6,610 research outputs found
New Perspectives on the Aharonov-Bohm Effect
No full textThe Aharonov-Bohm effect is a quantum mechanical effect, that is, has no classical counterpart. The effect was predicted in 1959 in a seminal paper of Y. Aharonov and D. Bohm [AB59] in which they demonstrated that a beam of electrons is affected by the existence of the electric/magnetic field even though electrons travel through field-free regions. Aharonov and Bohm carried out two hypothetical experiments to support their claim that potentials are more fundamental than fields and they are responsible of the effect. Since then, the debate has arisen around whether potentials are mathematical tools or fundamental entities in physics. Different arguments have been set to explain the results predicted by Aharonov and Bohm and experimentally confirmed. Amongst these arguments, the first argument adopted by Aharonov and Bohm was that potentials are physically significant. Many have claimed that fields do have non-local features, i.e. action at a distance. Others have claimed that topological effects
may interpret the effect in which potentials are modeled as connections in higher-dimensional fiber bundle geometries. The most recent argument has been proposed by Vaidman [Vai12] who claimed that the the composite system is represented by one state, an entangled state, and due to the electromagnetic interactions part of this state is changed, hence, the total state. In the present essay, I will discuss the latter argument as well as reviewing some other arguments
Locality, Lorentz invariance and the Bohm model
No full textNon-local forces exist in nature for two reasons. First that the recent experiments on locality are supposed to be accurate enough. Second that there is no local theory that can reproduce all the predictions of orthodox quantum theory which, almost for about a century, have been proved to be correct experimentally again and again. This thesis concerns both of these. A brief discussion of the measurement in quantum theory is followed by two comments which show that the quantum description is frame dependent and that the collapse of the wave-function of a system may occur without the relevant measurement being performed. After this the Bohm model and a modified version of the Bohm model are described. Next we introduce a new method for obtaining the Bell-type inequalities which can be used for testing locality. We derive more inequalities by this method than obtained by other existing procedures. Using Projection Valued(PV) and Positive Operator Valued Measures(POVM) measurements we have designed experiments which violates one of the Bell inequalities by a larger factor than existing violations which in turn could increase the accuracy of experiments to test for non-locality. This is our first result. After discussing the non-locality and non-Lorentz invariant features of the Bohm model, its retarded version, namely Squires' model - which is local and Lorentz invariant - is introduced. A problem with this model, that is the ambiguity in the cases where the wave-function depends on time, is removed by using the multiple-time wave-function. Finally, we apply the model to one of the experiments of locality and prove that it is in good agreement with the orthodox quantum theory
Solving the measurement problem: de Broglie-Bohm loses out to Everett
No full textThe quantum theory of de Broglie and Bohm solves the measurement problem, but the hypothetical corpuscles play no role in the argument. The solution finds a more natural home in the Everett interpretation
Is the electron's charge 2e? A problem of the de Broglie-Bohm theory
No full textIt is shown that the de Broglie-Bohm theory has a potential problem concerning the charge distribution of a quantum system such as an electron. According to the guidance equation of the theory, the electron's charge is localized in a position where its Bohmian particle is. But according to the Schrödinger equation of the theory, the electron's charge is not localized in one position but distributed throughout space, and the charge density in each position is proportional to the modulus square of the wave function of the electron there. Although this tension may be resolved by assuming that the electron's charge is not e but 2e, one for its Bohmian particle and the other for its wave function, the resolution will introduce more serious problems
Protective measurements and the meaning of the wave function in the de Broglie-Bohm theory
No full textThere are three possible interpretations of the wave function in the de Broglie-Bohm theory: taking the wave function as corresponding to a physical entity or a property of the Bohmian particles or a law. In this paper, we argue that the first interpretation is favored by an analysis of protective measurements
Histoire de France sous le regne de Louïs XIV
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Quantal Time Asymmetry: Mathematical Foundation And Physical Interpretation
No full textTime in standard quantum mechanics extends from -infinity < t < + infinity; this is the result of a mathematical theorem (Stone-von Neumann) for the solutions of the Schrodinger equation for states or of the Heisenberg equation for observables. In reality t does not extend to t -> -infinity since according to causality, a quantum state phi(+) must be prepared first at a particular time t = t(0), before the probability vertical bar(psi(-)(t),phi+(t(0))vertical bar(2) for an observable psi(-) can be measured in it at t > t(0) (Feynman (1948)). In experiments on single Ba(+) ions, Dehmelt and others observed this finite preparation time as the ensemble of onset-times t(0)(1),t(0)(2), ..., t(0)(n) of dark periods. How the semigroup time evolution, t(0) equivalent to 0 < t < infinity with a beginning of time t(0), can suggest the parametrization of the resonance pole position of the Z-boson at S= s(R) as s(R) = (M(R) - i Gamma(R)/2)(2) in terms of a mass M(R) and a width Gamma(R) given by a lifetime tau = (h) over bar/Gamma(R), is the subject of this contribution dedicated to Augusto Garcia.Physic
Vacuum polarisation around an Aharonov-Bohm solenoid
No full textThe quantisation of a charged scalar field in an externally specified electromagnetic field, described by the vector potential Ai = ∂iƒ with ƒ(t,r,θ,z)=Bθ is discussed. The electromagnetic field is zero everywhere except at the origin; a singular magnetic field (Aharonov-Bohm field) exists at the origin. The vacuum polarization around such a magnetic field is computed and the non-local behaviour is discussed
Observation of Aharonov-Bohm conductance oscillations in a graphene ring
No full textWe investigate experimentally transport through ring-shaped devices etched in graphene and observe clear Aharonov-Bohm conductance oscillations. The temperature dependence of the oscillation amplitude indicates that below 1 K, the phase coherence length is comparable to or larger than the size of the ring. An increase in the amplitude is observed at high magnetic field, when the cyclotron diameter becomes comparable to the width of the arms of the ring. By measuring the dependence on gate voltage, we find that the Aharonov-Bohm effect vanishes at the charge neutrality point, and we observe an unexpected linear dependence of the oscillation amplitude on the ring conductance.Kavli Institute of NanoscienceApplied Science
Holism and Structuralism in U(1) Gauge Theory
No full textAfter decades of neglect philosophers of physics have discovered gauge theories--arguably the paradigm of modern field physics--as a genuine topic for foundational and philosophical research. Incidentally, in the last couple of years interest from the philosophy of physics in structural realism--in the eyes of its proponents the best suited realist position towards modern physics--has also raised. This paper tries to connect both topics and aims to show that structural realism gains further credence from an ontological analysis of gauge theories--in particular U(1) gauge theory. In the first part of the paper the framework of fiber bundle gauge theories is briefly presented and the interpretation of local gauge symmetry will be examined. In the second part, an ontological underdetermination of gauge theories is carved out by considering the various kinds of non-locality involved in such typical effects as the Aharonov-Bohm effect. The analysis shows that the peculiar form of non-separability figuring in gauge theories is a variant of spatiotemporal holism and can be distinguished from quantum theoretic holism. In the last part of the paper the arguments for a gauge theoretic support of structural realism are laid out and discussed
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