372 research outputs found
Direct evaluation of pure graph state entanglement
We address the question of quantifying entanglement in pure graph states.
Evaluation of multipartite entanglement measures is extremely hard for most
pure quantum states. In this paper we demonstrate how solving one problem in
graph theory, namely the identification of maximum independent set, allows us
to evaluate three multipartite entanglement measures for pure graph states. We
construct the minimal linear decomposition into product states for a large
group of pure graph states, allowing us to evaluate the Schmidt measure.
Furthermore we show that computation of distance-like measures such as relative
entropy of entanglement and geometric measure becomes tractable for these
states by explicit construction of closest separable and closest product states
respectively. We show how these separable states can be described using
stabiliser formalism as well as PEPs-like construction. Finally we discuss the
way in which introducing noise to the system can optimally destroy
entanglement.Comment: 23 pages, 9 figure
Learning more with less: Conditional PGGAN-based data augmentation for brain metastases detection using highly-rough annotation on MR images
Accurate Computer-Assisted Diagnosis, associated with proper data wrangling,
can alleviate the risk of overlooking the diagnosis in a clinical environment.
Towards this, as a Data Augmentation (DA) technique, Generative Adversarial
Networks (GANs) can synthesize additional training data to handle the
small/fragmented medical imaging datasets collected from various scanners;
those images are realistic but completely different from the original ones,
filling the data lack in the real image distribution. However, we cannot easily
use them to locate disease areas, considering expert physicians' expensive
annotation cost. Therefore, this paper proposes Conditional Progressive Growing
of GANs (CPGGANs), incorporating highly-rough bounding box conditions
incrementally into PGGANs to place brain metastases at desired positions/sizes
on 256 X 256 Magnetic Resonance (MR) images, for Convolutional Neural
Network-based tumor detection; this first GAN-based medical DA using automatic
bounding box annotation improves the training robustness. The results show that
CPGGAN-based DA can boost 10% sensitivity in diagnosis with clinically
acceptable additional False Positives. Surprisingly, further tumor realism,
achieved with additional normal brain MR images for CPGGAN training, does not
contribute to detection performance, while even three physicians cannot
accurately distinguish them from the real ones in Visual Turing Test.Comment: 9 pages, 7 figures, accepted to CIKM 2019 (acceptance rate: 19%
Diagonal-unitary 2-designs and their implementations by quantum circuits
We study efficient generations of random diagonal-unitary matrices, an
ensemble of unitary matrices diagonal in a given basis with randomly
distributed phases for their eigenvalues. Despite the simple algebraic
structure, they cannot be achieved by quantum circuits composed of a few-qubit
diagonal gates. We introduce diagonal-unitary -designs and present two
quantum circuits that implement diagonal-unitary -designs with the
computational basis in -qubit systems. One is composed of single-qubit
diagonal gates and controlled-phase gates with randomized phases, which
achieves an exact diagonal-unitary -design after applying the gates on all
pairs of qubits. The number of required gates is . If the
controlled-Z gates are used instead of the controlled-phase gates, the circuit
cannot achieve an exact -design, but achieves an -approximate
-design by applying gates on randomly selected pairs of qubits. Due to the
random choice of pairs, the circuit obtains extra randomness and the required
number of gates is at most . We also provide an
application of the circuits, a protocol of generating an exact -design of
random states by combining the circuits with a simple classical procedure
requiring random classical bits.Comment: Revised, 22 pages + Appendix, 3 figures; major revision from v2;
presentation is improved in v4; v5 is a published versio
On quantum teleportation with beam-splitter-generated entanglement
Following the lead of Cochrane, Milburn, and Munro [Phys. Rev. A {\bf 62},
062307 (2000)], we investigate theoretically quantum teleportation by means of
the number-sum and phase-difference variables. We study Fock-state entanglement
generated by a beam splitter and show that two-mode Fock-state inputs can be
entangled by a beam splitter into close approximations of maximally entangled
eigenstates of the phase difference and the photon-number sum
(Einstein-Podolsky-Rosen -- EPR -- states). Such states could be experimentally
feasible with on-demand single-photon sources. We show that the teleportation
fidelity can reach near unity when such ``quasi-EPR'' states are used as the
quantum channel.Comment: 7 pages (two-column), 7 figures, submitted to Phys. Rev. A. Text
unmodified, postscript error correcte
Entangled state preparation via dissipation-assisted adiabatic passages
The main obstacle for coherent control of open quantum systems is decoherence
due to different dissipation channels and the inability to precisely control
experimental parameters. To overcome these problems we propose to use
dissipation-assisted adiabatic passages. These are relatively fast processes
where the presence of spontaneous decay rates corrects for errors due to
non-adiabaticity while the system remains in a decoherence-free state and
behaves as predicted for an adiabatic passage. As a concrete example we present
a scheme to entangle atoms by moving them in and out of an optical cavity.Comment: 11 pages, 7 figures, minor changes, accepted for publication in Phys.
Rev.
Generation of maximum spin entanglement induced by cavity field in quantum-dot systems
Equivalent-neighbor interactions of the conduction-band electron spins of
quantum dots in the model of Imamoglu et al. [Phys. Rev. Lett. 83, 4204 (1999)]
are analyzed. Analytical solution and its Schmidt decomposition are found and
applied to evaluate how much the initially excited dots can be entangled to the
remaining dots if all of them are initially disentangled. It is demonstrated
that the perfect maximally entangled states (MES) can only be generated in the
systems of up to 6 dots with a single dot initially excited. It is also shown
that highly entangled states, approximating the MES with a good accuracy, can
still be generated in systems of odd number of dots with almost half of them
being excited. A sudden decrease of entanglement is observed by increasing the
total number of dots in a system with a fixed number of excitations.Comment: 6 pages, 7 figures, to appear in Phys. Rev.
Engineering arbitrary motional ionic state through realistic intensity-fluctuating laser pulses
We present a reliable scheme for engineering arbitrary motional ionic states
through an adaptation of the projection synthesis technique for trapped-ion
phenomena. Starting from a prepared coherent motional state, the Wigner
function of the desired state is thus sculpted from a Gaussian distribution.
The engineering process has also been developed to take into account the errors
arising from intensity fluctuations in the exciting-laser pulses required for
manipulating the electronic and vibrational states of the trapped ion. To this
end, a recently developed phenomenological-operator approach that allows for
the influence of noise will be applied. This approach furnishes a
straightforward technique to estimate the fidelity of the prepared state in the
presence of errors, precluding the usual extensive ab initio calculations. The
results obtained here by the phenomenological approach, to account for the
effects of noise in our engineering scheme, can be directly applied to any
other process involving trapped-ion phenomena.Comment: more information at http://www.df.ufscar.br/~quantum
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