Program

Speaker	Affiliation	Title	Recording
Claus Lämmerzahl	University of Bremen	On the foundations of quantum mechanics
Each fundamental theory of physics has to be tested at best. Quantum mechanics is defined through a set of mainly mathematical postulates which phenomenological richness in terms of physical applications has so far been explored on a modest scale only. The fact that this theory is not based on a constructive approach makes is particularly difficult to introduce in a systematic way modifications which then can be subject to experiments. In this contribution we present and evaluate various modifications of quantum mechanics.
Peter Schupp	Constructor University	Gravity as free fall in graded geometry
Deformations of the algebra of quantum operators lead to a description of fundamental interactions that generalizes and in a sense unifies the principles of gauge theory and the geometric description of gravity as free fall in curved spacetime. This approach is already quite well established for electromagnetism and is for example useful for the description of charged particles in a magnetic monopole background. We shall show that also gravitational interactions find such an algebraic description, but the construction requires a graded (super) geometry setting. The construction suggests a novel somewhat more algebraic interpretation of key ingredients of general relativity. A practical motivation for this line of research is to make methods and results from gauge theory available for gravitational physics. Potential applications include Aharanov-Bohm type (geometric phase) effects for gravitational fields.
Christian Pfeifer	University of Bremen	General Linear Electrodynamics: Causal Structure, Propagators, Quantization and quantum energy inequalities
From an axiomatic point of view, the fundamental input for a theory of electrodynamics are Maxwell’s equations dF=0 (or F=dA) and dH=J, and a constitutive law H=# F, which relates the field strength 2-form F and the excitation 2-form H. In this talk we consider general linear Electrodynamics, the theory of Electrodynamics which is defined through a local and linear constitutive law. The best known application of this theory is the effective description of Electrodynamics inside (linear) media including for example birefringence. We will analyse the classical theory of the electromagnetic potential A thoroughly before we present the quantisation of premetric electrodynamics. The resulting theory of quantum premetric electrodynamics is a well defined relativistic quantum field theory, which is not locally Lorentz invariant. As a specific application of this theory of quantum premetric electrodynamics I will present the derivation of a quantum energy inequality, that is satsified by the energy density of the electromagnetic field averaged along observer wordlines inside a uniaxial crystal. The later is geometrically described by a constitutive law that depends not only on a metric, but in addition on two vector fields describing the crystal's optical axis and rest frame.
Klemens Hammerer	Leibniz University Hannover	Atom interferometers in weakly curved spacetimes using Bragg diffraction and Bloch oscillations
We present a systematic approach to determine all relativistic phases up to O(c−2) in light-pulse atom interferometers in weakly curved spacetime that are based on elastic scattering, namely Bragg diffraction and Bloch oscillations. Our analysis is derived from first principles using the parameterized post-Newtonian (PPN) formalism. In the treatment developed here, we derive algebraic expressions for relativistic phases for arbitrary interferometer (IF) geometries in an automated manner. As case studies, we consider symmetric and antisymmetric Ramsey-Borde interferometers, as well as a symmetric double diffraction interferometer with baseline lengths of 10 m and 100 m. We compare our results to previous calculations conducted for a Mach-Zehnder interferometer.
Philip Schwartz	Leibniz University Hannover	Coupling quantum matter to gravity: a systematic post-Newtonian approach
Modern quantum-optical experiments are close to reaching a precision that will allow for the observation of post-Newtonian effects of gravity in the lab. In recent years, several interesting proposals in this direction have been made; and even if the observation of gravitational effects is not the aim of an experiment, they still have to be taken into account. For such considerations, one needs a well-defined scheme according to which the coupling of quantum matter to the classical gravitational field is determined. Such a scheme needs to be complete (i.e. account for all terms to a given post-Newtonian order), systematic, and generally applicable (i.e. without a priori restrictions on the quantum states of matter). Of course, for full ‘relativistic’ gravity, such a scheme exists in the form of quantum field theory in curved spacetimes (QFTCS). If one is interested in post-Newtonian gravity, however, one can employ an easier approach that is mathematically and conceptually less heavy than full-blown QFTCS, based on systematic post-Newtonian expansions. In this talk, I will motivate this perspective and illustrate it by a brief discussion of two such systematic derivations of post-Newtonian descriptions of quantum systems under gravity: (a) a toy-model ‘atom’ (electromagnetically bound two-particle system) in a static weak gravitational background field, and (b) a massive spin-half particle in the vicinity of a slowly accelerating observer in a general weakly-curved spacetime.
Sven Herrmann	University of Bremen	Cold atom interferometry with extended free fall time – recent progress and ideas
Over the last decade, cold atom interferometry has matured into a sensitive tool that can be applied both for practical applications as well as sensitive tests of fundamental physics. In particular, several long baseline instruments as well as microgravity experiments with access to extended free fall times push the achievable sensitivity into new regimes. This holds the promise to explore the interface of gravity and quantum physics in new and exciting ways. In my talk, I will first present some of our own work on interferometry with extended free fall times in the Bremen drop tower. I then want to discuss some of the recent ideas that have been brought forward to perform test experiments for gravity using interferometry on long baselines and with extended free fall.
Roy Barzel	University of Bremen	Gravitationally induced entanglement dynamics
We investigate the effect of gravitationally induced entanglement dynamics -- the basis of a mechanism of universal decoherence -- for photonic states in a quantum field theoretical framework. We discuss the prospects of witnessing the effect by use of quantum memories and delay lines via Hong-Ou-Mandel interference. This represents a genuine quantum test of general relativity, combining a multi-particle effect predicted by the quantum theory of light and the general relativistic effect of gravitational time dilation.
Dennis Rätzel	University of Bremen	Using optomechanical systems to test gravitational theory - possibilities and limitations
More than 100 years after the first development of a relativistic theory of gravity, there is an ever-increasing amount of predicted, yet untested, phenomena and unsolved scientific puzzles revolving around gravity. There are many proposals to apply quantum sensors to test for such phenomena or experimentally resolve some of the puzzles. In this talk, I will present my perspective on three proposals based on optomechanical systems: measurement of the gravitational field of light and relativistic particle beams, obtaining bounds on Chameleon-field dark energy models, and testing for quantum properties of the gravitational field. I will give a short introduction to the models involved and discuss fundamental constraints.