Rxiv mechanobio4d ago
📰 "Effective Faraday interaction between light and Helium-3 nuclear spins in a multi-pass cell"
https://arxiv.org/abs/2606.20328 #Physics.Atom-Ph #Pressure #Quant-Ph #Cell
Effective Faraday interaction between light and Helium-3 nuclear spins in a multi-pass cell

Helium-3 nuclear spins form an exceptionally stable quantum system with extremely long coherence time, offering exciting opportunities for quantum technologies. In particular, nuclear spin-squeezed states promise enhanced precision for sensing tasks and tests of new physics. A central challenge for all these applications is the realization of a controllable light-nuclear spin interface. Here we experimentally demonstrate such an interface by exploiting metastability-exchange collisions in a low-pressure helium-3 gas cell at room temperature. A radio-frequency discharge produces a small population of metastable atoms that both enables efficient optical pumping and mediates an effective Faraday interaction between the collective nuclear spin and an optical probe. We quantitatively characterize the strength of this interaction as a function of the nuclear polarization, applied magnetic field, and probe-beam parameters. Moreover, we show that using a multi-pass cell enhances this interaction by effectively increasing the optical depth. Extrapolating to a tenfold increase of the probe power used in the present experiment, we project a measurement-induced squeezing rate of 0.52 s$^{-1}$. Our results provide a practical pathway for optical access to helium-3 nuclear spins and open prospects for generating long-lived, macroscopic nuclear spin-squeezed states for quantum metrology.

arXiv.org
Rxiv mechanobio6d ago
📰 "Tensor network compression using fluid dynamics as a testbed: Analytical foundations in one dimension"
https://arxiv.org/abs/2606.17064 #Physics.Comp-Ph #Physics.Flu-Dyn #Dynamics #Quant-Ph #Matrix
Tensor network compression using fluid dynamics as a testbed: Analytical foundations in one dimension

High performance computers produce extreme-scale data sets that require sampling or compression if they are to be used to their full potential. Existing data compression techniques typically exploit features such as sparsity in the data, homogeneity in the data, or {\it a priori} knowledge of what subsets of data are of most interest. Fluid dynamics data in general do not exhibit these features and so are attractive test beds for generic compression techniques that are objective, robust, and tuneable with respect to information lost due to compression. Presented here is a method based on tensor networks, specifically matrix product states or tensor trains, that meets these requirements. The method is demonstrated for compression in one-dimension and is extensible to higher dimensionality. Lossless compression is demonstrated for random Fourier series for sufficiently high bond dimension of the tensor network, with the memory required to store the tensor network scaling directly proportional to the bond dimension. The lossy compression exhibited at lower bond dimension can be well within the relative error of many fluid simulations. The compression algorithm is tested for the time evolution of Burger's equation with excellent results. We additionally demonstrate the capability to perform computations in the compressed form through a tensor network periodic convolution that can be orders of magnitude faster than using fast Fourier transforms and the convolution theorem. In addition to being an attractive method for working with data sets generated by existing computers, the tensor network methods utilised are directly translatable to the emerging paradigm of quantum computing.

arXiv.org
Rxiv mechanobioJun 15
📰 "Computational regimes in matrix-product-state-based quantum trajectory simulations"
https://arxiv.org/abs/2606.13779 #Physics.Comp-Ph #Dynamics #Quant-Ph #Matrix
Computational regimes in matrix-product-state-based quantum trajectory simulations

Efficient simulation of open quantum systems is central to modeling noisy quantum hardware and many-body dynamics. In trajectory-based tensor network methods, cost is often associated with trajectory-level quantities such as entanglement growth or bond dimension. However, the total cost of a fixed-accuracy simulation also depends on statistical sampling, and the interplay between per-trajectory complexity and sampling effort remains poorly understood. Here we introduce a cost-resolved framework for matrix product state (MPS)-based quantum trajectory simulations that decomposes total cost into memory per trajectory, runtime per trajectory, and sampling effort. We show that physically equivalent stochastic unravelings of the same Lindblad dynamics do not necessarily reduce total cost, but instead redistribute cost between trajectory complexity and statistical convergence. This trade-off is quantified by two dimensionless inflation factors: a bond dimension inflation $α$ and a sampling inflation $κ$, which together determine the preferred unraveling under hardware-dependent memory and parallelism constraints. We provide a practical protocol for extracting $(α,κ)$ from modest pilot simulations and demonstrate it using benchmarks across multiple noise channels. The resulting decision maps show that the computationally favorable unraveling can change with noise strength, time-step resolution, system size, and available parallelism. These results establish unraveling choice as a hardware-aware simulation design problem rather than an intrinsic optimization of trajectory entanglement alone.

arXiv.org
Bart PendersJun 12
Join us as a postdoctoral researcher! "Invisible Knowledge Work in Open Science Practices", funded by OSNL #STS #metascience Come help us map and understand the invisible labour that enables, allows, supports and shapes #openscience, and lets it grow. Mostly #qual work, with small #quant pockets.

Postdoctoral Researcher Invisi...
Postdoctoral Researcher Invisible knowledge work in open science practices

Welcome to Maastricht University! Are you an ambitious post-doctoral researcher with an Open Science mindset who seeks to unravel the threads of visibility and invisibility of staff across research projects? For an Open Science NL funded research project “Inv…

AcademicTransfer
Rxiv mechanobioJun 8
📰 "Cyclic ladder operators and hidden Weyl-Heisenberg structure in a Floquet system"
https://arxiv.org/abs/2606.06810 #Physics.Optics #Dynamics #Quant-Ph #Matrix
Cyclic ladder operators and hidden Weyl-Heisenberg structure in a Floquet system

Ladder operators, found in the quantum harmonic oscillator and other quantized systems, provide an elegant approach to solving or understanding otherwise intricate physics problems. In this Letter, we discuss cyclic ladder operators in both Hermitian and non-Hermitian systems with a finite Hilbert space, with the highest (lowest) level directly descending (ascending) to the lowest (highest) level via a single raising (lowering) operation. We show that an equally spaced energy ladder emerges when these systems have an underlying Weyl-Heisenberg commutation relation, with the cyclic ladder operators and the temporal evolution operator behaving as the generators of the Weyl-Heisenberg group. We further illustrate such a system using a one-dimensional Floquet lattice, where the cyclic ladder operators become diagonal and the temporal evolution simplifies to a permutation matrix after a Floquet period. Our findings reveal a hidden relation between non-trivial dynamics and algebraic principles in Floquet systems, which may exist for other quantum numbers as well besides the energy levels.

arXiv.org
Rxiv mechanobioJun 8
📰 "Complex-gauge control of anomalous Floquet corner responses in a non-Hermitian physical-synthetic photonic lattice"
https://arxiv.org/abs/2606.07038 #Physics.Optics #Dynamics #Quant-Ph #Matrix
Complex-gauge control of anomalous Floquet corner responses in a non-Hermitian physical-synthetic photonic lattice

We propose a non-Hermitian Floquet photonic lattice formed by a physical resonator coordinate and a synthetic frequency coordinate. A two-step modulation protocol realizes a chiral walk in this physical-synthetic plane, with a real synthetic flux controlling loop interference and imaginary gauge fields controlling non-reciprocal envelopes. We show that anomalous corner pairs at quasienergies zero and \(π/T\) exhibit three distinct layers of physics. A non-Bloch higher-order construction predicts whether the \(0/π\) corner pair exists under open boundaries. The imaginary gauge fields select where the right eigenmodes accumulate. The real flux controls the local interference matrix element that determines whether the doubled-period optical response is visible. As a result, the same topological coexistence sector can be bright, skin-dark, or flux-dark in a local optical measurement. We further show that the complex gauge can tune an exceptional point of the two-period corner propagator. At this point the anomalous response keeps its doubled-period sign alternation, but its envelope becomes algebraic because of a Jordan block. These results provide a photonic route to separate topological existence, skin-selected localization, optical visibility, and defective two-period dynamics in a non-Hermitian synthetic dimension.

arXiv.org
Some Bits: Nelson's LinkblogJun 5
Unsloth Gemma 4 QAT: Some deep-in-the-weeds details about boiling down an LLM to a small size you can run on a single desktop computer (or phone)
https://unsloth.ai/docs/models/gemma-4/qat
#unsloth #google #quant #llm #ai #+
Gemma 4 QAT | Unsloth Documentation

Run Google Gemma 4 QAT models locally, including E2B, E4B, 12B, 26B-A4B, and 31B.

Rxiv mechanobioJun 4
📰 "Polalrized reservoirs in dynamics of polariton condensation"
https://arxiv.org/abs/2606.04808 #Physics.Optics #Quant-Ph #Dynamics #Matrix
Polalrized reservoirs in dynamics of polariton condensation

We review the problem of description of the dynamics of driven-disspipative spinor polariton condensates, focusing on the terms corresponding to the coupling between a macroscopic wavefunction of the condensdate and incoherent excitonic reservoir created by a non-resonant pump. We demonstrate that the existing version of the theory breaks down in case, when reservoir has non-zero components of the Stokes vector corresponding to in-plane linear polarization. The polarization invariant theory of reservoir to condensate coupling is formulated with use of the spin density matrix formalism.

arXiv.org
Show thread𝕂𝚞𝚋𝚒𝚔ℙ𝚒𝚡𝚎𝚕Jun 3

🧵 …langsam, ja langsam, kommt der EU in den Sinn Google & Co in Frage zu stellen. Ich und viele andere "Nerds" schon vor über 3½ Jahern (siehe oben).

«Digitale Souveränität — EU-Parlament verabschiedet sich von Google als Standard-Suchmaschine:
Stattdessen soll das europäische Qwant zum Einsatz kommen. Parallel dazu treibt die KI-Flut auch der Google-Alternative DuckDuckGo immer mehr User zu»

🕵️ https://www.derstandard.at/story/3000000323303/eu-parlament-verabschiedet-sich-von-google-als-standard-suchmaschine

#suchmaschine #euparlament #digital #quant #duckduckgo #ai #ki #suveranitet

EU-Parlament verabschiedet sich von Google als Standard-Suchmaschine

Stattdessen soll das europäische Qwant zum Einsatz kommen. Parallel dazu treibt die KI-Flut auch der Google-Alternative DuckDuckGo immer mehr User zu

DER STANDARD
Rxiv mechanobioJun 1
📰 "Preventing the Breakdown of Tight-Binding Waveguide Optics by L\"owdin Orthogonalization"
https://arxiv.org/abs/2605.31074 #Physics.Optics #Dynamics #Quant-Ph #Matrix
Preventing the Breakdown of Tight-Binding Waveguide Optics by Löwdin Orthogonalization

Many advancements in optics have relied on the tight-binding approximation, which simplifies the description and prediction of complex system behaviors. This approximation describes the dynamics of the total light field by examining the coupling between the guided modes of individual single-mode substructures -- also known as coupled mode theory. However, the underlying assumption, that the guided modes of individual waveguides form an orthogonal basis, breaks down when waveguides are brought into close proximity or when larger arrays are considered. In this work, we systematically analyze the consequences of this non-orthogonality and show that it leads to a generalized eigenvalue problem involving an overlap matrix, causing a fundamental mismatch between the standard TB model and solutions of the paraxial wave equation. To resolve this issue, we introduce a modified TB framework based on the Löwdin orthogonalization, which constructs an orthonormal basis from the non-orthogonal guided modes while minimally altering their physical shape and preserving their symmetry properties. The resulting Löwdin-TB method restores the standard eigenvalue problem and yields excellent agreement with exact beam propagation simulations across a wide range of system sizes and waveguide separations. Furthermore, it captures important physical effects, such as enhanced long-range coupling and nontrivial hopping phases, that are absent in the standard approach.

arXiv.org