34,744 research outputs found
The SLH framework for modeling quantum input-output networks
Many emerging quantum technologies demand precise engineering and control
over networks consisting of quantum mechanical degrees of freedom connected by
propagating electromagnetic fields, or quantum input-output networks. Here we
review recent progress in theory and experiment related to such quantum
input-output networks, with a focus on the SLH framework, a powerful modeling
framework for networked quantum systems that is naturally endowed with
properties such as modularity and hierarchy. We begin by explaining the
physical approximations required to represent any individual node of a network,
eg. atoms in cavity or a mechanical oscillator, and its coupling to quantum
fields by an operator triple . Then we explain how these nodes can be
composed into a network with arbitrary connectivity, including coherent
feedback channels, using algebraic rules, and how to derive the dynamics of
network components and output fields. The second part of the review discusses
several extensions to the basic SLH framework that expand its modeling
capabilities, and the prospects for modeling integrated implementations of
quantum input-output networks. In addition to summarizing major results and
recent literature, we discuss the potential applications and limitations of the
SLH framework and quantum input-output networks, with the intention of
providing context to a reader unfamiliar with the field.Comment: 60 pages, 14 figures. We are still interested in receiving
correction
Medical image enhancement using threshold decomposition driven adaptive morphological filter
One of the most common degradations in medical images is their poor contrast quality. This suggests the use of contrast enhancement methods as an attempt to modify the intensity distribution of the image. In this paper, a new edge detected morphological filter is proposed to sharpen digital medical images. This is done by detecting the positions of the edges and then applying a class of morphological filtering. Motivated by the success of threshold decomposition, gradientbased operators are used to detect the locations of the edges. A morphological filter is used to sharpen these detected edges. Experimental results demonstrate that the detected edge deblurring filter improved the visibility and perceptibility of various embedded structures in digital medical images. Moreover, the performance of the proposed filter is superior to that of other sharpener-type filters
Deterministic and cascadable conditional phase gate for photonic qubits
Previous analyses of conditional \phi-phase gates for photonic qubits that
treat cross-phase modulation (XPM) in a causal, multimode, quantum field
setting suggest that a large (~\pi rad) nonlinear phase shift is always
accompanied by fidelity-degrading noise [J. H. Shapiro, Phys. Rev. A 73, 062305
(2006); J. Gea-Banacloche, Phys. Rev. A 81, 043823 (2010)]. Using an atomic
V-system to model an XPM medium, we present a conditional phase gate that, for
sufficiently small nonzero \phi, has high fidelity. The gate is made cascadable
by using using a special measurement, principal mode projection, to exploit the
quantum Zeno effect and preclude the accumulation of fidelity-degrading
departures from the principal-mode Hilbert space when both control and target
photons illuminate the gate
Efficient Classical Simulation of Optical Quantum Circuits
We identify a broad class of physical processes in an optical quantum circuit
that can be efficiently simulated on a classical computer: this class includes
unitary transformations, amplification, noise, and measurements. This
simulatability result places powerful constraints on the capability to realize
exponential quantum speedups as well as on inducing an optical nonlinear
transformation via linear optics, photodetection-based measurement and
classical feedforward of measurement results, optimal cloning, and a wide range
of other processes.Comment: 4 pages, published versio
Regularized linearization for quantum nonlinear optical cavities: Application to Degenerate Optical Parametric Oscillators
Nonlinear optical cavities are crucial both in classical and quantum optics;
in particular, nowadays optical parametric oscillators are one of the most
versatile and tunable sources of coherent light, as well as the sources of the
highest quality quantum-correlated light in the continuous variable regime.
Being nonlinear systems, they can be driven through critical points in which a
solution ceases to exist in favour of a new one, and it is close to these
points where quantum correlations are the strongest. The simplest description
of such systems consists in writing the quantum fields as the classical part
plus some quantum fluctuations, linearizing then the dynamical equations with
respect to the latter; however, such an approach breaks down close to critical
points, where it provides unphysical predictions such as infinite photon
numbers. On the other hand, techniques going beyond the simple linear
description become too complicated especially regarding the evaluation of
two-time correlators, which are of major importance to compute observables
outside the cavity. In this article we provide a regularized linear description
of nonlinear cavities, that is, a linearization procedure yielding physical
results, taking the degenerate optical parametric oscillator as the guiding
example. The method, which we call self-consistent linearization, is shown to
be equivalent to a general Gaussian ansatz for the state of the system, and we
compare its predictions with those obtained with available exact (or
quasi-exact) methods.Comment: Comments and suggestions are welcom
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