241 research outputs found
Weakly supervised 3D Reconstruction with Adversarial Constraint
Supervised 3D reconstruction has witnessed a significant progress through the
use of deep neural networks. However, this increase in performance requires
large scale annotations of 2D/3D data. In this paper, we explore inexpensive 2D
supervision as an alternative for expensive 3D CAD annotation. Specifically, we
use foreground masks as weak supervision through a raytrace pooling layer that
enables perspective projection and backpropagation. Additionally, since the 3D
reconstruction from masks is an ill posed problem, we propose to constrain the
3D reconstruction to the manifold of unlabeled realistic 3D shapes that match
mask observations. We demonstrate that learning a log-barrier solution to this
constrained optimization problem resembles the GAN objective, enabling the use
of existing tools for training GANs. We evaluate and analyze the manifold
constrained reconstruction on various datasets for single and multi-view
reconstruction of both synthetic and real images
Nonlinear interferometry with Bose-Einstein condensates
We analyze a proposed experiment [Boixo et al., Phys. Rev. Lett. 101, 040403 (2008)] for achieving sensitivity scaling better than 1/N in a nonlinear Ramsey interferometer that uses a two-mode Bose-Einstein condensate (BEC) of N atoms. We present numerical simulations that confirm the analytical predictions for the effect of the spreading of the BEC ground-state wave function on the ideal 1/N^(3/2) scaling. Numerical integration of the coupled, time-dependent, two-mode Gross-Pitaevskii equations allows us to study the several simplifying assumptions made in the initial analytic study of the proposal and to explore when they can be justified. In particular, we find that the two modes share the same spatial wave function for a length of time that is sufficient to run the metrology scheme
Interpreting quantum discord through quantum state merging
We present an operational interpretation of quantum discord based on the
quantum state merging protocol. Quantum discord is the markup in the cost of
quantum communication in the process of quantum state merging, if one discards
relevant prior information. Our interpretation has an intuitive explanation
based on the strong subadditivity of von Neumann entropy. We use our result to
provide operational interpretations of other quantities like the local purity
and quantum deficit. Finally, we discuss in brief some instances where our
interpretation is valid in the single copy scenario.Comment: 5 pages, no figures. See http://arxiv.org/abs/1008.3205 for similar
results. Typos fixed, references and acknowledgements updated. End note adde
Quantum metrology with Bose-Einstein condensates
We show how a generalized quantum metrology protocol can be implemented in a two-mode Bose-Einstein condensate of n atoms, achieving a sensitivity that scales better than 1/n and approaches 1/n^(3/2) for appropriate design of the condensate
Real-world Quantum Sensors: Evaluating Resources for Precision Measurement
Quantum physics holds the promise of enabling certain tasks with better
performance than possible when only classical resources are employed. The
quantum phenomena present in many experiments signify nonclassical behavior,
but do not always imply superior performance. Quantifying the enhancement
achieved from quantum behavior requires careful analysis of the resources
involved. We analyze the specific case of parameter estimation using an optical
interferometer, where increased precision can be achieved using quantum probe
states. Common performance measures are examined and it is shown that some
overestimate the improvement. For the simplest experimental case we compare the
different measures and show this overestimate explicitly. We give the preferred
analysis of real-world experiments and calculate benchmark values for
experimental parameters necessary to realize a precision enhancement.Comment: 8 pages, 3 figure
Quantum Discord and Quantum Computing - An Appraisal
We discuss models of computing that are beyond classical. The primary
motivation is to unearth the cause of nonclassical advantages in computation.
Completeness results from computational complexity theory lead to the
identification of very disparate problems, and offer a kaleidoscopic view into
the realm of quantum enhancements in computation. Emphasis is placed on the
`power of one qubit' model, and the boundary between quantum and classical
correlations as delineated by quantum discord. A recent result by Eastin on the
role of this boundary in the efficient classical simulation of quantum
computation is discussed. Perceived drawbacks in the interpretation of quantum
discord as a relevant certificate of quantum enhancements are addressed.Comment: To be published in the Special Issue of the International Journal of
Quantum Information on "Quantum Correlations: entanglement and beyond." 11
pages, 4 figure
Information transfer through a one-atom micromaser
We consider a realistic model for the one-atom micromaser consisting of a
cavity maintained in a steady state by the streaming of two-level Rydberg atoms
passing one at a time through it. We show that it is possible to monitor the
robust entanglement generated between two successive experimental atoms passing
through the cavity by the control decoherence parameters. We calculate the
entanglement of formation of the joint two-atom state as a function of the
micromaser pump parameter. We find that this is in direct correspondence with
the difference of the Shannon entropy of the cavity photons before and after
the passage of the atoms for a reasonable range of dissipation parameters. It
is thus possible to demonstrate information transfer between the cavity and the
atoms through this set-up.Comment: Revtex, 5 pages, 2 encapsulated ps figures; added discussion on
information transfer in relation with cavity photon statistics; typos
corrected; Accepted for Publicaiton in Europhysics Letter
Quantum-limited metrology and Bose-Einstein condensates
We discuss a quantum-metrology protocol designed to estimate a physical
parameter in a Bose-Einstein condensate of N atoms, and we show that the
measurement uncertainty can decrease faster than 1/N. The 1/N scaling is
usually thought to be the best possible in any measurement scheme. From the
perspective of quantum information theory, we outline the main idea that leads
to a measurement uncertainty that scales better than 1/N. We examine in detail
some potential problems and challenges that arise in implementing such a
measurement protocol using a Bose-Einstein condensate. We discuss how some of
these issues can be dealt with by using lower-dimensional condensates trapped
in nonharmonic potentials.Comment: 32 pages, 1 figure, updated reference
Quantifying the Nonclassicality of Operations
Deep insight can be gained into the nature of nonclassical correlations by
studying the quantum operations that create them. Motivated by this we propose
a measure of nonclassicality of a quantum operation utilizing the relative
entropy to quantify its commutativity with the completely dephasing operation.
We show that our measure of nonclassicality is a sum of two independent
contributions, the generating power -- its ability to produce nonclassical
states out of classical ones, and the distinguishing power -- its usefulness to
a classical observer for distinguishing between classical and nonclassical
states. Each of these effects can be exploited individually in quantum
protocols. We further show that our measure leads to an interpretation of
quantum discord as the difference in superdense coding capacities between a
quantum state and the best classical state when both are produced at a source
that makes a classical error during transmission.Comment: Published version, 5 pages, 3 figures plus 4 pages of Supplementary
Materia
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