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#quant

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Rxiv mechanobio

📰 "Divisible and indivisible Stochastic-Quantum dynamics"
arxiv.org/abs/2505.08785 #Physics.Data-An #Quant-Ph #Dynamics #Matrix

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arXiv.orgDivisible and indivisible Stochastic-Quantum dynamicsThis work presents a complete geometrical characterisation of divisible and indivisible time-evolution at the level of probabilities for systems with two configurations, open or closed. Our new geometrical construction in the space of stochastic matrices shows the existence of conical bounds separating divisible and indivisible dynamics, bearing analogy with the relativistic causal structure, with an emerging time pointing towards information erasure when the dynamics are divisible. Indivisible dynamics, which include quantum dynamics, are characterised by a time-flow against the information-erasure time coordinate or by being tachyonic with respect to the cones in the stochastic matrix space. This provides a geometric counterpart of other results in the literature, such as the equivalence between information-decreasing and divisible processes. The results apply under minimal assumptions: (i) the system has two configurations, (ii) one can freely ascribe initial probabilities to both and (iii) probabilities at other times are linearly related to the initial ones through conditional probabilities. The optional assumption of (iv) continuity places further constraints on the system, removing one of the past cones. Discontinuous stochastic dynamics in continuous time include cases with divisible blocks of evolution which are not themselves divisible. We show that the connection between continuity and multiplicity of divisors holds for any dimension. We extend methods of coarse graining and dilations by incorporating dynamics and uncertainty, connecting them with divisibility criteria. This is a first step towards a full geometric characterisation of indivisible stochastic dynamics for any number of configurations which, as they cannot at the level of probabilities be reduced to a composition of evolution operators, constitute fundamental elements of probabilistic time-evolution.
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Thierry Van Kerm

@pixelsfr il est temps que l'Europe ou les entreprises européennes proposent des solutions aux technologies étasuniennes. Que vivent et se développent des initiatives comme #framasoft #quant ou #vivaldi !
A quand un substitut à Android et Apple pour les téléphones?
Et, l'Europe a développé un système plus performant pour la géolocalisation, à quand le remplacement de Google Map?

Trump tait l'hégémonie technologique étasunienne dans ces délires et calculs. Il est temps de s'en libérer.

Public
Rxiv mechanobio

📰 "Emergence of a Classical Dirac-Type Spin from On-Shell Factorisation and Liouvillian Evolution"
arxiv.org/abs/2505.03551 #Physics.Class-Ph #Mechanics #Quant-Ph #Matrix

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arXiv.orgEmergence of a Classical Dirac-Type Spin from On-Shell Factorisation and Liouvillian EvolutionWhile Liouville's theorem is first order in time for the phase-space distribution itself, the relativistic mass-shell constraint $p^μp_μ= m^2$ is naively second order in energy. We argue it is reasonable to unify both energy branches within a single Hamiltonian by factorising $(p^2 - m^2)$ in analogy with Dirac's approach in relativistic quantum mechanics. We show the resulting matrix-based Liouville equation remains first order and naturally yields a $4\times4$ matrix-valued probability density function in phase space as a classical analogue of a relativistic spin-half Wigner function.
Public
Rxiv mechanobio

📰 "QCMaquis 4.0: Multi-Purpose Electronic, Vibrational, and Vibronic Structure and Dynamics Calculations with the Density Matrix Renormalization Group"
arxiv.org/abs/2505.01405 #Physics.Comp-Ph #Physics.Chem-Ph #Cond-Mat.Str-El #Quant-Ph #Dynamics #Matrix

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arXiv.orgQCMaquis 4.0: Multi-Purpose Electronic, Vibrational, and Vibronic Structure and Dynamics Calculations with the Density Matrix Renormalization GroupQCMaquis is a quantum chemistry software package for general molecular structure calculations in a matrix product state/matrix product operator formalism of the density matrix renormalization group (DMRG). It supports a wide range of features for electronic structure, multi-component (pre-Born-Oppenheimer), anharmonic vibrational structure, and vibronic calculations. In addition to the ground and excited state solvers, QCMaquis allows for time propagation of matrix product states based on the tangent-space formulation of time-dependent DMRG. The latest developments include transcorrelated electronic structure calculations, very recent vibrational and vibronic models, and a convenient Python wrapper, facilitating the interface with external libraries. This paper reviews all the new features of QCMaquis and demonstrates them with new results.
Public
Rxiv mechanobio

📰 "Statistical noise enhances quantumness benefits in spin-network quantum reservoir computing"
arxiv.org/abs/2504.17837 #Physics.Comp-Ph #Dynamics #Quant-Ph #Matrix

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arXiv.orgStatistical noise enhances quantumness benefits in spin-network quantum reservoir computingQuantum reservoir computing offers a promising approach to the utilization of complex quantum dynamics in machine learning. Statistical noise inevitably arises in real settings of quantum reservoir computing (QRC) due to the practical necessity of taking a small to moderate number of measurements. We investigate the effect of statistical noise in spin-network QRC on the possible performance benefits conferred by quantumness. As our measures of quantumness, we employ both quantum entanglement, which we quantify by the partial transpose of the density matrix, and coherence, which we quantify as the sum of the absolute values of the off-diagonal elements of the density matrix. We find that reservoirs which enjoy a finite degree of quantum entanglement and coherence are more stable against the adverse effects of statistical noise on performance compared to their unentangled, incoherent counterparts. Our results indicate that the potential benefit reservoir computers may derive from quantumness depends on the number of measurements used for training and testing, and may indeed be enhanced by statistical noise. These findings not only emphasize the importance of incorporating realistic noise models, but also suggest that the search for quantum advantage may be aided rather than impeded by the practical constraints of implementation within existing machines.
Public
Rxiv mechanobio

📰 "Simulating quantum dynamics in two-dimensional lattices with tensor network influence functional belief propagation"
arxiv.org/abs/2504.07344 #Cond-Mat.Str-El #Physics.Comp-Ph #Quant-Ph #Dynamics #Matrix

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arXiv.orgSimulating quantum dynamics in two-dimensional lattices with tensor network influence functional belief propagationDescribing nonequilibrium quantum dynamics remains a significant computational challenge due to the growth of spatial entanglement. The tensor network influence functional (TN-IF) approach mitigates this problem for computing the time evolution of local observables by encoding the subsystem's influence functional path integral as a matrix product state (MPS), thereby shifting the resource governing computational cost from spatial entanglement to temporal entanglement. We extend the applicability of the TN-IF method to two-dimensional lattices by demonstrating its construction on tree lattices and proposing a belief propagation (BP) algorithm for the TN-IF, termed influence functional BP (IF-BP), to simulate local observable dynamics on arbitrary graphs. Even though the BP algorithm introduces uncontrolled approximation errors on arbitrary graphs, it provides an accurate description for locally tree-like lattices. Numerical simulations of the kicked Ising model on a heavy-hex lattice, motivated by a recent quantum experiment, highlight the effectiveness of the IF-BP method, which demonstrates superior performance in capturing long-time dynamics where traditional tensor network state-based methods struggle. Our results further reveal that the temporal entanglement entropy (TEE) only grows logarithmically with time for this model, resulting in a polynomial computational cost for the whole method. We further construct a cluster expansion of IF-BP to introduce loop correlations beyond the BP approximation, providing a systematic correction to the IF-BP estimate. We demonstrate the power of the cluster expansion of the IF-BP in simulating the quantum quench dynamics of the 2D transverse field Ising model, obtaining numerical results that improve on the state-of-the-art.
Public
Rxiv mechanobio

📰 "Quantum Discrete Variable Representations"
arxiv.org/abs/2504.15841 #Physics.Comp-Ph #Physics.Chem-Ph #Mechanical #Quant-Ph #Matrix

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arXiv.orgQuantum Discrete Variable RepresentationsWe present a fault-tolerant quantum algorithm for implementing the Discrete Variable Representation (DVR) transformation, a technique widely used in simulations of quantum-mechanical Hamiltonians. DVR provides a diagonal representation of local operators and enables sparse Hamiltonian structures, making it a powerful alternative to the finite basis representation (FBR), particularly in high-dimensional problems. While DVR has been extensively used in classical simulations, its quantum implementation, particularly using Gaussian quadrature grids, remains underexplored. We develop a quantum circuit that efficiently transforms FBR into DVR by following a recursive construction based on quantum arithmetic operations, and we compare this approach with methods that directly load DVR matrix elements using quantum read-only memory (QROM). We analyze the quantum resources, including T-gate and qubit counts, required for implementing the DVR unitary and discuss preferable choices of QROM-based and recursive-based methods for a given matrix size and precision. This study lays the groundwork for utilizing DVR Hamiltonians in quantum algorithms such as quantum phase estimation with block encoding.
Public
Rxiv mechanobio

📰 "Lyapunov Dynamics in Entangled Biphoton Spectroscopy"
arxiv.org/abs/2504.14086 #Physics.Chem-Ph #Physics.Optics #Dynamics #Quant-Ph #Matrix

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arXiv.orgLyapunov Dynamics in Entangled Biphoton SpectroscopyRecent advances in quantum light spectroscopy highlight the potential of using entangled photons as a sensitive probe for many-body dynamics and material correlations. However, a comprehensive theory to explain experimental results remains elusive, primarily due to the complexity of the Hilbert space and the intricate interactions and nonlinearities inherent in material systems. In this work, we introduce a tractable model based on a finite-sized correlation matrix governed by a bilinear bosonic Hamiltonian, enabling efficient simulations through Gaussian-preserving dynamics. We apply this framework to compute the output joint spectral intensity (JSI) and von Neumann entropy of frequency-entangled biphotons, and find close agreement with experimental observations in empty microcavities. Our results reveal the emergence of off-diagonal spectral correlations that can be interpreted as irreversible decay of cavity excitations into the biphoton continua. This approach offers a powerful theoretical tool for interpreting quantum spectroscopic data and paves the way for probing more complex light-matter interactions in materials.
Public
Rxiv mechanobio

📰 "Geometric Learning Dynamics"
arxiv.org/abs/2504.14728 #Dynamics #Quant-Ph #Q-Bio.Pe #Matrix #Cs.Lg

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arXiv.orgGeometric Learning DynamicsWe present a unified geometric framework for modeling learning dynamics in physical, biological, and machine learning systems. The theory reveals three fundamental regimes, each emerging from the power-law relationship $g \propto κ^a$ between the metric tensor $g$ in the space of trainable variables and the noise covariance matrix $κ$. The quantum regime corresponds to $a = 1$ and describes Schrödinger-like dynamics that emerges from a discrete shift symmetry. The efficient learning regime corresponds to $a = \tfrac{1}{2}$ and describes very fast machine learning algorithms. The equilibration regime corresponds to $a = 0$ and describes classical models of biological evolution. We argue that the emergence of the intermediate regime $a = \tfrac{1}{2}$ is a key mechanism underlying the emergence of biological complexity.
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AndyGER :verified_coffee:

Uff!

Ich habe #apple #safari gerade die europäische Suchmaschine #quant beigebracht und leicht war das nicht! Also nicht trivial. Ein Einsteiger könnte daran verzweifeln. Das muss einfacher gehen, Apple.

Überhaupt ist die Zahl an Erweiterungen für Safari weiterhin sehr bescheiden. Zwar liefert der Browser eine Menge Tools mit, aber da ginge sicher noch mehr. (1/2)

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David Palk#RejoinEU 💖🇪🇺🤎🕊

@Ruth_Mottram #vivaldi seems pretty tight, if I can break something I will. As for #linux & #quant I'm still waiting on the #USB boot . They sent me 5 install disks, how very quaint and totally useless as I've no readers/burners on any of my kit. Their download / install from the #web don't work either. Go figure! Tempted to write my own but haven't ten years to waste. Now 70+ was writing code in the early 70's, lol.

Public
Viktoria D. Richards/Uddelhexe

Was mir grad krass auffällt, wo ich eine Fotoreferenz für eine Zeichnung suche:

Ich verwende ja mittlerweile #Quant oder ansonsten DuckduckGo als Suchmaschine.
Da die aber natürlich nicht so gefüttert und KI geboostet sind (was auch gut so ist) wie Google, find ich manchmal zu einem Suchbegriff echt nix und wechsle grummelnd zu #Google.

Alter, ist deren Bildergebnissliste voll mit bescheuerten #KI Vorschaubildern! Das ist ja nicht zum Aushalten!

Da geh ich lieber selbst n Foto machen...Alter

Public
Rxiv mechanobio

📰 "The Birth of Quantum Mechanics: A Historical Study Through the Canonical Papers"
arxiv.org/abs/2503.13630 #Physics.Hist-Ph #Mechanics #Quant-Ph #Matrix

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arXiv.orgThe Birth of Quantum Mechanics: A Historical Study Through the Canonical PapersThis paper explores the historical development of the theory of quantum mechanics between 1900 and 1927 by chronological examination of the foundational papers and ideas. Beginning with Planck's introduction of energy quantisation in blackbody radiation, we follow the emergence of Einstein's light quanta hypothesis, Bohr's atomic model, and the statistical implications of indistinguishable particles. Special emphasis is placed on the transition from the Old Quantum Theory to modern quantum mechanics, particularly through Heisenberg's matrix mechanics and Schrödinger's wave mechanics. This study aims to provide a structured historical account, offering insights into the conceptual transformations that led to quantum mechanics while making the development accessible to physicists, historians of science, and advanced students interested in the origins of modern quantum theory.
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