arXiv subjects

Robin Löwenberg

Publications and source records attributed to Robin Löwenberg.

4 recordsLinked to original sources

arXiv2026

Matrix Holography on an Optical Lattice

We propose an analog quantum-simulation protocol based on a lattice of atomic ensembles and time-averaged Floquet dynamics to construct the four-body potentials that typically appear in bosonic BFSS-like matrix quantum mechanics. In contrast to gate-based digital implementations requiring deep circuits, our approach generates the target model through a fixed set of control stages per Floquet cycle, keeping the number of consecutive unitaries constant with respect to the matrix size $N$. The principal scaling cost in our construction is given by the frequency range required to control the growing lattice. We show that this cost grows at most as $\mathcal{O}(N^3)$, giving a polynomial scaling route to large$-N$, attractive to experimental implementation. Additionally, we demonstrate that the coupling parameter can be tuned beyond $\mathcal{O}(1)$, enabling the simulation of strong-coupling physics necessary for holographic phases.

hep-th↗

arXiv2026

Measuring Rényi entropy with an Echo Protocol

We present efficient and practical protocols to measure the second Rényi entropy, whose exponential is known as the purity. Our approach is based on expressing the purity in terms of transition probabilities generated by an echo-type forward-backward evolution sequence, making it applicable to quantum many-body systems. Notably, our approach does not rely on random-noise averaging, a feature that can be extended to protocols to measure out-of-time-order correlation functions, as we demonstrate. By way of example, we show that our protocols can be practically implemented in superconducting qubit-based platforms, as well as in cavity-QED trapped ultra-cold gases.

quant-ph↗

arXiv2026

Realizing Unitary $k$-designs with a Single Quench

We present a single-quench protocol that generates unitary $k$-designs with minimal control. A system first evolves under a random Hamiltonian $H_1$; at a switch time $t_s \geq t_{\mathrm{Th}}$ (the Thouless time), it is quenched to an independently drawn $H_2$ from the same ensemble and then evolves under $H_2$. This single quench breaks residual spectral correlations that prevent strictly time-independent chaotic dynamics from forming higher-order designs. The resulting ensemble approaches a unitary $k$-design using only a single control operation -- far simpler than Brownian schemes with continuously randomized couplings or protocols that apply random quenches at short time intervals. Beyond offering a direct route to Haar-like randomness, the protocol yields an operational, measurement-friendly definition of $t_{\mathrm{Th}}$ and provides a quantitative diagnostic of chaoticity. It further enables symmetry-resolved and open-system extensions, circuit-level single-quench analogs, and immediate applications to randomized measurements, benchmarking, and tomography.

quant-ph↗

arXiv2023

Lorentz Force Detuning in Heterodyne Gravitational Wave Experiments

Heterodyne cavity experiments for gravitational wave (GW) detection experience a rising interest since recent studies showed that they allow to probe the ultra high frequency regime above $10\,\text{kHz}$. In this paper, we present a concise theoretical study of the experiment based on ideas from the former MAGO collaboration which already started experiments in turn of the millenium. It extends the former results via deriving an additional term originating from a back-action of the electromagnetic field on the cavity walls, also known as Lorentz Force Detuning. We argue that this term leads to a complex dependence of the signal power $P_{\text{sig}}$ on the coupling coefficient between the mechanical shell modes and the electromagnetic eigenmodes of the cavity. It turns out that one has to adapt the coupling over the whole parameter space since the optimal value depends on the mechanical mode $ω_l$ and the GW frequency $ω_g$. This result is particularly relevant for the design of future experiments.

gr-qc↗