140 citations · 344 across the 22 of their papers we have counts for
22 papers
Observation of low-lying impurity states in Bose-Einstein condensates
A. M. Morgen, S. S. Balling, M. T. Strøe +6
Impurities embedded in a Bose-Einstein Condensate (BEC) of 39K atoms are investigated with a pump-probe ejection spectroscopy sequence. The spectroscopic signal exhibits a strong f…
Magnetic domains stabilized by symmetry-protected zero modes
Pavel Kos, Dominik S. Wild, Kristian Knakkergaard Nielsen
Understanding mechanisms for the breakdown of thermalization in closed quantum systems is a central problem in quantum many-body physics. We demonstrate strong nonergodic behavior…
Hole and spin dynamics in an anti-ferromagnet close to half filling
Magnus Callsen, Jens H. Nyhegn, Kristian Knakkergaard Nielsen +1
The interplay between charge and spin dynamics is at the heart of strongly correlated materials. Inspired by recent quantum simulation experiments, we develop a conserving diagramm…
Spin-charge bound states and emerging fermions in a quantum spin liquid
Jens H. Nyhegn, Kristian Knakkergaard Nielsen, Leon Balents +1
The complex interplay between charge and spin dynamics lies at the heart of strongly correlated quantum materials, and it is a fundamental topic in basic research with far reaching…
Dual Spectroscopy of Quantum Simulated Fermi-Hubbard Systems
K. Knakkergaard Nielsen, M. Zwierlein, G. M. Bruun
Quantum gas microscopy with atoms in optical lattices provides remarkable insights into the real space properties of many-body systems, but does not directly reveal the nature of t…
Probing a quantum spin liquid with equilibrium and nonequilibrium hole dynamics
J. H. Nyhegn, K. Knakkergaard Nielsen, G. M. Bruun
The properties and experimental identification of quantum spin liquids (QSLs) remain an important topic with many fundamental questions. Here, we explore the dynamics of a single c…
Localized dopant motion across the 2D Ising phase transition
K. Knakkergaard Nielsen
I investigate the motion of a single hole in 2D spin lattices with square and triangular geometries. While the spins have nearest neighbor Ising spin couplings , the hole is all…
Quantum beat spectroscopy of repulsive Bose polarons
A. M. Morgen, S. S. Balling, K. Knakkergaard Nielsen +3
The physics of impurities in a bosonic quantum environment is a paradigmatic and challenging many-body problem that remains to be understood in its full complexity. Here, this prob…
Wave function and spatial structure of polarons in an antiferromagnetic bilayer
Jens H. Nyhegn, Georg M. Bruun, Kristian K. Nielsen
Adding a dopant to an antiferromagnetic spin background disturbs the magnetic order and leads to the formation of a quasiparticle coined the magnetic polaron, which plays a central…
Exact dynamics of two holes in two-leg antiferromagnetic ladders
K. Knakkergaard Nielsen
We study the motion of holes in a mixed-dimensional setup of an antiferromagnetic ladder, featuring nearest neighbor hopping along the ladders and Ising-type spin interactions…
Omnipresent bound state of two holes in antiferromagnetic Bethe lattices
K. Knakkergaard Nielsen
For decades, it has remained an open question, whether two dopants in the -- model bind in the strongly correlated regime of small spin couplings versus hopping, . H…
Holes and magnetic polarons in a triangular lattice antiferromagnet
Jasper van de Kraats, Kristian K. Nielsen, Georg M. Bruun
The intricate interplay between charge motion and magnetic order in geometrically frustrated lattices is central for the properties of many two-dimensional quantum materials. The t…
Equilibrium and non-equilibrium dynamics of a hole in a bilayer antiferromagnet
Jens H. Nyhegn, Kristian K. Nielsen, Georg M. Bruun
The dynamics of charge carriers in lattices of quantum spins is a long standing and fundamental problem. Recently, a new generation of quantum simulation experiments based on atoms…
Exact nonequilibrium hole dynamics, magnetic polarons and string excitations in antiferromagnetic Bethe lattices
K. Knakkergaard Nielsen
We investigate a rare instance of an exactly solvable nonequilibrium many-body problem. In particular, we derive an exact solution for the nonequilibrium dynamics of an initially l…
Life and death of the Bose polaron
Magnus G. Skou, Kristian Knakkergaard Nielsen, Thomas G. Skov +6
Spectroscopic and interferometric measurements complement each other in extracting the fundamental properties of quantum many-body systems. While spectroscopy provides precise meas…
Nonequilibrium Hole Dynamics in Antiferromagnets: Damped Strings and Polarons
K. Knakkergaard Nielsen, T. Pohl, G. M. Bruun
We develop a nonperturbative theory for hole dynamics in antiferromagnetic spin lattices, as described by the - model. This is achieved by generalizing the selfconsistent Bor…
Spatial structure of magnetic polarons in strongly interacting antiferromagnets
K. K. Nielsen, M. A. Bastarrachea-Magnani, T. Pohl +1
The properties of mobile impurities in quantum magnets are fundamental for our understanding of strongly correlated materials and may play a key role in the physics of high-tempera…
Non-equilibrium quantum dynamics and formation of the Bose polaron
Magnus G. Skou, Thomas G. Skov, Nils B. Jørgensen +5
Advancing our understanding of non-equilibrium phenomena in quantum many-body systems remains among the greatest challenges in physics. Here, we report on the experimental observat…
Superfluid flow of polaron polaritons above Landau's critical velocity
K. Knakkergaard Nielsen, A. Camacho-Guardian, G. M. Bruun +1
We develop a theory for the interaction of light with superfluid optical media, describing the motion of quantum impurities that are created and dragged through the liquid by propa…
Polariton dynamics in strongly interacting quantum many-body systems
A. Camacho-Guardian, K. Knakkergaard Nielsen, T. Pohl +1
We develop a theory for light propagating in an atomic Bose-Einstein condensate in the presence of strong interactions. The resulting many-body correlations are shown to have profo…
Critical slowdown of non-equilibrium polaron dynamics
Kristian Knakkergaard Nielsen, Luis A. Peña Ardila, Georg M. Bruun +1
We study the quantum dynamics of a single impurity following its sudden immersion into a Bose-Einstein condensate. The ensuing formation of the Bose polaron in this general setting…
Higher first Chern numbers in one dimensional Bose-Fermi mixtures
Kristian Knakkergaard Nielsen, Zhigang Wu, Georg M. Bruun
We propose to use a one-dimensional system consisting of identical fermions in a periodically driven lattice immersed in a Bose gas, to realise topological superfluid phases with C…