Classical Worlds Research Articles

Filling the gap between the quantum and classical worlds of nanoscale magnetism: giant molecular aggregates based on paramagnetic 3d metal ions.

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

Even- and odd-order dispersion cancellation effects in a two-photon interferometer

Dispersion cancellation effects have attracted much attention in both classical and quantum worlds. In this paper, we show that by implementing a delicate design in a Mach–Zehnder (MZ) interferometer, we can observe the cancellation of even- and odd-order dispersion by twisting the polarizers placed in front of two single-photon detectors. This polarization post-selection scheme demonstrates that the classical and quantum interferogram can be obtained in different cases in a single MZ interferometer.

An Update on Epistemic Modals

Epistemic modals are a prominent topic in the literature on natural language semantics, with wide-ranging implications for issues in philosophy of language and philosophical logic. Considerations about the role that epistemic might and must play in discourse and reasoning have led to the development of several important alternatives to classical possible worlds semantics for natural language modal expressions. This is an opinionated overview of what I take to be some of the most exciting issues and developments in the eld.

A quantum world arising from many ordinary ones

Radical theory proposes that interactions between classical worlds can explain some quantum phenomena.

Quantum Phenomena Modeled by Interactions between Many Classical Worlds

Researchers propose a new ``many-interacting-worlds'' theory that could explain quantum mechanics in all its strangeness. Numerical simulations reproduce wave behavior in double-slit experiments assuming as few as 40 worlds.

Which came first, spacetime or clocks?

Emergent quantum mechanics seeks a deeper level theory, anticipating that such a theory will provide a clearer picture of the relation between the quantum and classical worlds. In this work we show that the quantum-classical divide is a manifestation of the transition from Newton's absolute time to relativity's path-dependent time. The prior theory in this case is that particles are intrinsic clocks. The emergence of separate classical and quantum behaviour is seen by considering different continuum limits in a single digital clock model. A continuum limit that constructs a continuous worldline provides a simple basis for Minkowski spacetime. An alternative limit in which the clock itself contains boost information leads to the Dirac equation.

Dragons, serpents, and slayers in the classical and early Christian worlds: a sourcebook

Dedication Acknowledgements List of Figures Abbreviations Quick Key to Some Special Terms and Conventions Used in this Book Introduction Schema of motifs PART ONE: THE CLASSICAL DRAGON i. The Genealogy of the Great Dragons ii. Typhon, Slain by Zeus iii. Python, Slain by Apollo iv. Heracles' Dragons (i): Baby Heracles and the Dragon-pair Sent by Hera v. Heracles' Dragons (ii): the Hydra vi. Heracles' Dragons (iii): Ladon, the Dragon of the Hesperides vii. Heracles' Dragons (iv): Cerberus, the Hound of Hades viii. The Chimaera, Slain by Bellerophon ix. Medusa, Slain by Perseus x. Lamia, Slain by Eurybatus and Others xi. The Dragon of Ares, Slain by Cadmus xii. The Dragon of Nemea, Slain by the Seven against Thebes xiii. The Dragon of Colchis, Slain or Put to Sleep by Jason and Medea xiv. The Dragon-pair Sent against Laocoon and his Sons xv. The Dragon of the River Bagrada, Slain by Regulus and his Army xvi. Some Unique Dragon-slaying and Dragon-averting Narratives in Later Greek Sources xvii. The Sea-monster of Troy, Slain by Heracles xviii. The Sea-Serpent of Ethiopia, Slain by Perseus xix. Scylla, Slain by Heracles and Encountered by Odysseus PART TWO: THE CHRISTIAN DRAGON xx. The Serpents of the Bible and its Apocrypha xxi. The Dragons of the Early Hagiographical Tradition xxii. St Philip, the Echidna and the Ophianoi xxiii. St Silvester and the Dragon of Rome xxiv. Saintly Tales Originating between the Fourth and Sixth Centuries AD xxv. Saintly Tales of the Central Medieval Period xxvi. St Patrick and St George APPENDICES Appendix A: World-foundational Dragon-slaying Tales from the Ancient Near East and India Appendix B: Germanic Dragon fights of the eighth to thirteenth centuries AD Appendix C: A Selection of Dragon- and Serpent-slaying Tales of Folkloric Interest List of Editions Used References Source Index General Index

Quantum Illumination The Quantum Divide Why Schrödinger's Cat Is Either Dead or Alive by Christopher Gerry and Kimberley Bruno Oxford University Press, Oxford, 2013. 207 pp. $44.95, £25. ISBN 9780199666560.

Surveying key experimental findings from the past three decades, the authors explore links between the microscopic quantum and macroscopic classical worlds.

Entang-bling: Observing quantum correlations in room-temperature solids

Quantum entanglement in the motion of macroscopic solid bodies has implications both for quantum technologies and foundational studies of the boundary between the quantum and classical worlds. Entanglement is usually fragile in room-temperature solids, owing to strong interactions both internally and with the noisy environment. We generated motional entanglement between vibrational states of two spatially separated, millimeter-sized diamonds at room temperature. By measuring strong nonclassical correlations between Raman-scattered photons, we showed that the quantum state of the diamonds has positive concurrence with 98% probability. Our results show that entanglement can persist in the classical context of moving macroscopic solids in ambient conditions.

Quantum data gathering

Measurement of a quantum system – the process by which an observer gathers information about it – provides a link between the quantum and classical worlds. The nature of this process is the central issue for attempts to reconcile quantum and classical descriptions of physical processes. Here, we show that the conventional paradigm of quantum measurement is directly responsible for a well-known disparity between the resources required to extract information from quantum and classical systems. We introduce a simple form of quantum data gathering, “coherent measurement”, that eliminates this disparity and restores a pleasing symmetry between classical and quantum statistical inference. To illustrate the power of quantum data gathering, we demonstrate that coherent measurements are optimal and strictly more powerful than conventional one-at-a-time measurements for the task of discriminating quantum states, including certain entangled many-body states (e.g., matrix product states).

Limits of privacy amplification against nonsignaling memory attacks

The task of privacy amplification, in which Alice holds some partially secret information with respect to an adversary Eve and wishes to distill it until it is completely secret, is known to be solvable almost optimally in both the classical and quantum worlds. Unfortunately, when considering an adversary who is limited only by nonsignaling constraints such a statement cannot be made in general. We here consider systems which violate the chained Bell inequality and prove that under the natural assumptions of a time-ordered nonsignaling system, which allow past subsystems to signal future subsystems (using the device's memory for example), superpolynomial privacy amplification by any hashing is impossible. This is of great relevance when considering practical device-independent key-distribution protocols which assume a superquantum adversary.

The classical-quantum boundary for correlations: Discord and related measures

One of the best signatures of nonclassicality in a quantum system is the existence of correlations that have no classical counterpart. Different methods for quantifying the quantum and classical parts of correlations are amongst the more actively-studied topics of quantum information theory over the past decade. Entanglement is the most prominent of these correlations, but in many cases unentangled states exhibit nonclassical behavior too. Thus distinguishing quantum correlations other than entanglement provides a better division between the quantum and classical worlds, especially when considering mixed states. Here we review different notions of classical and quantum correlations quantified by quantum discord and other related measures. In the first half, we review the mathematical properties of the measures of quantum correlations, relate them to each other, and discuss the classical-quantum division that is common among them. In the second half, we show that the measures identify and quantify the deviation from classicality in various quantum-information-processing tasks, quantum thermodynamics, open-system dynamics, and many-body physics. We show that in many cases quantum correlations indicate an advantage of quantum methods over classical ones.

Stabilizing Rabi oscillations in a superconducting qubit using quantum feedback

The act of measurement bridges the quantum and classical worlds by projecting a superposition of possible states into a single (probabilistic) outcome. The timescale of this 'instantaneous' process can be stretched using weak measurements, such that it takes the form of a gradual random walk towards a final state. Remarkably, the interim measurement record is sufficient to continuously track and steer the quantum state using feedback. Here we implement quantum feedback control in a solid-state system, namely a superconducting quantum bit (qubit) coupled to a microwave cavity. A weak measurement of the qubit is implemented by probing the cavity with microwave photons, maintaining its average occupation at less than one photon. These photons are then directed to a high-bandwidth, quantum-noise-limited amplifier, which allows real-time monitoring of the state of the cavity (and, hence, that of the qubit) with high fidelity. We demonstrate quantum feedback control by inhibiting the decay of Rabi oscillations, allowing them to persist indefinitely. Such an ability permits the active suppression of decoherence and enables a method of quantum error correction based on weak continuous measurements. Other applications include quantum state stabilization, entanglement generation using measurement, state purification and adaptive measurements.

ChemInform Abstract: Single‐Molecule Nanomagnets

AbstractReview: 132 refs.

On Quantum Effects in a Theory of Biological Evolution

We construct a descriptive toy model that considers quantum effects on biological evolution starting from Chaitin's classical framework. There are smart evolution scenarios in which a quantum world is as favorable as classical worlds for evolution to take place. However, in more natural scenarios, the rate of evolution depends on the degree of entanglement present in quantum organisms with respect to classical organisms. If the entanglement is maximal, classical evolution turns out to be more favorable.

Tuned Transition from Quantum to Classical for Macroscopic Quantum States

The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. Here we employ a tunable flux qubit with basis states having persistent currents of 1 μA carried by a million pairs of electrons. By tuning the tunnel barrier between these states we see a crossover from quantum to classical. Released from nonequilibrium, the system exhibits spontaneous coherent oscillations. For high barriers the lifetime of the states increases dramatically while the tunneling period approaches the phase coherence time and the oscillations fade away.

Quantum measurements between a single spin and a torsional nanomechanical resonator

While the motions of macroscopic objects must ultimately be governed by quantum mechanics, the distinctive features of quantum mechanics can be hidden or washed out by thermal excitations and coupling to the environment. We propose a system consisting of a graphene nanomechanical oscillator (NMO) coupled with a single spin through a uniform external magnetic field, which could become the building block for a wide range of quantum nanomechanical devices. The choice of graphene as the NMO material is critical for minimizing the moment of inertia of the oscillator. The spin originates from a nitrogen-vacancy (NV) center in a diamond nanocrystal that is positioned on the NMO. This coupling results in quantum non-demolition (QND) measurements of the oscillator and spin states, enabling a bridge between the quantum and classical worlds for a simple readout of the NV center spin and observation of the discrete states of the NMO.

The Call of Vocation inJulius CaesarandCoriolanus

In the classical worlds of Julius Caesar and Coriolanus Shakespeare finds the conditions in which to isolate and analyze the Christian doctrine of vocation, the idea that individuals are destined to fill a place in the body politic or the congregation of believers. Many of Shakespeare's plays pit character against calling. In the Roman tragedies the tension is especially acute. The principals struggle to discern a call in a world dismembered by revolution to the point that a voice can come from a wound. Repeatedly, civic turmoil is described in terms of creation and apocalypse; vocation, hinted at through plot turns and Pauline phrasing, should span and structure the interim. But both plays present a monolithic title character whose all‐consuming integrity threatens to annihilate the society that produced him. Under the pressure of events, Brutus' identity splits, while his co‐conspirators scramble for parts that suddenly seem too few to go around. Coriolanus despises “the many” and their trades that seem fractious and fragmentary next to his self‐sufficiency. Vocational uncertainty triggers other theological conundrums, such as free will and Christian liberty. At still another level, the theatrical imagery of the plays calls into question Shakespeare's own vocation as dramatist. (R. M.)

Single-Molecule Nanomagnets

Single-molecule magnets straddle the classical and quantum mechanical worlds, displaying many fascinating phenomena. They may have important technological applications in information storage and quantum computation. We review the physical properties of two prototypical molecular nanomagnets, Mn12-acetate and Fe8: Each behaves as a rigid, spin-10 object and exhibits tunneling between up and down directions. As temperature is lowered, the spin-reversal process evolves from thermal activation to pure quantum tunneling. At low temperatures, magnetic avalanches occur in which the magnetization of an entire sample rapidly reverses. We discuss the important role that symmetry-breaking fields play in driving tunneling and in producing Berry-phase interference. Recent experimental advances indicate that quantum coherence can be maintained on timescales sufficient to allow a meaningful number of quantum computing operations to be performed. Efforts are under way to create monolayers and to address and manipulate individual molecules.

A macroscopic mechanical resonator driven by mesoscopic electrical back-action

Systems with coupled mechanical and optical or electrical degrees of freedom have fascinating dynamics that, through macroscopic manifestations of quantum behaviour, provide new insights into the transition between the classical and quantum worlds. Of particular interest is the back-action of electrons and photons on mechanical oscillators, which can lead to cooling and amplification of mechanical motion. Furthermore, feedback, which is naturally associated with back-action, has been predicted to have significant consequences for the noise of a detector coupled to a mechanical oscillator. Recently it has also been demonstrated that such feedback effects lead to strong coupling between single-electron transport and mechanical motion in carbon nanotube nanomechanical resonators. Here we present noise measurements which show that the mesoscopic back-action of electrons tunnelling through a radio-frequency quantum point contact causes driven vibrations of the host crystal. This effect is a remarkable macroscopic manifestation of microscopic quantum behaviour, where the motion of a mechanical oscillator-the host crystal, which consists of on the order of 10(20) atoms-is determined by statistical fluctuations of tunnelling electrons.