46 research outputs found
Channel Capacities versus Entanglement Measures in Multiparty Quantum States
For quantum states of two subsystems, entanglement measures are related to
capacities of communication tasks -- highly entangled states give higher
capacity of transmitting classical as well as quantum information. However, we
show that this is no more the case in general: quantum capacities of
multi-access channels, motivated by communication in quantum networks, do not
have any relation with genuine multiparty entanglement measures. Along with
revealing the structural richness of multi-access channel capacities, this
gives us a tool to classify multiparty quantum states from the perspective of
its usefulness in quantum networks, which cannot be visualized by known
multiparty entanglement measures.Comment: 6 pages, 2 figures, RevTeX4; v2: minor changes, some implications
strengthene
Concentration of Physician Services Across Insurers and Effects on Quality: Early Evidence From Medicare Advantage.
BackgroundA growing proportion of Medicare beneficiaries is covered by private insurers through Medicare Advantage, yet little is known about how these plans are structured in terms of relationships with physicians and implications for quality of care.ObjectiveThe objective of this study was to assess whether greater physician concentration of services across insurers was associated with higher quality in Medicare Advantage (MA), overall and particularly among MA insurers serving a high proportion of vulnerable enrollees.Research designA retrospective cohort design with regression analysis.Data sourcesThe primary dataset was 2014 MA encounter records submitted by insurers to the Centers for Medicare and Medicaid Services, covering 600,329 physicians across 119 insurers. These data were merged with Centers for Medicare and Medicaid Services data on MA contract quality rating as well as physician characteristics in the Medicare Data on Provider Practice and Specialty file.MeasuresTwo measures were generated to capture the concentration of physician services across insurers: the percentage of a physician's Medicare services which was through MA (MA penetration); and the percentage of a physician's MA services with a specific insurer (insurer share of MA services).ResultsGreater MA penetration and insurer share of MA services were each associated with higher MA plan quality. The relationship between insurer share and quality was stronger in contracts with a relatively high percentage of disabled enrollees.ConclusionGreater physician concentration of services across MA insurers was associated with a higher quality of care overall and especially among vulnerable enrollees
Locally accessible information: How much can the parties gain by cooperating?
We investigate measurements of bipartite ensembles restricted to local
operations and classical communication and find a universal Holevo-like upper
bound on the locally accessible information. We analyze our bound and exhibit a
class of states which saturate it. Finally, we link the bound to the problem of
quantification of the nonlocality of the operations necessary to extract
locally unaccessible information.Comment: 4 pages, no figures, RevTeX4; v2: a conjecture partially proven,
results unchanged; v3: small changes in presentation, published versio
Testing Quantum Dynamics using Signaling
We consider a physical system in which the description of states and
measurements follow the usual quantum mechanical rules. We also assume that the
dynamics is linear, but may not be fully quantum (i.e unitary). We show that in
such a physical system, certain complementary evolutions, namely cloning and
deleting operations that give a better fidelity than quantum mechanically
allowed ones, in one (inaccessible) region, lead to signaling to a far-apart
(accessible) region. To show such signaling, one requires certain two-party
quantum correlated states shared between the two regions. Subsequent
measurements are performed only in the accessible part to detect such
phenomenon.Comment: 4 pages, 2 figures, RevTeX4; v2: published versio
Genuine Multiparty Quantum Entanglement Suppresses Multiport Classical Information Transmission
We establish a universal complementarity relation between the capacity of
classical information transmission by employing a multiparty quantum state as a
multiport quantum channel, and the genuine multipartite entanglement of the
quantum state. The classical information transfer is from a sender to several
receivers by using the quantum dense coding protocol with the multiparty
quantum state shared between the sender and the receivers. The relation holds
for arbitrary pure or mixed quantum states of an arbitrary number of parties in
arbitrary dimensions.Comment: 5 (+ epsilon) pages, 2 figures, Revtex4-1; v2: Theorem 3 extended to
all states, other results unchange
Capacities of Quantum Channels for Massive Bosons and Fermions
We consider the capacity of classical information transfer for noiseless
quantum channels carrying a finite average number of massive bosons and
fermions. The maximum capacity is attained by transferring the Fock states
generated from the grand-canonical ensemble. Interestingly, the channel
capacity for a Bose gas indicates the onset of a Bose-Einstein condensation, by
changing its qualitative behavior at the criticality, while for a channel
carrying weakly attractive fermions, it exhibits the signatures of
Bardeen-Cooper-Schrieffer transition. We also show that for noninteracting
particles, fermions are better carriers of information than bosons.Comment: 4 pages, 3 eps figures, RevTeX4; v2: discussions added, small
changes, published versio
Locally Accessible Information of Multisite Quantum Ensembles Violates Monogamy
Locally accessible information is a useful information-theoretic physical
quantity of an ensemble of multiparty quantum states. We find it has properties
akin to quantum as well as classical correlations of single multiparty quantum
states. It satisfies monotonicity under local quantum operations and classical
communication. However we show that it does not follow monogamy, an important
property usually satisfied by quantum correlations, and actually violates any
such relation to the maximal extent. Violation is obtained even for locally
indistinguishable, but globally orthogonal, multisite ensembles. The results
assert that while single multiparty quantum states are monogamous with respect
to their shared quantum correlations, ensembles of multiparty quantum states
may not be so. The results have potential implications for quantum
communication systems.Comment: 6 pages, RevTeX
Error-Resistant Distributed Quantum Computation in Trapped Ion Chain
We consider experimentally feasible chains of trapped ions with pseudo-spin
1/2, and find models that can potentially be used to implement error-resistant
quantum computation. Similar in spirit to classical neural networks, the
error-resistance of the system is achieved by encoding the qubits distributed
over the whole system. We therefore call our system a ''quantum neural
network'', and present a ''quantum neural network model of quantum
computation''. Qubits are encoded in a few quasi-degenerated low energy levels
of the whole system, separated by a large gap from the excited states, and
large energy barriers between themselves. We investigate protocols for
implementing a universal set of quantum logic gates in the system, by adiabatic
passage of a few low-lying energy levels of the whole system. Naturally
appearing and potentially dangerous distributed noise in the system leaves the
fidelity of the computation virtually unchanged, if it is not too strong. The
computation is also naturally resilient to local perturbations of the spins.Comment: 10 pages, 7 figures, RevTeX4; v2: another noise model analysed,
published versio
Do Financial Incentives Reduce Intrinsic Motivation for Weight Loss? Evidence from Two Tests of Crowding Out
Financial incentives have been used successfully to promote health behaviors, however they may be counterproductive if they crowd out pre-existing intrinsic motivation and lead to a decrease in performance once incentives are removed to a level lower than they had never been introduced. We provide new evidence that incentives do not crowd out intrinsic motivation in the case of weight loss. We measure motivation via a survey administered before and after the introduction of financial incentives in two weight loss field experiments and find no evidence that intrinsic motivation fell among participants receiving incentives compared to control participants who do not receive incentives