1,045 research outputs found
Evolution speed of open quantum dynamics
The space of density matrices is embedded in a Euclidean space to deduce the
dynamical equation satisfied by the state of an open quantum system. The
Euclidean norm is used to obtain an explicit expression for the speed of the
evolution of the state. The unitary contribution to the evolution speed is
given by the modified skew information of the Hamiltonian, while the radial
component of the evolution speed, connected to the rate at which the purity of
the state changes, is shown to be determined by the modified skew information
of the Lindblad operators. An open-system analogue of the quantum navigation
problem is posed, and a perturbative analysis is presented to identify the
amount of change on the speed. Properties of the evolution speed are examined
further through example systems, showing that the evolution speed need not be a
decreasing function of time.Comment: 5 page
Sample Size Estimation using the Receiver Operating Characteristic Curve
In this paper we describe two related approaches to estimating the sample sizes required to statistically compare the performance of two classifiers: acceptable failure rates (AFR) and the area under the receiver operating characteristic (ROC) curve (AUC). In particular, we consider rare event detection problems, where the prior class probabilities are highly skewed, and measure performance at a specific operating point and for the whole ROC curve. It is shown that the use of AUC as a performance measure is preferable to AFR as it requires a smaller data set to demonstrate superiority of one classifier over another
Bosonic autonomous entanglement engines with weak bath coupling are impossible
Entanglement is a fundamental feature of quantum physics and a key resource
for quantum communication, computing and sensing. Entangled states are fragile
and maintaining coherence is a central challenge in quantum information
processing. Nevertheless, entanglement can be generated and stabilised through
dissipative processes. In fact, entanglement has been shown to exist in the
steady state of certain interacting quantum systems subject solely to
incoherent coupling to thermal baths. This has been demonstrated in a range of
bi- and multipartite settings using systems of finite dimension. Here we focus
on the steady state of infinite-dimensionsional bosonic systems. Specifically,
we consider any set of bosonic modes undergoing excitation-number-preserving
interactions of arbitrary strength and divided between an arbitrary number of
parties that each couple weakly to thermal baths at different temperatures. We
show that the steady state is always separable.Comment: 10 pages, 1 figur
Persistent nonlocality in an ultracold-atom environment
We investigate nonlocal quantum correlations arising between multiple two-level impurity atoms coupled to an ultracold bosonic gas. We find that the environment-induced dynamics of the impurity subsystem can generate nonlocal states that are robust against noise and violate a multipartite Bell inequality when projective spin measurements are made. Genuine multipartite nonlocality is also observed in a system of three impurities. We show that non-Markovian effects, and the persistence of coherences in the impurity subsystem, are crucial for preventing complete loss of nonlocality and allow for nonlocal correlations to be generated and maintained for extended periods of time
Steering-based randomness certification with squeezed states and homodyne measurements
We present a scheme for quantum randomness certification based on quantum
steering. The protocol is one-sided device independent, providing high
security, but requires only states and measurements that are simple to realise
on quantum optics platforms - entangled squeezed vacuum states and homodyne
detection. This ease of implementation is demonstrated by certifying randomness
in existing experimental data and implies that giga-hertz random bit rates
should be attainable with current technology. Furthermore, the steering-based
setting represents the closest to full device independence that can be achieved
using purely Gaussian states and measurements.Comment: 8 pages, 6 figure
SOX, corporate transparency, and the cost of debt
We investigate the impact of the SarbanesâOxley (SOX) Act on the cost of debt through its effect on the reliability of financial reporting. Using Credit Default Swap (CDS) spreads and a structural CDS pricing model, we calibrate a firm-level corporate opacity parameter in the pre- and post-SOX periods. Our analysis shows that corporate opacity and the cost of debt decrease significantly after SOX. The median firm in our sample experiences an 18bp reduction on its five-year CDS spread as a result of lower opacity following SOX, amounting to total annual savings of $ 844million for the 252 firms in our sample. Furthermore, the reduction in opacity tends to be larger for firms that in the pre-SOX period have lower accrual quality, less conservative earnings, lower number of independent directors, lower S& P Transparency and Disclosure ratings, and are more likely to benefit from SOX-compliance according to Chhaochharia and Grinsteinâs (2007) criteria
Search for CP Violation in D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) Decays
A search for charge-parity () violation in Cabibbo-suppressed , and decays is reported
using proton-proton collision data, corresponding to an integrated luminosity
of 3.8 fb, collected at a center-of-mass energy of 13 TeV with the LHCb
detector. High-yield samples of kinematically and topologically similar
Cabibbo-favored decays are analyzed to subtract nuisance
asymmetries due to production and detection effects, including those induced by
violation in the neutral kaon system. The results are \begin{align*}
\mathcal{A}_{CP}(D_s^+\to K_S^0 \pi^+)
&=\left(\phantom{-}1.3\phantom{0}\pm1.9\phantom{0}\pm0.5\phantom{0}\right)\times10^{-3},\\
\mathcal{A}_{CP}(D^+\to K_S^0 K^+)
&=\left(-0.09\pm0.65\pm0.48\right)\times10^{-3},\\ \mathcal{A}_{CP}(D^+\to \phi
\pi^+) &=\left(\phantom{-}0.05\pm0.42\pm0.29\right)\times10^{-3}, \end{align*}
where the first uncertainties are statistical and the second systematic. They
are the most precise measurements of these quantities to date, and are
consistent with symmetry.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-002.htm
Observation of the doubly charmed baryon decay Îcc++âÎcâČ+Ï+
The Îcc++âÎcâČ+Ï+ decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fbâ1. The Îcc++âÎcâČ+Ï+ decay is reconstructed partially, where the photon from the ÎcâČ+âÎc+Îł decay is not reconstructed and the pKâÏ+ final state of the Îc+ baryon is employed. The Îcc++âÎcâČ+Ï+branching fraction relative to that of the Îcc++âÎc+Ï+ decay is measured to be 1.41 ± 0.17 ± 0.10, where the first uncertainty is statistical and the second systematic. [Figure not available: see fulltext.
Test of lepton universality in decays
The first simultaneous test of muon-electron universality using
and decays is performed, in two ranges of the dilepton
invariant-mass squared, . The analysis uses beauty mesons produced in
proton-proton collisions collected with the LHCb detector between 2011 and
2018, corresponding to an integrated luminosity of 9 . Each
of the four lepton universality measurements reported is either the first in
the given interval or supersedes previous LHCb measurements. The
results are compatible with the predictions of the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-046.html (LHCb
public pages
Study of charmonium and charmonium-like contributions in B+ â J/ÏηK+ decays
A study of B+â J/ÏηK+ decays, followed by J/Ï â ÎŒ+ÎŒâ and η â γγ, is performed using a dataset collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fbâ1. The J/Ïη mass spectrum is investigated for contributions from charmonia and charmonium-like states. Evidence is found for the B+â (Ï2(3823) â J/Ïη)K+ and B+â (Ï(4040) â J/Ïη)K+ decays with significance of 3.4 and 4.7 standard deviations, respectively. This constitutes the first evidence for the Ï2(3823) â J/Ïη decay
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