Aspects Of Quantum Mechanics Research Articles

A new introductory quantum mechanics curriculum

The Institute of Physics New Quantum Curriculum consists of freely available online learning and teaching materials (quantumphysics.iop.org) for a first course in university quantum mechanics starting from two-level systems. This approach immediately immerses students in inherently quantum-mechanical aspects by focusing on experiments that have no classical explanation. It allows from the start a discussion of the interpretive aspects of quantum mechanics and quantum information theory. This paper gives an overview of the resources available from the IOP website. The core text includes around 80 articles which are co-authored by leading experts, arranged in themes, and can be used flexibly to provide a range of alternative approaches. Many of the articles include interactive simulations with accompanying activities and problem sets that can be explored by students to enhance their understanding. Much of the linear algebra needed for this approach is included in the resource. Solutions to activities are available to instructors. The resources can be used in a variety of ways, from being supplemental to existing courses to forming a complete programme.

Three-Slit Experiments and Quantum Nonlocality

An interesting link between two very different physical aspects of quantum mechanics is revealed; these are the absence of third-order interference and Tsirelson's bound for the nonlocal correlations. Considering multiple-slit experiments - not only the traditional configuration with two slits, but also configurations with three and more slits - Sorkin detected that third-order (and higher-order) interference is not possible in quantum mechanics. The EPR experiments show that quantum mechanics involves nonlocal correlations which are demonstrated in a violation of the Bell or CHSH inequality, but are still limited by a bound discovered by Tsirelson. It now turns out that Tsirelson's bound holds in a broad class of probabilistic theories provided that they rule out third-order interference. A major characteristic of this class is the existence of a reasonable calculus of conditional probability or, phrased more physically, of a reasonable model for the quantum measurement process.

Experimental realization of non-Abelian non-adiabatic geometric gates

The geometric aspects of quantum mechanics are emphasized most prominently by the concept of geometric phases, which are acquired whenever a quantum system evolves along a path in Hilbert space, that is, the space of quantum states of the system. The geometric phase is determined only by the shape of this path and is, in its simplest form, a real number. However, if the system has degenerate energy levels, then matrix-valued geometric state transformations, known as non-Abelian holonomies--the effect of which depends on the order of two consecutive paths--can be obtained. They are important, for example, for the creation of synthetic gauge fields in cold atomic gases or the description of non-Abelian anyon statistics. Moreover, there are proposals to exploit non-Abelian holonomic gates for the purposes of noise-resilient quantum computation. In contrast to Abelian geometric operations, non-Abelian ones have been observed only in nuclear quadrupole resonance experiments with a large number of spins, and without full characterization of the geometric process and its non-commutative nature. Here we realize non-Abelian non-adiabatic holonomic quantum operations on a single, superconducting, artificial three-level atom by applying a well-controlled, two-tone microwave drive. Using quantum process tomography, we determine fidelities of the resulting non-commuting gates that exceed 95 per cent. We show that two different quantum gates, originating from two distinct paths in Hilbert space, yield non-equivalent transformations when applied in different orders. This provides evidence for the non-Abelian character of the implemented holonomic quantum operations. In combination with a non-trivial two-quantum-bit gate, our method suggests a way to universal holonomic quantum computing.

Everett Interpretation and Quantum Concept of Consciousness

Subjective aspects of quantum mechanics (QM) are most radically expressed in the (EI) of QM which suggests coexisting macroscopically distinct configurations of the world in the form of a superposition of the (quasi-)classical state vectors. The components of such a superposition are often verbally denoted as Everett's worlds, hence the name Many-Worlds Interpretation (MWI) for EI. Explicit accounting the correlation of each classical configuration of the world with the corresponding state of an observer's mind yields the so-called Many-Minds interpretation (MMI). This is maximum that may be done in the context of EI if the restriction by pure physics is implied. In the author's Extended Everett Concept (EEC) the observer's consciousness is defined in the spirit of psycho-physical parallelism, i.e. as going beyond pure physics. As a consequence, according to EEC, an observer, if he/she weakens or turns off his/her consciousness (perception), obtains the ability of super-intuition (obtaining seemingly unavailable information) and even of controlling the subjective reality (a picture of classical reality as it will be subjectively perceived). This may be interpreted as a realization of the Jung's collective unconscious as well as an explanation of the mystical elements in Oriental philosophies, world religions and deep psychological practices. NeuroQuantology | March 2013 | Vol 11 | Issue 1 | Suppl 1 | Page 85-96

Observation of Entanglement between Itinerant Microwave Photons and a Superconducting Qubit

A localized qubit entangled with a propagating quantum field is well suited to study nonlocal aspects of quantum mechanics and may also provide a channel to communicate between spatially separated nodes in a quantum network. Here, we report the on-demand generation and characterization of Bell-type entangled states between a superconducting qubit and propagating microwave fields composed of zero-, one-, and two-photon Fock states. Using low noise linear amplification and efficient data acquisition we extract all relevant correlations between the qubit and the photon states and demonstrate entanglement with high fidelity.

On the Lattice Structure of Probability Spaces in Quantum Mechanics

Let C be the set of all possible quantum states. We study the convex subsets of C with attention focused on the lattice theoretical structure of these convex subsets and, as a result, find a framework capable of unifying several aspects of quantum mechanics, including entanglement and Jaynes' Max-Ent principle. We also encounter links with entanglement witnesses, which leads to a new separability criteria expressed in lattice language. We also provide an extension of a separability criteria based on convex polytopes to the infinite dimensional case and show that it reveals interesting facets concerning the geometrical structure of the convex subsets. It is seen that the above mentioned framework is also capable of generalization to any statistical theory via the so-called convex operational models' approach. In particular, we show how to extend the geometrical structure underlying entanglement to any statistical model, an extension which may be useful for studying correlations in different generalizations of quantum mechanics.

Large quantum probability backflow and the azimuthal angle–angular momentum uncertainty relation for an electron in a constant magnetic field

In this paper we demonstrate a surprising aspect of quantum mechanics that is accessible to an undergraduate student. We discuss probability backflow for an electron in a constant magnetic field. It is shown that even for a wavepacket composed entirely of states with negative angular momentum the effective angular momentum can take on positive values in some regions of space. This is also a demonstration of the azimuthal angle–angular momentum uncertainty relation. This example is chosen because the backflow motion persists indefinitely. However this work can easily be extended to other systems where the motion is notionally circular, such as the hydrogen atom.

Conjugate dynamical systems: classical analogue of the quantum energy translation

An aspect of quantum mechanics that has not been fully understood is the energy shift generated by the time operator. In this study, we introduce the use of the eigensurfaces of dynamical variables and commutators in classical mechanics to study the classical analogue of the quantum translation of energy. We determine that there is a conjugate dynamical system that is conjugate to Hamilton's equations of motion, and then we generate the analogue of the time operator and use it in the translation of points along the energy direction, i.e. the classical analogue of the Pauli theorem. The theory is illustrated with a nonlinear oscillator model.

The Lagrangian and Hamiltonian Aspects of the Electrodynamic Vacuum-Field Theory Models

The important classical Ampere’s and Lorentz laws derivations are revisited and their relationships with the modern vacuum field theory approach to modern relativistic electrodynamics are demonstrated. The relativistic models of the vacuum field medium and charged point particle dynamics as well as related classical electrodynamics problems jointly with the fundamental principles, characterizing the electrodynamical vacuum-field structure, based on the developed field theory concepts are reviewed and analyzed detail. There is also described a new approach to the classical Maxwell theory based on the derived and newly interpreted basic equations making use of the vacuum field theory approach. There are obtained the main classical special relativity theory relationships and their new explanations. The well known Feynman approach to Maxwell electromagnetic equations and the Lorentz type force derivation is also. A related charged point particle dynamics and a hadronic string model analysis is also presented. We also revisited and reanalyzed the classical Lorentz force expression in arbitrary non-inertial reference frames and present some new interpretations of the relations between special relativity theory and its quantum mechanical aspects. Some results related with the charge particle radiation problem and the magnetic potential topological aspects are discussed. The electromagnetic Dirac-Fock-Podolsky problem of the Maxwell and Yang-Mills type dynamical systems is analyzed within the classical Dirac-Marsden-Weinstein symplectic reduction theory. Based on the Gelfand-Vilenkin representation theory of infinite dimensional groups and the Goldin-Menikoff-Sharp theory of generating Bogolubov type functionals the problem of constructing Fock type representations and retrieving their creation-annihilation operator structure is analyzed. An application of the suitable current algebra representation to describing the non-relativistic Aharonov-Bohm paradox is demonstrated. The current algebra coherent functional representations are constructed and their importance subject to the linearization problem of nonlinear dynamical systems in Hilbert spaces is also presented.

A simplified calculation of power-broadened linewidths, with application to resonance ionization mass spectrometry

I present a simple derivation of the power-broadened linewidth of an optical transition in a two-level atom. The novelty of the approach lies in its flexibility, as the approach described here can be applied to any spectral lineshape, corresponding to either homogeneous or inhomogeneous broadening mechanisms. For a Lorentzian profile, I recover the same dependence of linewidth on laser power that one calculates from the optical Bloch equations. The present treatment makes explicit that power broadening arises because of the saturability of the atomic response to intense lasers, rather than to explicitly quantum mechanical aspects of the laser–atom interaction, all of which are ignored. I discuss the utility of power broadening in resonance ionization mass spectrometry, where it is an important means of mitigating unwanted instrumental isotope fractionation.

Indistinguibilidade, não reflexividade, ontologia e física quântica

It has been taken as reasonable to assume that, insofar as we deal with objects that lie beyond the formalism of physical theories, quantum physics commits us to an ontology of entities that can be assumed to be both absolutely indistinguishable and, in a sense, as lacking individuality. In this article, first, we briefly and generally consider the nature of this commitment, by discussing how it can be understood in metaphysical terms, as well as its relationship with the logical systems employed to talk about the objects to which we are committed. Then we present some of the main aspects of orthodox quantum mechanics that are usually employed to provide arguments for suggesting an ontology of objects having these features, that is, of objects that are both indistinguishable and have no individuality. Finally, we sketch the main features of quasi-set theory, a system of set theory, for the purpose of capturing formally these features in a natural way, and for employing it as the underlying logic for grounding a metaphysics of non-individuals.

Nonlinear spectroscopy of superconducting anharmonic resonators

We formulate a model for the steady state response of a nonlinear quantum oscillator structure, such as those used in a variety of superconducting qubit experiments, when excited by a steady, but not necessarily small, ac tone. We show that this model can be derived directly from a circuit description of some recent qubit experiments in which the state of the qubit is read out directly, without a superconducting quantum interference device (SQUID) magnetometer. The excitation profile has a rich structure depending on the detuning of the tone from the small-signal resonant frequency, on the degree of damping and on the excitation amplitude. We explore two regions in detail. Firstly, at high damping there is a trough in the excitation response as a function of detuning, near where the classical Duffing bifurcation occurs. This trough has been understood as a classical interference between two metastable responses with opposite phase. We use Wigner function studies to show that while this picture is roughly correct, there are also more quantum mechanical aspects to this feature. Secondly, at low damping we study the emergence of sharp, discrete spectral features from a continuum response. We show that these the structures, associated with discrete transitions between different excited-state eigenstates of the oscillator, provide an interesting example of a quantum Fano resonance. The trough in the Fano response evolves continuously from the ‘classical’ trough at high damping.

Quantum mechanical aspects of cell microtubules: science fiction or realistic possibility?

Recent experimental research with marine algae points towards quantum entanglement at ambient temperature, with correlations between essential biological units separated by distances as long as 20 Angströms. The associated decoherence times, due to environmental influences, are found to be of order 400 fs. This prompted some authors to connect such findings with the possibility of some kind of quantum computation taking place in these biological entities: within the decoherence time scales, the cell "quantum calculates" the optimal "path" along which energy and signal would be transported more efficiently. Prompted by these experimental results, in this talk I remind the audience of a related topic proposed several years ago in connection with the possible rôle of quantum mechanics and/or field theory on dissipation-free energy transfer in microtubules (MT), which constitute fundamental cell substructures. The basic assumption was to view the cell MT as quantum electrodynamical cavities, providing sufficient isolation in vivo to enable the formation of electric-dipole quantum coherent solitonic states across the tubulin dimer walls. Crucial to this, were argued to be the electromagnetic interactions of the dipole moments of the tubulin dimers with the dipole quanta in the ordered water interiors of the MT, that play the rôle of quantum coherent cavity modes. Quantum entanglement between tubulin dimers was argued to be possible, provided there exists sufficient isolation from other environmental cell effects. The model was based on certain ferroelectric aspects of MT. Subsequent experiments in vitro could not confirm ferroelectricity at room temperatures, however they provided experimental measurements of the induced electric dipole moments of the MT under the influence of external electric fields. Nevertheless, this does not demonstrate that in vivo MT are not ferroelectric materials. More refined experiments should be done. In the talk I review the model and the associated experimental tests so far and discuss future directions, especially in view of the algae photo-experiments.

MIMICKING QUANTUM MECHANICS USING REACTIVE PROGRAMMING

We implement in a reactive programming framework a system mimicking three aspects of quantum mechanics: self-interference, state superposition, and entanglement. The system basically consists in a cellular automaton embedded in a synchronous environment which defines global discrete instants and broadcast events. The implementation shows how a simulation of fundamental aspects of quantum mechanics can be obtained from the synchronous parallel combination of a small number of elementary components.

From Wave-Particle to Features-Event Complementarity

The terms wave and particle are of classical origin and are inadequate in dealing with the novelties of quantum mechanics with respect to classical physics. In this paper we propose to substitute the wave-particle terminology with that of features-event complementarity. This approach aims at solving some of the problems affecting quantum-mechanics since its birth. In our terminology, features are what is responsible for one of the most characterizing aspects of quantum mechanics: quantum correlations. We suggest that an (uninterpreted) basic ontology for quantum mechanics should be thought of as constituted by events, features and their dynamical interplay, and that its (interpreted) theoretical ontology (made up by three classes of theoretical entities: states, observables and properties) does not isomorphically correspond to the uninterpreted ontology. Operations, i.e. concrete interventions within the physical world, like preparation, premeasurement and measurement, together with reliable inferences, assure the bridge between interpreted and uninterpreted ontology.

Nilpotent quantum mechanics and SUSY

Formalism where fundamental variables are nilpotent, but in contrast to the super-mathematics, not anticommutative but commutative gives another version of realization of the Pauli exclusion principle. We discuss some aspects of nilpotent quantum mechanics realized in generalized Hilbert space of functions of nilpotent commuting variables. The qubits are natural objects described by such a formalism. Supersymmetric system of qubit and fermion is presented.

Time-symmetric quantum mechanics questioned and defended

Time-symmetric quantum mechanics questioned and defended

High efficiency coherent optical memory with warm rubidium vapour

By harnessing aspects of quantum mechanics, communication and information processing could be radically transformed. Promising forms of quantum information technology include optical quantum cryptographic systems and computing using photons for quantum logic operations. As with current information processing systems, some form of memory will be required. Quantum repeaters, which are required for long distance quantum key distribution, require quantum optical memory as do deterministic logic gates for optical quantum computing. Here, we present results from a coherent optical memory based on warm rubidium vapour and show 87% efficient recall of light pulses, the highest efficiency measured to date for any coherent optical memory suitable for quantum information applications. We also show storage and recall of up to 20 pulses from our system. These results show that simple warm atomic vapour systems have clear potential as a platform for quantum memory.

Vedral, V.: Decoding Reality: the Universe as Quantum Information

The book by V. Vedral, Decoding Reality: the Universe as Quantum Information, deals with one of the most interesting aspects of modern scientific research, the conceptual status and the role of information in understanding reality. The quantum revolution, which has required a radical change of our views of natural processes has also implied a basic revision of the way in which we look at information. In this sense, the subject of the book is surely relevant and timely. Some of the topics discussed by the author are stimulating and are presented in a readable and pleasant way. I have in mind, e.g. the analysis of the way in which the genetic information is preserved and transmitted as well as the description of how quantum mechanics allows an absolutely unbreakable way of secret communication. However, the real target of the book is by no means the one of making accessible to non experts the present status of the subject, the book is much more ambitious, as one can guess already from its title: Decoding Reality. Actually, its very first pages make fully clear that the aim of the author is to make understandable and compelling even for the layman (by concisely reviewing the revolutionary aspects of quantum mechanics) the fundamental fact that the informational viewpoint yields a simple solution to the most basic and challenging quests of human beings, i.e., those of understanding their origin and the one of all other things around them. It is precisely for this reason that the author feels the need to analyze various basic religious and philosophical questions. Taking into account the just mentioned intended real purpose of the book, which is made quite explicit by the author, I feel the need to present various critical remarks. In order to avoid any misunderstanding a premise is appropriate.

A New Interpretation of Quantum Mechanics

The Copenhagen interpretation is the most authorized interpretation of quantum mechanics, but there are a number of ideas that are associated with the Copenhagen interpretation. It is ceratin that this fact is not necessarily desirable. Thus, we propose a new interpretation of measurement theory, which is the linguistic aspect (or, the mathematical generalization) of quantum mechanics. Although this interpretation is superficially similar to a part of so-called Copenhagen interpretation, we show that it has a merit to be applicable to both quantum and classical systems. For example, we say that Bell’s inequality is broken even in classical systems.