Classical Worlds Research Articles

Can Classical Worlds Emerge from Parallel Quantum Universes?

Can Classical Worlds Emerge from Parallel Quantum Universes?

The quantum Gaussian-Schell model: a link between classical and quantum optics.

The quantum theory of the electromagnetic field uncovered that classical forms of light were indeed produced by distinct superpositions of nonclassical multiphoton wave packets. This situation prevails for partially coherent light, the most common kind of classical light. Here, for the first time, to our knowledge, we demonstrate the extraction of the constituent multiphoton quantum systems of a partially coherent light field. We shift from the realm of classical optics to the domain of quantum optics via a quantum representation of partially coherent light using its complex-Gaussian statistical properties. Our formulation of the quantum Gaussian-Schell model (GSM) unveils the possibility of performing photon-number-resolving (PNR) detection to isolate the constituent quantum multiphoton wave packets of a classical light field. We experimentally verified the coherence properties of isolated vacuum systems and wave packets with up to 16 photons. Our findings not only demonstrate the possibility of observing quantum properties of classical macroscopic objects but also establish a fundamental bridge between the classical and quantum worlds.

Perspective on an Emerging Frontier of Nanoscience Opened up by Dressed Photon Studies

The core parts of developing dressed photon (DP) research that require advanced knowledge of highly mathematical quantum field theory and their potentially important impacts on the wide spectrum of long-term scientific activities in general, not necessarily restricted to those in the natural science sector, are succinctly explained in this article. Although a considerable number of remarkable technological achievements in the field of nanophotonics have been attained by utilizing DP phenomena, from the theoretical viewpoint, they remain enigmatic, as in the case of dark matter and energy in cosmology. Under such circumstances, an intriguing working hypothesis (WH) for DPs is proposed by the authors of this article through a combination of Ojima’s micro-macro duality theory and the Greenberg-Robinson theorem, claiming that the space-like momentum contribution is an inevitable element for quantum field interactions to occur. Note that, as the Schrödinger’s cat thought experiment clearly shows, the widespread common quantum mechanics knowledge is incapable of explaining how the invisible quantum world is connected to our familiar visible classical world. In the above-mentioned WH, the main reason why we cannot explain either DPs or dark entities in cosmology is shown to have roots in the fact that the prevailing theories have not revealed an important role of spacelike momentum in connecting the quantum and classical worlds. Our new WH further shows that the entire universe is connected by an instantaneous spacelike entropic spin network, as in the case of quantum spin entanglement explained in mainstream physics. Since such a network may have a close relation with the nonlocal consciousness field, which seems to be the final frontier of physics, our perspective on such a possibility is briefly given in the final section of this paper.

Systematically Constructing Mesoscopic Quantum States Relevant to Periodic Orbits in Integrable Billiards from Directionally Resolved Level Distributions

Two-dimensional quantum billiards are one of the most important paradigms for exploring the connection between quantum and classical worlds. Researchers are mainly focused on nonintegrable and irregular shapes to understand the quantum characteristics of chaotic billiards. The emergence of the scarred modes relevant to unstable periodic orbits (POs) is one intriguing finding in nonintegrable quantum billiards. On the other hand, stable POs are abundant in integrable billiards. The quantum wavefunctions associated with stable POs have been shown to play a key role in ballistic transport. A variety of physical systems, such as microwave cavities, optical fibers, optical resonators, vibrating plates, acoustic waves, and liquid surface waves, are used to analogously simulate the wave properties of quantum billiards. This article gives a comprehensive review for the subtle connection between the quantum level clustering and the classical POs for three integrable billiards including square, equilateral triangle, and circular billiards.

Entangling motional atoms and an optical loop at ambient condition

The observation of quantum entanglement in macroscopic matters has implications in the fundamental studies of quantum mechanics, as well as the implementations of quantum information technologies, such as quantum communication, enhanced sensing, and distributed quantum computing. Here, we report the creation of the heralded entanglement between two different room-temperature quantum memories: a single-photon entangled state delocalized between motional atoms as a collective excitation and an all-optical loop as a flying qubit. The stored entangled state is subsequently retrieved and verified by measuring the nonclassical correlations, quantum interference, and concurrence of the mapped-out photons. Our results show that quantum entanglement can be sustained in macroscopic matters at ambient condition, which enriches the fundamental researches of the transition boundary between quantum and classical worlds. Also, it highlights the potential cooperation between atomic ensembles and all-optical loop as quantum nodes at ambient condition, bringing a significant step towards practical quantum networks.

Innovating for success

AbstractThe presentation of the Quantum Effects Award 2023 will be one of the highlights during Quantum Effects, Trade Fair and Conference for Quantum Technologies, which will be held in Stuttgart on 10 and 11 October 2023. The Award recognizes outstanding innovations that connect the classical and quantum worlds, are used in different industries, enable individual services and open up new perspectives. This also applies to components that significantly advance quantum technologies and solutions.

Schrödinger cat states of a 16-microgram mechanical oscillator

According to quantum mechanics, a physical system can be in any linear superposition of its possible states. Although the validity of this principle is routinely validated for microscopic systems, it is still unclear why we do not observe macroscopic objects to be in superpositions of states that can be distinguished by some classical property. Here we demonstrate the preparation of a mechanical resonator in Schrödinger cat states of motion, where the ∼1017 constituent atoms are in a superposition of two opposite-phase oscillations. We control the size and phase of the superpositions and investigate their decoherence dynamics. Our results offer the possibility of exploring the boundary between the quantum and classical worlds and may find applications in continuous-variable quantum information processing and metrology with mechanical resonators.

FIRST-ORDER RELEVANT REASONERS IN CLASSICAL WORLDS

Abstract Sedlár and Vigiani [18] have developed an approach to propositional epistemic logics wherein (i) an agent’s beliefs are closed under relevant implication and (ii) the agent is located in a classical possible world (i.e., the non-modal fragment is classical). Here I construct first-order extensions of these logics using the non-Tarskian interpretation of the quantifiers introduced by Mares and Goldblatt [12], and later extended to quantified modal relevant logics by Ferenz [6]. Modular soundness and completeness are proved for constant domain semantics, using non-general frames with Mares–Goldblatt truth conditions. I further detail the relation between the demand that classical possible worlds have Tarskian truth conditions and incompleteness results in quantified relevant logics.

QUANTUM THEOLOGY AND “‘WE’ AND ‘THEY’”

QUANTUM THEOLOGY AND “‘WE’ AND ‘THEY’”

THE ENTANGLED TRINITY, QUANTUM BIOLOGY, AND DEEP INCARNATION

AbstractBy utilizing the concept of quantum decoherence, augmented by the novel theory of quantum Darwinism, to understand the transition from the quantum to the classical worlds, the scaling up of the concept of quantum entanglement2018 to the biological level offers a fascinating metaphor for the presence of the creative spirit in nature and the “flesh” of Incarnation. This in turn provides helpful theological metaphors for articulating divine presence at the level of life in theistic evolution, partially addressing the issue of evolutionary theodicy by supporting the concept of deep Incarnation. The point of understanding the Incarnation as deeply entangled enfleshment is that it brings the suffering of creation into the life of the Redeemer as well as the Creator, facilitating redemption and hope through the divine life.

Reliable Optimization of Arbitrary Functions over Quantum Measurements.

As the connection between classical and quantum worlds, quantum measurements play a unique role in the era of quantum information processing. Given an arbitrary function of quantum measurements, how to obtain its optimal value is often considered as a basic yet important problem in various applications. Typical examples include but are not limited to optimizing the likelihood functions in quantum measurement tomography, searching the Bell parameters in Bell-test experiments, and calculating the capacities of quantum channels. In this work, we propose reliable algorithms for optimizing arbitrary functions over the space of quantum measurements by combining the so-called Gilbert's algorithm for convex optimization with certain gradient algorithms. With extensive applications, we demonstrate the efficacy of our algorithms with both convex and nonconvex functions.

Precession-induced nonclassicality of the free induction decay of NV centers by a dynamical polarized nuclear spin bath

The ongoing exploration of the ambiguous boundary between the quantum and the classical worlds has spurred substantial developments in quantum science and technology. Recently, the nonclassicality of dynamical processes has been proposed from a quantum-information-theoretic perspective, in terms of witnessing nonclassical correlations with Hamiltonian ensemble simulations. To acquire insights into the quantum-dynamical mechanism of the process nonclassicality, here we propose to investigate the nonclassicality of the electron spin free-induction-decay process associated with an NV− center. By controlling the nuclear spin precession dynamics via an external magnetic field and nuclear spin polarization, it is possible to manipulate the dynamical behavior of the electron spin, showing a transition between classicality and nonclassicality. We propose an explanation of the classicality–nonclassicality transition in terms of the nuclear spin precession axis orientation and dynamics. We have also performed a series of numerical simulations supporting our findings. Consequently, we can attribute the nonclassical trait of the electron spin dynamics to the behavior of nuclear spin precession dynamics.

Classical dynamics from self-consistency equations in quantum mechanics

During the last three decades, Pavel Bóna developed a non-linear generalization of quantum mechanics, which is based on symplectic structures for normal states. One important application of such a generalization is a general setting that is very convenient to study the emergence of macroscopic classical dynamics from microscopic quantum processes. We propose here a new mathematical approach to Bóna’s non-linear quantum mechanics. It is based on C0-semigroup theory and has a domain of applicability that is much broader than Bóna’s original one. It highlights the central role of self-consistency. This leads to a mathematical framework in which the classical and quantum worlds are naturally entangled. In this new mathematical approach, we build a Poisson bracket for the polynomial functions on the Hermitian weak*-continuous functionals on any C*-algebra. This is reminiscent of a well-known construction for finite-dimensional Lie algebras. We then restrict this Poisson bracket to states of this C*-algebra by taking quotients with respect to Poisson ideals. This leads to densely defined symmetric derivations on the commutative C*-algebras of real-valued functions on the set of states. Up to a closure, these are proven to generate C0-groups of contractions. As a matter of fact, in generic commutative C*-algebras, even the closableness of unbounded symmetric derivations is a non-trivial issue. Some new mathematical concepts are introduced, which are possibly interesting by themselves: the convex weak* Gâteaux derivative and the state-dependent C*-dynamical systems. Our recent results on macroscopic dynamical properties of lattice-fermion and quantum-spin systems with long-range, or mean-field, interactions corroborate the relevance of the general approach we present here.

Introduction

Previous articleNext article FreeIntroductionPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreThe four articles in this issue address debates about early modern women’s authorship, refocus our attention on forgotten historical women, assess their forays into male-dominated literary worlds, and recover the works of religious women in genres generally deemed secular. Jake Arthur, in “Anne Lock or Thomas Norton? A Response to the Reattribution of the First Sonnet Sequence in English,” intervenes in the debate over “A Meditation of a Penitent Sinner” (1560), arguing that Anne Lock was the most likely author of this text. Estelle Paranque, in “Devotion, Influence, and Loyalty: Reevaluating Queen Louise de Lorraine-Vaudémont’s Political and Diplomatic Role in Early Modern France,” uses the correspondence of this overshadowed sixteenth-century royal woman to counter the assumption that Louise did not engage in politics. Sara Diaz, in “Exceptional Bodies and Ludic Lovers: Humor, Disability, and the Grotesque in Margherita Costa’s Lettere amorose (1639),” explores Costa’s foray into the male-dominated world of Italian ludic literature through her epistolary collection, which features an unprecedented complementarity between sexed and comically embodied voices. Anna-Lisa Halling, in “Soror Maria do Céu’s Aves Illustradas: A Conduct Manual Legitimizing Female Authority for Early Modern Nuns through Storytelling,” turns to the Portuguese context to analyze an early eighteenth-century conduct manual for nuns that relies on narrative rather than rules to guide their comportment and spiritual advancement. Each of these early modern women authors reminds us of the myriad ways that women used writing as a mechanism not only to assert their ideas but also to demonstrate the centrality of women’s activities and influence in early modern society.Adding to this array of articles across disciplines and national cultures, we feature book reviews that cover women’s engagement in art, marriage, motherhood, court culture, rule, authorship, and patronage, to note only a few representative topics. The geographical range of the subjects covers England, France, Italy, Spain, and the Low Countries, as well as the classical worlds of Greece and Rome. We include a performance review of Margaret Cavendish’s The Unnatural Tragedy, performed at the University of Vienna in 2020, and welcome suggestions for reviews of other performances and multimedia productions.Finally, with the recent move to the University of Chicago Press and our new affiliation with the Society for the Study of Early Modern Women and Gender, we have taken the opportunity to bring some important changes to Early Modern Women. As some of you may have noticed in the last issue, we have engaged a more diverse set of scholars for our editorial and advisory boards. We are also working to ensure that upcoming issues will include more articles about non-European women of various religions, races, and classes, as well as racialized women within Europe. In volume 17, we will begin what we hope is an ongoing conversation about early modern women and race across disciplines. We are reaching out to a more diverse and global group of reviewers and are reviewing more books about women outside of Europe. We are excited about the future and believe that these changes are integral to ensuring that Early Modern Women continues to be a vibrant voice for scholars in our field. Previous articleNext article DetailsFiguresReferencesCited by Early Modern Women: An Interdisciplinary Journal Volume 16, Number 2Spring 2022 Published for the Society for the Study of Early Modern Women and Gender Article DOIhttps://doi.org/10.1086/718296 Views: 596 © 2022 Society for the Study of Early Modern Women and Gender. All rights reserved.PDF download Crossref reports no articles citing this article.

Light Cones as Quantum Phenomena

Quantum erasure experiments push the boundary between the quantum and classical worlds by letting delayed events influence the state of previously recorded and potentially widely distributed classical information. The only significant restriction to such unsettling violations of forward-only causality is that the distribution of forward-dependent information cannot cross out of the light cone boundaries of the event in the past, a feature that ensures no violations of causality — no rewriting of anyone else's recorded histories — can occur. The erasure interpretation of this conundrum requires rewriting of information recorded and distributed in the past, which would itself be a violation of causality. The quantum predestination interpretation removes the causal rewriting issue. However, quantum predestination requires detailed coordination of inputs from outside of the forward-dependent event's light cone, thus massively violating the same limit that prevents causality violations in such events. Yet another approach is to invoke the Schrödinger's cat variant of quantum erasure in which arbitrarily complex classical events within the light cone become quantum dependent upon the future event. As with all Schrödinger's cat interpretations of quantum mechanics, this variant of quantum erasure violates causality by discarding local classical histories such as the information-rich state of the cat's body. The most straightforward interpretation of erasure experiments is to follow the lead of the equations themselves, which transform on paper as if their components are independent of ordinary space and time limits, up to the limits imposed on them by the speed of light. Interpreting the light cone of each quantum system as an atemporal, aspatial unit in which classical time and space have no meaning results in a multi-scale, matter-dependent definition of spacetime in which every light cone is a singular quantum entity. In such a universe, both time and space are defined not as pre-existing, mass-independent continuums but as the consensus of vast numbers of constantly interacting and mutually limiting quantum-entity light cones.

Entanglement of classical and quantum short-range dynamics in mean-field systems

The relationship between classical and quantum mechanics is usually understood via the limit ħ→0. This is the underlying idea behind the quantization of classical objects. The apparent incompatibility of general relativity with quantum mechanics and quantum field theory has challenged for many decades this basic idea. We recently showed (Bru and de Siqueira Pedra, 0000; Bru and de Siqueira Pedra, 2021 [46,47]) the emergence of classical dynamics for very general quantum lattice systems with mean-field interactions, without (complete) suppression of its quantum features, in the infinite volume limit. This leads to a theoretical framework in which the classical and quantum worlds are entangled. Such an entanglement is noteworthy and is a consequence of the highly non-local character of mean-field interactions. Therefore, this phenomenon should not be restricted to systems with mean-field interactions only, but should also appear in presence of interactions that are sufficiently long-range, yielding effective, classical background fields, in the spirit of the Higgs mechanism of quantum field theory. In order to present the result in a less abstract way than in its original version, here we apply it to a concrete, physically relevant, example and discuss, by this means, various important aspects of our general approach. The model we consider is not exactly solvable and the particular results obtained are new.

Random generators of Markovian evolution: A quantum-classical transition by superdecoherence.

Continuous-time Markovian evolution appears to be manifestly different in classical and quantum worlds. We consider ensembles of random generators of N-dimensional Markovian evolution, quantum and classical ones, and evaluate their universal spectral properties. We then show how the two types of generators can be related by superdecoherence. In analogy with the mechanism of decoherence, which transforms a quantum state into a classical one, superdecoherence can be used to transform a Lindblad operator (generator of quantum evolution) into a Kolmogorov operator (generator of classical evolution). We inspect spectra of random Lindblad operators undergoing superdecoherence and demonstrate that, in the limit of complete superdecoherence, the resulting operators exhibit spectral density typical to random Kolmogorov operators. By gradually increasing strength of superdecoherence, we observe a sharp quantum-to-classical transition. Furthermore, we define an inverse procedure of supercoherification that is a generalization of the scheme used to construct a quantum state out of a classical one. Finally, we study microscopic correlation between neighboring eigenvalues through the complex spacing ratios and observe the horseshoe distribution, emblematic of the Ginibre universality class, for both types of random generators. Remarkably, it survives both superdecoherence and supercoherification.

Decoherence effects break reciprocity in matter transport

The decoherence of quantum states defines the transition between the quantum world and classical physics. Decoherence or, analogously, quantum mechanical collapse events pose fundamental questions regarding the interpretation of quantum mechanics and are technologically relevant because they limit the coherent information processing performed by quantum computers. We have discovered that the transition regime enables a novel type of matter transport. Applying this discovery, we present nanoscale devices in which decoherence, modeled by random quantum jumps, produces fundamentally novel phenomena by interrupting the unitary dynamics of electron wave packets. Noncentrosymmetric conductors with mesoscopic length scales act as two-terminal rectifiers with unique properties. In these devices, the inelastic interaction of itinerant electrons with impurities acting as electron trapping centers leads to a novel steady state characterized by partial charge separation between the two leads, or, in closed circuits to the generation of persistent currents. The interface between the quantum and the classical worlds therefore provides a novel transport regime of value for the realization of a new category of mesoscopic electronic devices.

Direct observation of deterministic macroscopic entanglement

Quantum entanglement of mechanical systems emerges when distinct objects move with such a high degree of correlation that they can no longer be described separately. Although quantum mechanics presumably applies to objects of all sizes, directly observing entanglement becomes challenging as masses increase, requiring measurement and control with a vanishingly small error. Here, using pulsed electromechanics, we deterministically entangle two mechanical drumheads with masses of 70 picograms. Through nearly quantum-limited measurements of the position and momentum quadratures of both drums, we perform quantum state tomography and thereby directly observe entanglement. Such entangled macroscopic systems are poised to serve in fundamental tests of quantum mechanics, enable sensing beyond the standard quantum limit, and function as long-lived nodes of future quantum networks.

Quantum mechanics-free subsystem with mechanical oscillators.

Quantum mechanics sets a limit for the precision of continuous measurement of the position of an oscillator. We show how it is possible to measure an oscillator without quantum back-action of the measurement by constructing one effective oscillator from two physical oscillators. We realize such a quantum mechanics-free subsystem using two micromechanical oscillators, and show the measurements of two collective quadratures while evading the quantum back-action by 8 decibels on both of them, obtaining a total noise within a factor of 2 of the full quantum limit. This facilitates the detection of weak forces and the generation and measurement of nonclassical motional states of the oscillators. Moreover, we directly verify the quantum entanglement of the two oscillators by measuring the Duan quantity 1.4 decibels below the separability bound.