereas geometric quantization is a prescription for the construction of a Hilbert space and a few quantum operators, starting from a symplectic manifold. We determine under which conditions it is possible to define a representation of the deformed algebra on this Hilbert space, thereby to extend the small class of quantizable observables in geometric quantization to all smooth functions, as well as to give a natural representation of the algebra. In particular we look at the special cases of a cotangent bundle and a Kähler manifold.

math-ph↗