arXiv subjects

Hannes Busche

Publications and source records attributed to Hannes Busche.

9 recordsLinked to original sources

arXiv2026

QCI Connect: A Modular Full-Stack Quantum Computing Platform

In a world of various competing quantum computing architectures, hardware-agnostic, full-stack platforms are necessary to bring the full power of quantum computing hardware to domain experts via the cloud. QCI Connect and its Software Development Kit provide a reference architecture for a full-stack platform with a modular design and open-source interface definitions, built to facilitate a community-driven application ecosystem. Here, we present its overall design and features, central interfaces, and lessons learned, both for users of the platform and as a reference guide for future developments.

quant-ph↗

arXiv2024

Nonreciprocal recovery of electromagnetically induced transparency by wavenumber mismatch in hot atoms

For multi-level systems in hot atomic vapors the interplay between the Doppler shift due to atom velocity and the wavenubmer mismatch between driving laser fields strongly influences transmission and absorption properties of the atomic medium. In a three-level atomic ladder-system, Doppler broadening limits the visibility of electromagnetically-induced transparency (EIT) when the probe and control fields are co-propagating, while EIT is recovered under the opposite condition of counter-propagating geometry and $k_{p} < k_{c}$, with $k_{p}$ and $k_{c}$ being the wavenumbers of the probe and control fields, respectively. This effect has been studied and experimentally demonstrated as an efficient mechanism to realize non-reciprocal probe light transmission, opening promising avenues for example for realization of magnetic-field free optical isolators. In this tutorial we discuss the theoretical derivation of this effect and show the underlying mechanism to be an avoided crossing of the states dressed by the coupling laser as a function of atomic velocities when $k_{p}<k_{c}$. We investigate how the non-reciprocity scales with wavelength mismatch and show how to experimentally demonstrate the effect in a simple Rydberg-EIT system using thermal Rubidium atoms.

quant-ph↗

arXiv2022

Creation of non-classical states of light in a chiral waveguide

Creating non-classical states of light from simple quantum systems together with classical resources is a challenging problem. We show how chiral emitters under a coherent drive can generate non-classical photon states. For our analysis, we select a specific temporal mode in the transmitted light field, resulting in a coupled master equation for the relevant mode and the chiral emitters. We characterise the mode's state by its Wigner function and show that the emission from the system predominantly produces mixtures of few-photon-added coherent states. We argue that these non-classical states are experimentally accessible and show their application for quantum metrology.

quant-ph↗

arXiv2021

Epidemic spreading and herd immunity in a driven non-equilibrium system of strongly-interacting atoms

It is increasingly important to understand the spatial dynamics of epidemics. While there are numerous mathematical models of epidemics, there is a scarcity of physical systems with sufficiently well-controlled parameters to allow quantitative model testing. It is also challenging to replicate the macro non-equilibrium effects of complex models in microscopic systems. In this work, we demonstrate experimentally a physics analog of epidemic spreading using optically driven non-equilibrium phase transitions in strongly interacting Rydberg atoms. Using multiple laser beams we can impose any desired spatial structure. We observe spatially localized phase transitions and their interplay in different parts of the sample. These phase transitions simulate the outbreak of an infectious disease in multiple locations, as well as the dynamics towards herd immunity and endemic state in different regimes. The reported results indicate that Rydberg systems are versatile enough to model complex spatial-temporal dynamics.

quant-ph↗

arXiv2021

Controlled multi-photon subtraction with cascaded Rydberg superatoms as single-photon absorbers

The preparation of light pulses with well-defined quantum properties requires precise control at the individual photon level. Here, we demonstrate exact and controlled multi-photon subtraction from incoming light pulses. We employ a cascaded system of tightly confined cold atom ensembles with strong, collectively enhanced coupling of photons to Rydberg states. The excitation blockade resulting from interactions between Rydberg atoms limits photon absorption to one per ensemble and engineered dephasing of the collective excitation suppresses stimulated re-emission of the photon. We experimentally demonstrate subtraction with up to three absorbers. Furthermore, we present a thorough theoretical analysis of our scheme where we identify weak Raman decay of the long-lived Rydberg state as the main source of infidelity in the subtracted photon number. We show that our scheme should scale well to higher absorber numbers if the Raman decay can be further suppressed.

quant-ph↗

arXiv2020

Non-exponential decay of a collective excitation in an atomic ensemble coupled to a one-dimensional waveguide

We study the dynamics of a single excitation coherently shared amongst an ensemble of atoms and coupled to a one-dimensional wave guide. The coupling between the matter and the light field gives rise to collective phenomena such as superradiant states with an enhanced initial decay rate, but also to the coherent exchange of the excitation between the atoms. We find that the competition between the two phenomena provides a characteristic dynamics for the decay of the excitations, and remarkably exhibits an algebraic behavior, instead of the expected standard exponential one, for a large number of atoms. The analysis is first performed for a chiral waveguide, where the problem can be solved analytically, and then is extended to the bidirectional waveguide.

quant-ph↗

arXiv2020

Observation of collective decay dynamics of a single Rydberg superatom

We experimentally investigate the collective decay of a single Rydberg superatom, formed by an ensemble of thousands of individual atoms supporting only a single excitation due to the Rydberg blockade. Instead of observing a constant decay rate determined by the collective coupling strength to the driving field, we show that the enhanced emission of the single stored photon into the forward direction of the coupled optical mode depends on the dynamics of the superatom before the decay. We find that the observed decay rates are reproduced by an expanded model of the superatom which includes coherent coupling between the collective bright state and subradiant states.

quant-ph↗

arXiv2020

Collective Mode Interferences in Light--Matter Interactions

We present a theoretical and experimental analysis of transient optical properties of a dense cold atomic gas. After the rapid extinction of a weak coherent driving field (mean photon number $\sim 1.5$), a transient `flash' is observed. Surprisingly the decay of the `flash' is faster than the decay of the fastest superradiant mode of the system. We show that this `faster than superradiance decay' is expected due to the interference between collective eigenmodes that exhibit a range of frequency shifts away from the bare atomic transition. Experimental results confirm that the initial decay rate of the superradiant flash increases with optical depth, in agreement with the numerical simulations for the experimental conditions.

physics.atom-ph↗

arXiv2020

Phase diagram and self-organising dynamics in a strongly-interacting thermal Rydberg ensemble

Abstract Far-from equilibrium dynamics that lead to self-organization are highly relevant to complex dynamical systems not only in physics, but also in life-, earth-, and social sciences. It is challenging however to find systems with sufficiently controllable parameters that allow quantitatively modelling of emergent properties. Here, we study a non-equilibrium phase transition and observe signatures of self-organized criticality in a dilute thermal vapour of atoms optically excited to strongly interacting Rydberg states. Electromagnetically induced transparency (EIT) provides excellent control over the population dynamics and enables high-resolution probing of the driven-dissipative dynamics, which also exhibits phase bistability. Increased sensitivity compared to previous work allows us to reconstruct the complete phase diagram including in the vicinity of the critical point. We observe that interaction-induced energy shifts and enhanced decay only occur in one of the phases above a critical Rydberg population. This limits the application of generic mean-field models, however a modified, threshold-dependent approach is in qualitative agreement with experimental data. Near threshold, we observe self-organized dynamics in the form of population jumps that return the density to a critical value.

physics.atom-ph↗