arXiv subjects

Markus K. Oberthaler

Publications and source records attributed to Markus K. Oberthaler.

At least 37 records · Page 2Linked to original sources

arXiv2022

Curved and expanding spacetime geometries in Bose-Einstein condensates

Phonons have the characteristic linear dispersion relation of massless relativistic particles. They arise as low energy excitations of Bose-Einstein condensates and, in nonhomogeneous situations, are governed by a space- and time-dependent acoustic metric. We discuss how this metric can be experimentally designed to realize curved spacetime geometries, in particular, expanding Friedmann-Lemaître-Robertson-Walker cosmologies, with negative, vanishing, or positive spatial curvature. A nonvanishing Hubble rate can be obtained through a time-dependent scattering length of the background condensate. For relativistic quantum fields this leads to the phenomenon of particle production, which we describe in detail. We explain how particle production and other interesting features of quantum field theory in curved spacetime can be tested in terms of experimentally accessible correlation functions.

cond-mat.quant-gas↗

arXiv2021

Spiking neuromorphic chip learns entangled quantum states

The approximation of quantum states with artificial neural networks has gained a lot of attention during the last years. Meanwhile, analog neuromorphic chips, inspired by structural and dynamical properties of the biological brain, show a high energy efficiency in running artificial neural-network architectures for the profit of generative applications. This encourages employing such hardware systems as platforms for simulations of quantum systems. Here we report on the realization of a prototype using the latest spike-based BrainScaleS hardware allowing us to represent few-qubit maximally entangled quantum states with high fidelities. Bell correlations of pure and mixed two-qubit states are well captured by the analog hardware, demonstrating an important building block for simulating quantum systems with spiking neuromorphic chips.

cs.ET↗

arXiv2021

Finding self-similar behavior in quantum many-body dynamics via persistent homology

Inspired by topological data analysis techniques, we introduce persistent homology observables and apply them in a geometric analysis of the dynamics of quantum field theories. As a prototype application, we consider data from a classical-statistical simulation of a two-dimensional Bose gas far from equilibrium. We discover a continuous spectrum of dynamical scaling exponents, which provides a refined classification of nonequilibrium self-similar phenomena. A possible explanation of the underlying processes is provided in terms of mixing strong wave turbulence and anomalous vortex kinetics components in point clouds. We find that the persistent homology scaling exponents are inherently linked to the geometry of the system, as the derivation of a packing relation reveals. The approach opens new ways of analyzing quantum many-body dynamics in terms of robust topological structures beyond standard field theoretic techniques.

cond-mat.quant-gas↗

arXiv2021

Analog cosmological reheating in an ultracold Bose gas

Cosmological reheating describes the transition of the post-inflationary universe to a hot and thermal state. In order to shed light on the underlying dynamics of this process, we propose to quantum-simulate the reheating-like dynamics of a generic cosmological single-field model in an ultracold Bose gas. In our setup, the excitations on top of an atomic Bose-Einstein condensate play the role of the particles produced by the decaying inflaton field after inflation. Expanding spacetime as well as the background oscillating inflaton field are mimicked in the non-relativistic limit by a time dependence of the atomic interactions, which can be tuned experimentally via Feshbach resonances. As we illustrate by means of classical-statistical simulations for the case of two spatial dimensions, the dynamics of the atomic system exhibits the characteristic stages of far-from-equilibrium reheating, including the amplification of fluctuations via parametric instabilities and the subsequent turbulent transport of energy towards higher momenta. The transport is governed by a non-thermal fixed point showing universal self-similar time evolution as well as a transient regime of prescaling with time-dependent scaling exponents. While the classical-statistical simulations can capture only the earlier stages of the dynamics for weak couplings, the proposed experiment has the potential of exploring the evolution up to late times even beyond the weak coupling regime.

cond-mat.quant-gas↗

arXiv2021

High signal to noise absorption imaging of alkali atoms at moderate magnetic fields

We present an improved scheme for absorption imaging of alkali atoms at moderate magnetic fields, where the excited state is well in the Paschen-Back regime but the ground state hyperfine manifold is not. It utilizes four atomic levels to obtain an approximately closed optical cycle. With the resulting absorption of the corresponding two laser frequencies we extract the atomic column density of a $^{39}$K Bose-Einstein condensate. The scheme can be readily applied to all other alkali-like species.

cond-mat.quant-gas↗

arXiv2020

Collisions of three-component vector solitons in Bose-Einstein condensates

Ultracold gases provide an unprecedented level of control for the investigation of soliton dynamics and collisions. We present a scheme for deterministically preparing pairs of three-component solitons in a Bose-Einstein condensate. Our method is based on local spin rotations which simultaneously imprint suitable phase and density distributions. This enables us to observe striking collisional properties of the vector degree of freedom which naturally arises for the coherent nature of the emerging multi-component solitons. We find that the solitonic properties in the quasi-one-dimensional system are quantitatively described by the integrable repulsive three-component Manakov model.

cond-mat.quant-gas↗

arXiv2019

Realizing a scalable building block of a U(1) gauge theory with cold atomic mixtures

In the fundamental laws of physics, gauge fields mediate the interaction between charged particles. An example is quantum electrodynamics -- the theory of electrons interacting with the electromagnetic field -- based on U(1) gauge symmetry. Solving such gauge theories is in general a hard problem for classical computational techniques. While quantum computers suggest a way forward, it is difficult to build large-scale digital quantum devices required for complex simulations. Here, we propose a fully scalable analog quantum simulator of a U(1) gauge theory in one spatial dimension. To engineer the local gauge symmetry, we employ inter-species spin-changing collisions in an atomic mixture. We demonstrate the experimental realization of the elementary building block as a key step towards a platform for large-scale quantum simulations of continuous gauge theories.

cond-mat.quant-gas↗

arXiv2019

Experimental extraction of the quantum effective action for a non-equilibrium many-body system

Far-from-equilibrium situations are ubiquitous in nature. They are responsible for a wealth of phenomena, which are not simple extensions of near-equilibrium properties, ranging from fluid flows turning turbulent to the highly organized forms of life. On the fundamental level, quantum fluctuations or entanglement lead to novel forms of complex dynamical behaviour in many-body systems for which a description as emergent phenomena can be found within the framework of quantum field theory. A central quantity in these efforts, containing all information about the measurable physical properties, is the quantum effective action. Though the problem of non-equilibrium quantum dynamics can be exactly formulated in terms of the quantum effective action, the solution is in general beyond capabilities of classical computers. In this work, we present a strategy to determine the non-equilibrium quantum effective action using analog quantum simulators, and demonstrate our method experimentally with a quasi one-dimensional spinor Bose gas out of equilibrium. Building on spatially resolved snapshots of the spin degree of freedom, we infer the quantum effective action up to fourth order in an expansion in one-particle irreducible correlation functions at equal times. We uncover a strong suppression of the irreducible four-vertex emerging at low momenta, which solves the problem of dynamics in the highly occupied regime far from equilibrium where perturbative descriptions fail. Similar behaviour in this non-pertubative regime has been proposed in the context of early-universe cosmology. Our work constitutes a new realm of large-scale analog quantum computing, where the high level of control of synthetic quantum systems provides the means for the solution of long-standing theoretical problems in high-energy and condensed matter physics with an experimental approach.

cond-mat.quant-gas↗

arXiv2019

Simultaneous Readout of Noncommuting Collective Spin Observables beyond the Standard Quantum Limit

We augment the information extractable from a single absorption image of a spinor Bose-Einstein condensate by coupling to initially empty auxiliary hyperfine states. Performing unitary transformations in both, the original and auxiliary hyperfine manifold, enables the simultaneous measurement of multiple spin-1 observables. We apply this scheme to an elongated atomic cloud of $ ^{87} $Rb to simultaneously read out three orthogonal spin directions and with that directly access the spatial spin structure. The readout even allows the extraction of quantum correlations which we demonstrate by detecting spin nematic squeezing without state tomography.

cond-mat.quant-gas↗

arXiv2018

Bi-directional universal dynamics in a spinor Bose gas close to a non-thermal fixed point

We numerically study the universal scaling dynamics of an isolated one-dimensional ferromagnetic spin-1 Bose gas. Preparing the system in a far-from-equilibrium initial state, simultaneous coarsening and refining is found to enable and characterize the approach to a non-thermal fixed point. A macroscopic length scale which scales in time according to $L_Λ(t)\sim t^{\, β}$, with $β\simeq 1/4$, quantifies the coarsening of the size of spin textures. At the same time kink-like defects populating these textures undergo a refining process measured by a shrinking microscopic length scale $L_λ\sim t^{\, β'}$, with $β'\simeq-0.17$. The combination of these scaling evolutions enables particle and energy conservation in the isolated system and constitutes a bi-directional transport in momentum space. The value of the coarsening exponent $β$ suggests the dynamics to belong to the universality class of diffusive coarsening of the one-dimensional XY-model. However, the universal momentum distribution function exhibiting non-linear transport marks the distinction between diffusive coarsening and the approach of a non-thermal fixed point in the isolated system considered here. This underlines the importance of the universal scaling function in classifying non-thermal fixed points. Present-day experiments with quantum gases are expected to have access to the predicted bi-directional scaling.

cond-mat.quant-gas↗

arXiv2018

Observation of universal dynamics in a spinor Bose gas far from equilibrium

The dynamics of quantum systems far from equilibrium represents one of the most challenging problems in theoretical many-body physics. While the evolution is in general intractable in all its details, relevant observables can become insensitive to microscopic system parameters and initial conditions. This is the basis of the phenomenon of universality. Far from equilibrium, universality is identified through the scaling of the spatiotemporal evolution of the system, captured by universal exponents and functions. Theoretically, this has been studied in examples as different as the reheating process in inflationary universe cosmology, the dynamics of nuclear collision experiments described by quantum chromodynamics, or the post-quench dynamics in dilute quantum gases in non-relativistic quantum field theory. Here we observe the emergence of universal dynamics by evaluating spatially resolved spin correlations in a quasi one-dimensional spinor Bose-Einstein condensate. For long evolution times we extract the scaling properties from the spatial correlations of the spin excitations. From this we find the dynamics to be governed by transport of an emergent conserved quantity towards low momentum scales. Our results establish an important class of non-stationary systems whose dynamics is encoded in time independent scaling exponents and functions signaling the existence of non-thermal fixed points. We confirm that the non-thermal scaling phenomenon involves no fine-tuning, by preparing different initial conditions and observing the same scaling behaviour. Our analog quantum simulation approach provides the basis to reveal the underlying mechanisms and characteristics of non-thermal universality classes. One may use this universality to learn, from experiments with ultra-cold gases, about fundamental aspects of dynamics studied in cosmology and quantum chromodynamics.

cond-mat.quant-gas↗

arXiv2018

Dating glacier ice of the last millennium by quantum technology

Radiometric dating with 39Ar covers a unique timespan and offers key advances in interpreting environmental archives of the last millennium. Although this tracer has been acknowledged for decades, studies so far have been limited by the low abundance and radioactivity, thus requiring huge sample sizes. Atom Trap Trace Analysis, an application of techniques from quantum physics such as laser cooling and trapping, allows to reduce the sample volume by several orders of magnitude, compared to conventional techniques. Here we show that the adaptation of this method to 39Ar is now available for glaciological applications, by demonstrating the first Argon Trap Trace Analysis (ArTTA) dating of alpine glacier ice samples. Ice blocks as small as a few kilograms are sufficient and have been obtained at two artificial glacier caves. Importantly, both sites offer direct access to the stratigraphy at the glacier base and validation against existing age constraints. The ice blocks obtained at Chli Titlis glacier in 3030 m all (Swiss Alps) have been dated by state-of-the-art micro-radiocarbon analysis in a previous study. The unique finding of a bark fragment and a larch needle within the ice of Schaufelferner glacier in 2870 m asl (Stubai Alps, Austria) allows for conventional radiocarbon dating. At both sites, results of 39Ar dating match the existing age information based on radiocarbon dating and visual stratigraphy. With our results, we establish Argon Trap Trace Analysis as the key to decipher so far untapped glacier archives of the last millennium.

physics.app-ph↗

arXiv2018

Quantum metrology with nonclassical states of atomic ensembles

Quantum technologies exploit entanglement to revolutionize computing, measurements, and communications. This has stimulated the research in different areas of physics to engineer and manipulate fragile many-particle entangled states. Progress has been particularly rapid for atoms. Thanks to the large and tunable nonlinearities and the well developed techniques for trapping, controlling and counting, many groundbreaking experiments have demonstrated the generation of entangled states of trapped ions, cold and ultracold gases of neutral atoms. Moreover, atoms can couple strongly to external forces and light fields, which makes them ideal for ultra-precise sensing and time keeping. All these factors call for generating non-classical atomic states designed for phase estimation in atomic clocks and atom interferometers, exploiting many-body entanglement to increase the sensitivity of precision measurements. The goal of this article is to review and illustrate the theory and the experiments with atomic ensembles that have demonstrated many-particle entanglement and quantum-enhanced metrology.

quant-ph↗

arXiv2018

Universal equilibrium scaling functions at short times after a quench

By analyzing spin-spin correlation functions at relatively short distances, we show that equilibrium near-critical properties can be extracted at short times after quenches into the vicinity of a quantum critical point. The time scales after which equilibrium properties can be extracted are sufficiently short so that the proposed scheme should be viable for quantum simulators of spin models based on ultracold atoms or trapped ions. Our results, analytic as well as numeric, are for one-dimensional spin models, either integrable or nonintegrable, but we expect our conclusions to be valid in higher dimensions as well.

cond-mat.stat-mech↗

arXiv2017

Spatially distributed multipartite entanglement enables Einstein-Podolsky-Rosen steering of atomic clouds

A key resource for distributed quantum-enhanced protocols is entanglement between spatially separated modes. Yet, the robust generation and detection of nonlocal entanglement between spatially separated regions of an ultracold atomic system remains a challenge. Here, we use spin mixing in a tightly confined Bose-Einstein condensate to generate an entangled state of indistinguishable particles in a single spatial mode. We show experimentally that this local entanglement can be spatially distributed by self-similar expansion of the atomic cloud. Spatially resolved spin read-out is used to reveal a particularly strong form of quantum correlations known as Einstein-Podolsky-Rosen steering between distinct parts of the expanded cloud. Based on the strength of Einstein-Podolsky-Rosen steering we construct a witness, which testifies up to genuine five-partite entanglement.

cond-mat.quant-gas↗

arXiv2017

Bichromatic force on metastable Argon for Atom Trap Trace Analysis

For an efficient performance of Atom Trap Trace Analysis, it is important to collimate the particles emitted from an effusive source. Their high velocity limits the interaction time with the cooling laser. Therefore forces beyond the limits of the scattering force are desirable. The bichromatic force is a promising candidate for this purpose which is demonstrated here for the first time on metastable argon-40. The precollimated atoms are detected in one dimension and the acquired Doppler shift is detected by absorption spectroscopy. With the experimentally accessible parameters, it was possible to measure a force three times stronger than the scattering force. Systematic studies on its dependence on Rabi frequency, phase difference and detuning to atomic resonance are comparedto the solution of the optical Bloch equations. We anticipate predictions for a possible application in Atom Trap Trace Analysis of argon-39 and other noble gas experiments, where a high flux of metastable atoms is needed.

physics.atom-ph↗

arXiv2016

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

We experimentally demonstrate a nonlinear detection scheme exploiting time-reversal dynamics that disentangles continuous variable entangled states for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is used as the nonlinear mechanism which not only generates entangled states but can also be time reversed by controlled phase imprinting. For demonstration of a quantum-enhanced measurement we construct an active atom SU(1,1) interferometer, where entangled state preparation and nonlinear readout both consist of parametric amplification. This scheme is capable of exhausting the quantum resource by detecting solely mean atom numbers. Controlled nonlinear transformations widen the spectrum of useful entangled states for applied quantum technologies.

cond-mat.quant-gas↗

arXiv2015

Observation of scaling in the dynamics of a strongly quenched quantum gas

We report on the experimental observation of scaling in the time evolution following a sudden quench into the vicinity of a quantum critical point. The experimental system, a two-component Bose gas with coherent exchange between the constituents, allows for the necessary high level of control of parameters as well as the access to time-resolved spatial correlation functions. The theoretical analysis reveals that when quenching the system close to the critical point, the energy introduced by the quench leads to a short-time evolution exhibiting crossover reminiscent of the finite-temperature critical properties in the system's universality class. Observing the time evolution after a quench represents a paradigm shift in accessing and probing experimentally universal properties close to a quantum critical point and allows in a new way benchmarking of quantum many-body theory with experiments.

cond-mat.quant-gas↗