15,683 research outputs found
Quantumness beyond quantum mechanics
Bohmian mechanics allows us to understand quantum systems in the light of
other quantum traits than the well-known ones (coherence, diffraction,
interference, tunneling, discreteness, entanglement, etc.). Here the discussion
focusses precisely on two of these interesting aspects, which arise when
quantum mechanics is though within this theoretical framework: the non-crossing
property, which allows for distinguishability without erasing interference
patterns, and the possibility to define quantum probability tubes, along which
the probability remains constant all the way. Furthermore, taking into account
this hydrodynamic-like description as a link, it is also shown how this
knowledge (concepts and ideas) can be straightforwardly transferred to other
fields of physics (for example, the transmission of light along waveguides).Comment: 11 pages, 4 figures; based on a talk at the Conference "Emergent
Quantum Mechanics" / 5th Heinz von Foerster Congress (Vienna, Nov 11-13,
2011
Description of classical and quantum interference in view of the concept of flow line
Bohmian mechanics, a hydrodynamic formulation of quantum mechanics, relies on
the concept of trajectory, which evolves in time in compliance with dynamical
information conveyed by the wave function. Here this appealing idea is
considered to analyze both classical and quantum interference, thus providing
an alternative and more intuitive framework to understand the time-evolution of
waves, either in terms of the flow of energy (for mechanical waves, sound
waves, electromagnetic waves, for instance) or, analogously, the flow of
probability (quantum waves), respectively. Furthermore, this procedure also
supplies a more robust explanation of interference phenomena, which currently
is only based on the superposition principle. That is, while this principle
only describes how different waves combine and what effects these combinations
may lead to, flow lines provide a more precise explanation on how the energy or
probability propagate in space before, during and after the combination of such
waves, without dealing with them separately (i.e., the combination or
superposition is taken as a whole). In this sense, concepts such as
constructive and destructive interference, typically associated with the
superposition principle, physically correspond to more or less dense swarms of
(energy or probability) flow lines, respectively. A direct consequence of this
description is that, when considering the distribution of electromagnetic
energy flow lines behind two slits, each one covered by a differently oriented
polarizer, it is naturally found that external observers' information on the
slit crossed by single photons (understood as energy parcels) is totally
irrelevant for the existence of interference fringes, in striking contrast with
what is commonly stated and taught.Comment: 15 pages, 3 figure
Full quantum mechanical analysis of atomic three-grating Mach-Zehnder interferometry
Atomic three-grating Mach-Zehnder interferometry constitutes an important
tool to probe fundamental aspects of the quantum theory. There is, however, a
remarkable gap in the literature between the oversimplified models and robust
numerical simulations considered to describe the corresponding experiments.
Consequently, the former usually lead to paradoxical scenarios, such as the
wave-particle dual behavior of atoms, while the latter make difficult the data
analysis in simple terms. Here these issues are tackled by means of a simple
grating working model consisting of evenly-spaced Gaussian slits. As is shown,
this model suffices to explore and explain such experiments both analytically
and numerically, giving a good account of the full atomic journey inside the
interferometer, and hence contributing to make less mystic the physics
involved. More specifically, it provides a clear and unambiguous picture of the
wavefront splitting that takes place inside the interferometer, illustrating
how the momentum along each emerging diffraction order is well defined even
though the wave function itself still displays a rather complex shape. To this
end, the local transverse momentum is also introduced in this context as a
reliable analytical tool. The splitting, apart from being a key issue to
understand atomic Mach-Zehnder interferometry, also demonstrates at a
fundamental level how wave and particle aspects are always present in the
experiment, without incurring in any contradiction or interpretive paradox. On
the other hand, at a practical level, the generality and versatility of the
model and methodology presented, makes them suitable to attack analogous
problems in a simple manner after a convenient tuning.Comment: 17 pages, 6 figures (remarkably improved version
Averaged Singular Integral Estimation as a Bias Reduction Technique
This paper proposes an averaged version of singular integral estimators, whose bias achieves higher rates of convergence under smoothing assumptions. We derive exact bias bounds, without imposing smoothing assumptions, which are a basis for deriving the rates of convergence under differentiability assumptions.Publicad
Zeno dynamics in wave-packet diffraction spreading
We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno,
and inverse-Zeno effects in the observation of wave-packet spreading caused by
free evolution. The scheme is valid both in spatial diffraction of classical
optical waves and in time diffraction of a quantum wave packet. In the optical
realization, diffraction spreading is observed by placing slits between a light
source and a light-power detector. We show that the occurrence of Zeno or
anti-Zeno effects depends just on the frequency of observations between the
source and detector. These effects are seen to be related to the diffraction
mode theory in Fabry-Perot resonators.Comment: 7 pages, 8 figure
Evolution of the wave function of an atom hit by a photon in a three-grating interferometer
In 1995, Chapman et al. (1995 Phys. Rev. Lett. 75 2783) showed experimentally
that the interference contrast in a three-grating atom interferometer does not
vanish under the presence of scattering events with photons, as required by the
complementarity principle. In this work we provide an analytical study of this
experiment, determining the evolution of the atom wave function along the
three-grating Mach-Zehnder interferometer under the assumption that the atom is
hit by a photon after passing through the first grating. The consideration of a
transverse wave function in momentum representation is essential in this study.
As is shown, the number of atoms transmitted through the third grating is given
by a simple periodic function of the lateral shift along this grating, both in
the absence and in the presence of photon scattering. Moreover, the relative
contrast (laser on/laser off) is shown to be a simple analytical function of
the ratio d_p/\lambda_i, where d_p is the distance between atomic paths at the
scattering locus and \lambda_i the scattered photon wavelength. We argue that
this dependence, being in agreement with experimental results, can be regarded
to show compatibility of the wave and corpuscle properties of atoms.Comment: 8 pages, 4 figure
On-chip quantum tomography of mechanical nano-scale oscillators with guided Rydberg atoms
Nano-mechanical oscillators as well as Rydberg-atomic waveguides hosted on
micro-fabricated chip surfaces hold promise to become pillars of future quantum
technologies. In a hybrid platform with both, we show that beams of Rydberg
atoms in waveguides can quantum-coherently interrogate and manipulate
nanomechanical elements, allowing full quantum state tomography. Central to the
tomography are quantum non-demolition measurements using the Rydberg atoms as
probes. Quantum coherent displacement of the oscillator is also made possible,
by driving the atoms with external fields while they interact with the
oscillator. We numerically demonstrate the feasibility of this fully integrated
on-chip control and read-out suite for quantum nano-mechanics, taking into
account noise and error sources.Comment: 11 pages, 5 figures, 1 tabl
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