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Programmable cavity QED with a fiber-integrated atomic array
Authors:
Stephan Roschinski,
Johannes Schabbauer,
Franz von Silva-Tarouca,
Marvin Holten,
Damien Bloch,
Julian Léonard
Abstract:
Strong atom-photon interactions in optical cavities are a key resource for quantum information processing, quantum networking, and the exploration of quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer arra…
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Strong atom-photon interactions in optical cavities are a key resource for quantum information processing, quantum networking, and the exploration of quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer array with a high-cooperativity fiber Fabry-Pérot microcavity. The array is positioned within the cavity mode and individual sites are controlled with subwavelength precision, enabling continuous tuning of the single-atom coupling strength via deterministic displacement through the standing-wave field. For up to five atoms coupled to the cavity, we measure collectively enhanced vacuum Rabi splitting and implement cavity-based non-destructive readout of the number of coupled atoms. These results establish a scalable architecture for cavity-mediated entanglement generation and many-body cavity QED with single-atom control, and they lay the foundation for fiber-integrated quantum network nodes.
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Submitted 20 August, 2026;
originally announced August 2026.
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High-Speed NV Ensemble Magnetic Field Imaging via Laser Raster Scanning
Authors:
Luca Troise,
Nikolaj W. Hansen,
Marvin Holten,
Dhiren M. Kara,
Jean-Francois Perrier,
Ulrik L. Andersen,
Alexander Huck
Abstract:
We present a technique that uses an ensemble of nitrogen-vacancy (NV) centers in diamond to image magnetic fields with high spatio-temporal resolution and sensitivity. A focused laser beam is raster-scanned using an acousto-optic deflector (AOD) and NV center fluorescence is read out with a single photodetector, enabling low-noise detection with high dynamic range. The method operates in a previou…
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We present a technique that uses an ensemble of nitrogen-vacancy (NV) centers in diamond to image magnetic fields with high spatio-temporal resolution and sensitivity. A focused laser beam is raster-scanned using an acousto-optic deflector (AOD) and NV center fluorescence is read out with a single photodetector, enabling low-noise detection with high dynamic range. The method operates in a previously unexplored regime, quasi-continuous-wave optically detected magnetic resonance (qCW-ODMR). In this regime, NV centers experience short optical pump pulses for spin readout and repolarization -- analogous to pulsed ODMR -- while the microwave field continuously drives the spin transitions. We systematically characterize this regime and show that the spin response is governed by a tunable interplay between coherent evolution and relaxation, determined by the temporal spacing between pump laser pulses. Notably, the technique does not require precise microwave pulse control, thus simplifying experimental implementation. To demonstrate its capabilities, we image time-varying magnetic fields from a microwire with sub-millisecond temporal resolution. This approach enables flexible spatial sampling and, with our diamond, achieves $\text{nT}/\sqrt{\text{Hz}}$-level per-pixel sensitivity, making it well suited for detecting weak, dynamic magnetic fields in biological and other complex systems.
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Submitted 17 December, 2025; v1 submitted 1 December, 2025;
originally announced December 2025.
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Emergent interaction-driven elliptic flow of few fermionic atoms
Authors:
Sandra Brandstetter,
Philipp Lunt,
Carl Heintze,
Giuliano Giacalone,
Lars H. Heyen,
Maciej Gałka,
Keerthan Subramanian,
Marvin Holten,
Philipp M. Preiss,
Stefan Floerchinger,
Selim Jochim
Abstract:
Hydrodynamics provides a successful framework to effectively describe the dynamics of complex many-body systems ranging from subnuclear to cosmological scales by introducing macroscopic quantities such as particle densities and fluid velocities. According to textbook knowledge, it requires coarse graining over microscopic constituents to define a macroscopic fluid cell, which is large compared to…
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Hydrodynamics provides a successful framework to effectively describe the dynamics of complex many-body systems ranging from subnuclear to cosmological scales by introducing macroscopic quantities such as particle densities and fluid velocities. According to textbook knowledge, it requires coarse graining over microscopic constituents to define a macroscopic fluid cell, which is large compared to the interparticle spacing and the mean free path. In addition, the entire system must consist of many such fluid cells. In high energy heavy ion collisions, hydrodynamic behaviour is inferred from the observation of elliptic flow. Here, we demonstrate the emergence of elliptic flow in a system of few strongly interacting atoms. In our system a hydrodynamic description is a priori not applicable, as all relevant length scales, i.e. the system size, the inter-particle spacing, and the mean free path are comparable. The single particle resolution, deterministic control over particle number and interaction strength in our experiment allow us to explore the boundaries between a microscopic description and a hydrodynamic framework in unprecedented detail.
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Submitted 3 July, 2025; v1 submitted 18 August, 2023;
originally announced August 2023.
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Observation of Cooper Pairs in a Mesoscopic 2D Fermi Gas
Authors:
Marvin Holten,
Luca Bayha,
Keerthan Subramanian,
Sandra Brandstetter,
Carl Heintze,
Philipp Lunt,
Philipp M. Preiss,
Selim Jochim
Abstract:
Pairing is the fundamental requirement for fermionic superfluidity and superconductivity. To understand the mechanism behind pair formation is an ongoing challenge in the study of many strongly correlated fermionic systems. Cooper pairs are the key ingredient to BCS theory as the microscopic explanation of conventional superconductivity. They form between particles of opposite spin and momentum at…
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Pairing is the fundamental requirement for fermionic superfluidity and superconductivity. To understand the mechanism behind pair formation is an ongoing challenge in the study of many strongly correlated fermionic systems. Cooper pairs are the key ingredient to BCS theory as the microscopic explanation of conventional superconductivity. They form between particles of opposite spin and momentum at the Fermi surface of the system. Here, we directly observe Cooper pairs in a mesoscopic two-dimensional Fermi gas. We apply an imaging scheme that enables us to extract the full in-situ momentum distribution of a strongly interacting Fermi gas with single particle and spin resolution. Our ultracold gas allows us to freely tune between a completely non-interacting, unpaired system and weak attractions, where we find Cooper pair correlations at the Fermi surface. When increasing the attractive interactions even further, the pairs gradually turn into deeply bound molecules breaking up the Fermi surface. Our mesoscopic system is closely related to the physics of nuclei, superconducting grains or quantum dots. With the precise control over interactions, particle number and potential landscape in our experiment, the observables we establish in this work provide a new approach to longstanding questions concerning not only such mesoscopic systems but also their connection to the macroscopic world.
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Submitted 6 June, 2022; v1 submitted 23 September, 2021;
originally announced September 2021.
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Observation of Pauli Crystals
Authors:
Marvin Holten,
Luca Bayha,
Keerthan Subramanian,
Carl Heintze,
Philipp M. Preiss,
Selim Jochim
Abstract:
The Pauli exclusion principle is a fundamental law underpinning the structure of matter. Due to their anti-symmetric wave function, no two fermions can occupy the same quantum state. Here, we report on the direct observation of the Pauli principle in a continuous system of up to six particles in the ground state of a two-dimensional harmonic oscillator. To this end, we sample the full many-body wa…
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The Pauli exclusion principle is a fundamental law underpinning the structure of matter. Due to their anti-symmetric wave function, no two fermions can occupy the same quantum state. Here, we report on the direct observation of the Pauli principle in a continuous system of up to six particles in the ground state of a two-dimensional harmonic oscillator. To this end, we sample the full many-body wavefunction by applying a single atom resolved imaging scheme in momentum space. We find so-called Pauli crystals as a manifestation of higher order correlations. In contrast to true crystalline phases, these unique high-order density correlations emerge even without any interactions present. Our work lays the foundation for future studies of correlations in strongly interacting systems of many fermions.
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Submitted 16 December, 2020; v1 submitted 8 May, 2020;
originally announced May 2020.
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Quantum scale anomaly and spatial coherence in a 2D Fermi superfluid
Authors:
Puneet A. Murthy,
Nicolò Defenu,
Luca Bayha,
Marvin Holten,
Philipp M. Preiss,
Tilman Enss,
Selim Jochim
Abstract:
Quantum anomalies are violations of classical scaling symmetries caused by quantum fluctuations. Although they appear prominently in quantum field theory to regularize divergent physical quantities, their influence on experimental observables is difficult to discern. Here, we discovered a striking manifestation of a quantum anomaly in the momentum-space dynamics of a 2D Fermi superfluid of ultraco…
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Quantum anomalies are violations of classical scaling symmetries caused by quantum fluctuations. Although they appear prominently in quantum field theory to regularize divergent physical quantities, their influence on experimental observables is difficult to discern. Here, we discovered a striking manifestation of a quantum anomaly in the momentum-space dynamics of a 2D Fermi superfluid of ultracold atoms. We measured the position and pair momentum distribution of the superfluid during a breathing mode cycle for different interaction strengths across the BEC-BCS crossover. Whereas the system exhibits self-similar evolution in the weakly interacting BEC and BCS limits, we found a violation in the strongly interacting regime. The signature of scale-invariance breaking is enhanced in the first-order coherence function. In particular, the power-law exponents that characterize long-range phase correlations in the system are modified due to this effect, indicating that the quantum anomaly has a significant influence on the critical properties of 2D superfluids.
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Submitted 12 May, 2018;
originally announced May 2018.
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Anomalous breaking of scale invariance in a two-dimensional Fermi gas
Authors:
Marvin Holten,
Luca Bayha,
Antonia C. Klein,
Puneet A. Murthy,
Philipp M. Preiss,
Selim Jochim
Abstract:
The frequency of the breathing mode of a classical two dimensional Fermi gas in a harmonic confinement is fixed by the scale invariance of the Hamiltonian. Scale invariance is broken on the quantum mechanical level by introducing the two dimensional scattering length as a regulator. This is an example of a quantum anomaly in the field of ultracold atoms and leads to a shift of the frequency of the…
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The frequency of the breathing mode of a classical two dimensional Fermi gas in a harmonic confinement is fixed by the scale invariance of the Hamiltonian. Scale invariance is broken on the quantum mechanical level by introducing the two dimensional scattering length as a regulator. This is an example of a quantum anomaly in the field of ultracold atoms and leads to a shift of the frequency of the collective breathing mode of the cloud. In this work, we study this anomalous frequency shift for a two component Fermi gas in the strongly interacting regime. We measure significant shifts away from the scale invariant result that depend strongly on both interactions and temperature. We find qualitative agreement with theoretical calculations at zero temperature.
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Submitted 31 October, 2018; v1 submitted 23 March, 2018;
originally announced March 2018.