1,828 research outputs found
Polarization-Entangled Light Pulses of 10^5 Photons
We experimentally demonstrate polarization entanglement for squeezed vacuum
pulses containing more than 10^5 photons. We also study photon-number
entanglement by calculating the Schmidt number and measuring its operational
counterpart. Theoretically, our pulses are the more entangled the brighter they
are. This promises important applications in quantum technologies, especially
photonic quantum gates and quantum memories.Comment: 8 pages, 6 figure
Verifying continuous variable entanglement of intense light pulses
Three different methods have been discussed to verify continuous variable
entanglement of intense light beams. We demonstrate all three methods using the
same set--up to facilitate the comparison. The non--linearity used to generate
entanglement is the Kerr--effect in optical fibres. Due to the brightness of
the entangled pulses, standard homodyne detection is not an appropriate tool
for the verification. However, we show that by using large asymmetric
interferometers on each beam individually, two non-commuting variables can be
accessed and the presence of entanglement verified via joint measurements on
the two beams. Alternatively, we witness entanglement by combining the two
beams on a beam splitter that yields certain linear combinations of quadrature
amplitudes which suffice to prove the presence of entanglement.Comment: 11 pages, 7 figures, to appear in Phys. Rev.
Preparing the bound instance of quantum entanglement
Among the possibly most intriguing aspects of quantum entanglement is that it
comes in "free" and "bound" instances. Bound entangled states require entangled
states in preparation but, once realized, no free entanglement and therefore no
pure maximally entangled pairs can be regained. Their existence hence certifies
an intrinsic irreversibility of entanglement in nature and suggests a
connection with thermodynamics. In this work, we present a first experimental
unconditional preparation and detection of a bound entangled state of light. We
consider continuous-variable entanglement, use convex optimization to identify
regimes rendering its bound character well certifiable, and realize an
experiment that continuously produced a distributed bound entangled state with
an extraordinary and unprecedented significance of more than ten standard
deviations away from both separability and distillability. Our results show
that the approach chosen allows for the efficient and precise preparation of
multimode entangled states of light with various applications in quantum
information, quantum state engineering and high precision metrology.Comment: The final version accounts for a recent comment in Nature Physics
[24] clarifying that a previous claim of having generated bound entanglement
[23] was not supported by the authors' data. We also extended our
introduction and discussion and also added reference
An Unsupervised Method for Estimating Class Separability of Datasets with Application to LLMs Fine-Tuning
This paper proposes an unsupervised method that leverages topological
characteristics of data manifolds to estimate class separability of the data
without requiring labels. Experiments conducted in this paper on several
datasets demonstrate a clear correlation and consistency between the class
separability estimated by the proposed method with supervised metrics like
Fisher Discriminant Ratio~(FDR) and cross-validation of a classifier, which
both require labels. This can enable implementing learning paradigms aimed at
learning from both labeled and unlabeled data, like semi-supervised and
transductive learning. This would be particularly useful when we have limited
labeled data and a relatively large unlabeled dataset that can be used to
enhance the learning process. The proposed method is implemented for language
model fine-tuning with automated stopping criterion by monitoring class
separability of the embedding-space manifold in an unsupervised setting. The
proposed methodology has been first validated on synthetic data, where the
results show a clear consistency between class separability estimated by the
proposed method and class separability computed by FDR. The method has been
also implemented on both public and internal data. The results show that the
proposed method can effectively aid -- without the need for labels -- a
decision on when to stop or continue the fine-tuning of a language model and
which fine-tuning iteration is expected to achieve a maximum classification
performance through quantification of the class separability of the embedding
manifold
Quantum states with a positive partial transpose are useful for metrology
We show that multipartite quantum states that have a positive partial
transpose with respect to all bipartitions of the particles can outperform
separable states in linear interferometers. We introduce a powerful iterative
method to find such states. We present some examples for multipartite states
and examine the scaling of the precision with the particle number. Some
bipartite examples are also shown that possess an entanglement very robust to
noise. We also discuss the relation of metrological usefulness to Bell
inequality violation. We find that quantum states that do not violate any Bell
inequality can outperform separable states metrologically. We present such
states with a positive partial transpose, as well as with a non-positive
positive partial transpose.Comment: 6 pages including two figures + three-page supplement including two
figures using revtex 4.1, with numerically obtained density matrices as text
files; v2: published version; v3: published version, typo in the 4x4 bound
entangled state is corrected (noticed by Peng Yin
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