331 research outputs found
Adaptive experimental design for one-qubit state estimation with finite data based on a statistical update criterion
We consider 1-qubit mixed quantum state estimation by adaptively updating
measurements according to previously obtained outcomes and measurement
settings. Updates are determined by the average-variance-optimality
(A-optimality) criterion, known in the classical theory of experimental design
and applied here to quantum state estimation. In general, A-optimization is a
nonlinear minimization problem; however, we find an analytic solution for
1-qubit state estimation using projective measurements, reducing computational
effort. We compare numerically two adaptive and two nonadaptive schemes for
finite data sets and show that the A-optimality criterion gives more precise
estimates than standard quantum tomography.Comment: 15 pages, 7 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%
Quantum cobwebs: Universal entangling of quantum states
Entangling an unknown qubit with one type of reference state is generally
impossible. However, entangling an unknown qubit with two types of reference
states is possible. To achieve this, we introduce a new class of states called
zero sum amplitude (ZSA) multipartite, pure entangled states for qubits and
study their salient features. Using shared-ZSA state, local operation and
classical communication we give a protocol for creating multipartite entangled
states of an unknown quantum state with two types of reference states at remote
places. This provides a way of encoding an unknown pure qubit state into a
multiqubit entangled state. We quantify the amount of classical and quantum
resources required to create universal entangled states. This is possibly a
strongest form of quantum bit hiding with multiparties.Comment: Invited talk in II Winter Institute on FQTQO: Quantum Information
Processing, held at S. N. Bose Center for Basic Science, Kolkata, during Jan
2-11, 2002. (To appear in Pramana-J. of Physics, 2002.
Decoherence in nonclassical motional states of a trapped ion
Published versio
Mixedness and teleportation
We show that on exceeding a certain degree of mixedness (as quantified by the
von Neumann entropy), entangled states become useless for teleporatation. By
increasing the dimension of the entangled systems, this entropy threshold can
be made arbitrarily close to maximal. This entropy is found to exceed the
entropy threshold sufficient to ensure the failure of dense coding.Comment: 6 pages, no figure
Quantum Cloning Machines of a d-level System
The optimal N to M () quantum cloning machines for the d-level system
are presented. The unitary cloning transformations achieve the bound of the
fidelity.Comment: Revtex, 4 page
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
Classification of multipartite entangled states by multidimensional determinants
We find that multidimensional determinants "hyperdeterminants", related to
entanglement measures (the so-called concurrence or 3-tangle for the 2 or 3
qubits, respectively), are derived from a duality between entangled states and
separable states. By means of the hyperdeterminant and its singularities, the
single copy of multipartite pure entangled states is classified into an onion
structure of every closed subset, similar to that by the local rank in the
bipartite case. This reveals how inequivalent multipartite entangled classes
are partially ordered under local actions. In particular, the generic entangled
class of the maximal dimension, distinguished as the nonzero hyperdeterminant,
does not include the maximally entangled states in Bell's inequalities in
general (e.g., in the qubits), contrary to the widely known
bipartite or 3-qubit cases. It suggests that not only are they never locally
interconvertible with the majority of multipartite entangled states, but they
would have no grounds for the canonical n-partite entangled states. Our
classification is also useful for the mixed states.Comment: revtex4, 10 pages, 4 eps figures with psfrag; v2 title changed, 1
appendix added, to appear in Phys. Rev.
Four Photon Entanglement from Down Conversion
Double-pair emission from type-II parametric down conversion results in a
highly entangled 4-photon state. Due to interference, which is similar to
bunching from thermal emission, this state is not simply a product of two
pairs. The observation of this state can be achieved by splitting the two
emission modes at beam splitters and subsequent detection of a photon in each
output. Here we describe the features of this state and give a Bell theorem for
a 4-photon test of local realistic hidden variable theories.Comment: 5 pages, 1 figure, submitted to PR
Separability and distillability of multiparticle quantum systems
We present a family of 3--qubit states to which any arbitrary state can be
depolarized. We fully classify those states with respect to their separability
and distillability properties. This provides a sufficient condition for
nonseparability and distillability for arbitrary states. We generalize our
results to --particle states.Comment: replaced with published version (Phys.Rev.Lett.), in parts rewritten
and clarifie
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