arXiv subjects

Gerhard Birkl

Publications and source records attributed to Gerhard Birkl.

At least 19 recordsLinked to original sources

arXiv2026

Efficient Assembly of a Defect-Free Quantum Register of 1024 Neutral-Atom Qubits

Low-entropy arrays of atomic quantum systems in optical tweezers offer unique prospects for fundamental research on few- and many-body systems as well as for extended applications in quantum technology. The significance of this approach relies on the achievable system size, its uniformity, and the rate of qubit allocation. We propel the neutral-atom quantum-technology platform by the rapid assembly of a regular two-dimensional quantum register of up to 1024 atomic qubits, enabled by a novel implementation of intensity-homogenized tweezer arrays and parallelized atom transport. Our highly efficient microoptical architecture modularizes intensity equalization and tweezer patterning in separate functional units, eliminating restrictions that arise for high-power, high-resolution, and large-scale light-field control within a single device. Arrays of precise grid structure, trap depth, and vibrational frequency with more than 3500 sites are demonstrated. Individual sites are interconnected by up to 50 parallelized transport tweezers with intensity and position control in real-time for swift qubit relocation. Multi-tweezer transport enables the operation of target patterns of up to 32 x 32 sites with sustained near-unity filling fraction. These results boost neutral-atom quantum information science above the kiloqubit level.

quant-ph↗

arXiv2026

Josephson spectroscopy in a circular atomic tunnel junction with acceleration-induced symmetry breaking

We study Josephson dynamics in a long atomic Bose-Josephson junction formed by two tunnel-coupled coplanar Bose-Einstein-condensate rings. An in-plane linear acceleration breaks the axial symmetry of the trap and transforms a single Josephson plasma oscillation into a multimode population-imbalance response. Gross-Pitaevskii simulations and Bogoliubov-de Gennes analysis show that the additional spectral components arise from collective modes that acquire finite overlap with the population-imbalance operator under symmetry breaking, with their activation governed by reflection symmetry about the acceleration direction. We also propose a mode-resolved Josephson-spectroscopy protocol based on a weak localized periodic perturbation. Frequency scans reveal resonant amplitude peaks and phase shifts at the eigenfrequencies of active Bogoliubov modes, while angular scans of the drive position provide access to the angular structure of the corresponding mode density perturbations. A dissipative time-dependent Bogoliubov theory yields analytical response functions in quantitative agreement with full Gross-Pitaevskii simulations in the linear regime. Our results demonstrate that accelerated dual-ring condensates provide a controllable platform for symmetry-selected Josephson dynamics and spectroscopic probing of collective modes.

cond-mat.quant-gas↗

arXiv2026

Dynamics of repeated BEC formation and extraction in dimple traps

We investigate repeated Bose-Einstein-condensate (BEC) formation and extraction in a dimple trap embedded in a reservoir of thermal atoms using a kinetic model. The model includes pulsed extraction, evaporation, three-body losses, and thermal-atom replenishment. Three extraction protocols are compared: extraction of all atoms from the dimple (BEC and thermal atoms), full and partial extractions of the BEC, but not of the thermal atoms. Residual atoms in the dimple after extraction seed subsequent Bose-stimulated growth and reduce the recovery time between extractions, but also enhance density-dependent losses. For all protocols, repeated extraction of BECs can be achieved without replenishment, but the number of BEC formations is limited by reservoir depletion and heating. With continuous replenishment, the system can reach a periodic steady-state regime, after an initial transient period, controlled by the externally imposed rates of extraction pulses and thermal-atom input. Within the explored parameter range, partial BEC extraction gives the highest efficiency, particularly for short extraction periods and high input rates. These results identify seeding by residual populations of BECs and thermal atoms as a kinetic mechanism for improving repeated condensate production in dimple traps.

cond-mat.quant-gas↗

arXiv2026

Parameter Estimation from Amplitude Collapse in Correlated Matter-Wave Interference

Operating matter-wave interferometers as quantum detectors for fundamental physics or inertial sensors with unprecedented accuracies relies on noise rejection, often implemented by correlating multiple sensors. They can be spatially separated (gradiometry or gravitational-wave detection) or consist of different internal states (magnetometry or quantum clock interferometry), with a signal-amplitude modulation serving as a signature of a differential phase. In this work, we introduce Parameter Estimation from Amplitude Collapse (PEAC) by applying statistical inference techniques for different magnetically sensitive substates of an atom interferometer. We demonstrate that PEAC provides higher trueness, resulting in a substantially reduced bias compared to standard methods for perfectly correlated signals, while achieving competitive precision near, but not at, vanishing amplitudes. This indicates that vanishing signals do not constitute the most favourable working point for high-accuracy sensing, relevant to quantum clock interferometry. PEAC presents a generally applicable complementary evaluation method for correlated interferometers without phase stability, increasing the overall accuracy and enabling applications beyond atom-based interferometry.

quant-ph↗

arXiv2025

Model-Based Real-Time Synthesis of Acousto-Optically Generated Laser-Beam Patterns and Tweezer Arrays

Acousto-optic deflectors (AOD) enable spatiotemporal control of laser beams through diffraction at an ultrasonic grating that is controllable by radio-frequency (rf) waveforms. These devices are a widely used tool for high-bandwidth random-access scanning applications, such as optical tweezers in quantum technology. A single AOD can generate multiple optical tweezers by multitone rf input in one dimension. Two-dimensional (2D) patterns can be realized with two perpendicularly oriented AODs. As the acousto-optical response depends nonlinearly on the applied frequency components, phases, and amplitudes, and in addition experiences dimensional coupling in 2D setups, intensity regulation becomes a unique challenge. Guided by coupled-wave theory and experimental observations, we derive a compute-efficient model which we implement on a graphics processing unit. Only one-time sampling of single-tone laser-power calibration is needed for model parameter determination, allowing for straight-forward integration into optical instruments. We implement and experimentally validate an open-loop diffraction efficiency control system that enables programmable 2D multibeam trajectories with intensity control applied at every time step during digital signal generation, overcoming the limited flexibility, pattern-size constraints, and bandwidth limitations of methods using precalculation and precalibration of a predefined pattern set or closed-loop feedback. The system is capable of stable real-time waveform streaming of arrays with up to 50 x 50 tweezers with minimal time resolution of 1.4 ns (700 MS/s) and a peak latency below 257 microseconds for execution of newly requested patterns. Reactive, real-time 2D multibeam laser patterning and scanning with strict intensity matching will substantially benefit parallelization and increasing data rates in materials processing, microscopy, and optical tweezers.

physics.optics↗

arXiv2025

Rydberg atoms for electric field gradiometry

We propose a quantum sensor for electric fields based on networks of Rydberg atoms. The sensing mechanism exploits the strong dependence of the Rydberg blockade on the applied electric field near a F\"orster resonance. In this regime, variations of the electric field across the array lead to local changes in the blockade radius. Therefore, owing to its spatially distributed architecture, the device can operate as a gradiometer. Our analysis shows that our scheme enables detection of spatial variations in the electric field with a resolution of a few $\mu$m. We analyse the dynamics of Rydberg excitations for systems with different spatial geometries and electric field configurations to establish the relation between the applied field and the blockade response. For spatially inhomogeneous fields, we also provide another observable, density-density correlations, that can probe the field's spatial structure.

quant-ph↗

arXiv2024

Acceleration-driven dynamics of Josephson vortices in coplanar superfluid rings

Precise control of topologically protected excitations, such as quantum vortices in atomtronic circuits, opens new possibilities for future quantum technologies. We theoretically investigate the dynamics of Josephson vortices (rotational fluxons) induced by coupled persistent currents in a system of coplanar double-ring atomic Bose-Einstein condensates. We study the Josephson effect in an atomic Josephson junction formed by coaxial ring-shaped condensates. Tunneling superflows, initiated by an imbalance in atomic populations between the rings, are significantly influenced by the persistent currents in the inner and outer rings. This results in pronounced Josephson oscillations in the population imbalance for both co-rotating and non-rotating states. If a linear acceleration is applied to the system, our analysis reveals peculiar azimuthal tunneling patterns and dynamics of Josephson vortices which leads to non-zero net tunneling current and shows sensitivity to the acceleration magnitude. When multiple Josephson vortices are present, asymmetric vortex displacements that correlate with both the magnitude and direction of acceleration can be measured, offering potential for quantum sensing applications.

cond-mat.quant-gas↗

arXiv2024

Dichroic mirror pulses for optimized higher-order atomic Bragg diffraction

Increasing the sensitivity of light-pulse atom interferometers progressively relies on large-momentum transfer techniques. Precise control of such methods is imperative to exploit the full capabilities of these quantum sensors. One key element is the mitigation of deleterious effects such as parasitic paths deteriorating the interferometric signal. In this Letter, we present the experimental realization of dichroic mirror pulses for atom interferometry, its scalability to higher-order Bragg diffraction, and its robustness against initial momentum spread. Our approach selectively reflects resonant atom paths into the detected interferometer output, ensuring that these contribute to the signal with intent. Simultaneously, parasitic paths are efficiently transmitted by the mirror and not directed to the relevant interferometer outputs. This method effectively isolates the desired interferometric signal from noise induced by unwanted paths. It can be readily applied to existing setups capable of higher-order Bragg diffraction.

quant-ph↗

arXiv2024

Quantum Sensing in Tweezer Arrays: Optical Magnetometry on an Individual-Atom Sensor Grid

We implement a scalable platform for quantum sensing comprising hundreds of sites capable of holding individual laser-cooled atoms and demonstrate the applicability of this single-quantum-system sensor array to magnetic-field mapping on a two-dimensional grid. With each atom being confined in an optical tweezer within an area of 0.5 micrometer^2 at mutual separations of 7.0(2) micrometer, we obtain micrometer-scale spatial resolution and highly parallelized operation. An additional steerable optical tweezer allows for a rearrangement of atoms within the grid and enables single-atom scanning microscopy with sub-micron resolution. This individual-atom sensor platform finds its immediate application in mapping an externally applied DC gradient magnetic field. In a Ramsey-type measurement, we obtain a field resolution of 98(29) nanotesla. We estimate the sensitivity to 25 microtesla/Hz^1/2.

quant-ph↗

arXiv2024

Supercharged two-dimensional tweezer array with more than 1000 atomic qubits

We report on the realization of a large-scale quantum-processing architecture surpassing the tier of 1000 atomic qubits. By tiling multiple microlens-generated tweezer arrays, each operated by an independent laser source, we can eliminate laser-power limitations in the number of allocatable qubits. Already with two separate arrays, we implement combined 2D configurations of 3000 qubit sites with a mean number of 1167(46) single-atom quantum systems. The transfer of atoms between the two arrays is achieved with high efficiency. Thus, supercharging one array designated as quantum processing unit with atoms from the secondary array significantly increases the number of qubits and the initial filling fraction. This drastically enlarges attainable qubit cluster sizes and success probabilities allowing us to demonstrate the defect-free assembly of clusters of up to 441 qubits with persistent stabilization at near-unity filling fraction over tens of detection cycles. The presented method substantiates neutral atom quantum information science by facilitating configurable geometries of highly scalable quantum registers with immediate application in Rydberg-state mediated quantum simulation, fault-tolerant universal quantum computation, quantum sensing, and quantum metrology.

quant-ph↗

arXiv2023

Reservoir-based deterministic loading of single-atom tweezer arrays

State-of-the-art individual-atom tweezer platforms have relied on loading schemes based on spatially superimposing the tweezer array with a cloud of cold atoms created beforehand. Together with immanent atom loss, this dramatically limits the data rate, as the application sequence must be alternated with the time-consuming phases of magneto-optical trapping and laser cooling. We introduce a modular scheme built on an additional cold-atom reservoir and an array of buffer traps effectively decoupling cold-atom accumulation and single-atom supply from the quantum-register operation. For this purpose, we connect a microlens-based tweezer array to a cloud of laser-cooled atoms held in an auxiliary large-focus dipole trap by utilizing atom transport and buffer traps for dedicated single-atom supply. We demonstrate deterministic loading of a hexagonal target structure with atoms solely originating from the reservoir trap. The results facilitate increased data rates and unlock a path to continuous operation of individual-atom tweezer arrays in quantum science, making use of discrete functional modules, operated in parallel and spatially separated.

quant-ph↗

arXiv2023

Scalable multilayer architecture of assembled single-atom qubit arrays in a three-dimensional Talbot tweezer lattice

We report on the realization of a novel platform for the creation of large-scale 3D multilayer configurations of planar arrays of individual neutral-atom qubits: a microlens-generated Talbot tweezer lattice that extends 2D tweezer arrays to the third dimension at no additional costs. We demonstrate the trapping and imaging of rubidium atoms in integer and fractional Talbot planes and the assembly of defect-free atom arrays in different layers. The Talbot self-imaging effect for microlens arrays constitutes a structurally robust and wavelength-universal method for the realization of 3D atom arrays with beneficial scaling properties. With more than 750 qubit sites per 2D layer, these scaling properties imply that 10000 qubit sites are already accessible in 3D in our current implementation. The trap topology and functionality are configurable in the micrometer regime. We use this to generate interleaved lattices with dynamic position control and parallelized sublattice addressing of spin states for immediate application in quantum science and technology.

quant-ph↗

arXiv2023

Defect-free assembly of 2D clusters of more than 100 single-atom quantum systems

We demonstrate the defect-free assembly of versatile target patterns of up 111 neutral atoms, building on a 361-site subset of a micro-optical architecture that readily provides thousands of sites for single-atom quantum systems. By performing multiple assembly cycles in rapid succession, we drastically increase achievable structure sizes and success probabilities. We implement repeated target pattern reconstruction after atom loss and deterministic transport of partial atom clusters necessary for distributing entanglement in large-scale systems. This technique will propel assembled-atom architectures beyond the threshold of quantum advantage and into a regime with abundant applications in quantum sensing and metrology, Rydberg-state mediated quantum simulation, and error-corrected quantum computation.

quant-ph↗

arXiv2022

Coherent dynamics in a five-level atomic system

The coherent control of multi-partite quantum systems presents one of the central prerequisites in state-of-the-art quantum information processing. With the added benefit of inherent high-fidelity detection capability, atomic quantum systems in high-energy internal states, such as metastable noble gas atoms, promote themselves as ideal candidates for advancing quantum science in fundamental aspects and technological applications. Using laser-cooled neon atoms in the metastable $^3$P$_2$ state of state $1s^2 2s^2 2p^5 3s$ (LS-coupling notation) (Racah notation: $^2P_{3/2}\,3s[3/2]_2$) with five $m_F$-sublevels, experimental methods for the preparation of all Zeeman sublevels |m_J> = |+2>, |+1>, |0>, |-1>, |-2> as well as the coherent control of superposition states in the five-level system |+2> ... |-2>, in the three-level system |+2>, |+1>, |0>, and in the two-level system |+2>, |+1> are presented. The methods are based on optimized radio frequency and laser pulse sequences. The state evolution is described with a simple, semiclassical model. The coherence properties of the prepared states are studied using Ramsey and spin echo measurements.

quant-ph↗

arXiv2022

Generation of Josephson vortices in stacked toroidal Bose-Einstein condensates

Coupled coaxially stacked toroidal condensates with persistent currents suggest an appealing physical platform for the investigation of various phenomena related to interacting superflows from Josephson effects in the regime of weak interactions to the quantum Kelvin-Helmholtz instability for merging rings. We suggest experimentally accessible methods to prepare states with different topological charges in two coupled coaxial ring-shaped atomic Bose-Einstein condensates. Our results open up the way to direct observation of rotational Josephson vortices in atomic Bose-Einstein condensates.

cond-mat.quant-gas↗

arXiv2022

Wideband current modulation of diode lasers for frequency stabilization

We present a current-modulation technique for diode-laser systems that is specifically designed for high-bandwidth laser-frequency stabilization and wideband frequency modulation with a flat transfer function. It consists of a dedicated current source and an impedance-matching circuit both placed close to the laser diode. The transfer behaviour of the system is analysed under realistic conditions employing an external-cavity diode laser (ECDL) system. We achieve a phase lag less than 90$°$ up to 25 MHz and a gain flatness of $\pm$ 3 dB in the frequency range of DC to 100 MHz while the passive stability of the laser system is not impaired. The potential of the presented current modulation scheme is demonstrated in an optical phase-locked-loop between two ECDL systems resulting in an improved phase noise of 42 mrad$_{rms}$. The design files are available as an open-source project.

physics.optics↗

arXiv2020

Digital laser frequency and intensity stabilization based on the STEMlab platform (originally Red Pitaya)

We report on the development, implementation, and characterization of digital controllers for laser frequency stabilization as well as intensity stabilization and control. Our design is based on the STEMlab (originally Red Pitaya) platform. The presented analog hardware interfaces provide all necessary functionalities for the designated applications and can be integrated in standard 19-inch rack mount units. Printed circuit board layouts are made available as an open-source project.\cite{APQGit_Lockbox,APQGit_IntStab} A detailed characterization shows that the bandwidth 1.25 MHz and the noise performance of the controllers are limited by the STEMlab system and not affected by the supplementary hardware. Frequency stabilization of a diode laser system resulting in a linewidth of 52(1) kHz (FWHM) is demonstrated. Intensity control to the $10^{-3}$ level with sub-microsecond rise and fall times based on an acousto-optic modulator as actuator is achieved.

physics.ins-det↗

arXiv2020

Assembled arrays of Rydberg-interacting atoms

Assembled arrays of individual atoms with Rydberg-mediated interactions provide a powerful platform for the simulation of many-body spin Hamiltonians as well as the implementation of universal gate-based quantum information processing. We demonstrate the first realization of Rydberg excitations and controlled interactions in microlens-generated multisite trap arrays of reconfigurable geometry. We utilize atom-by-atom assembly for the deterministic preparation of pre-defined 2D structures of rubidium Rydberg atoms with exactly known mutual separations and selectable interaction strength. By adapting the geometry and the addressed Rydberg state, a parameter regime spanning from weak interactions to strong coupling can be accessed. We characterize the simultaneous coherent excitation of non-interacting atom clusters for the state $\mathrm{57D_{5/2}}$ and analyze the experimental parameters and limitations. For configurations optimized for Rydberg blockade utilizing the state $\mathrm{87D_{5/2}}$, we observe collectively enhanced Rabi oscillations.

quant-ph↗