290 research outputs found
A Two-Threshold Model for Scaling Laws of Non-Interacting Snow Avalanches
The sizes of snow slab failure that trigger snow avalanches are power-law
distributed. Such a power-law probability distribution function has also been
proposed to characterize different landslide types. In order to understand this
scaling for gravity driven systems, we introduce a two-threshold 2-d cellular
automaton, in which failure occurs irreversibly. Taking snow slab avalanches as
a model system, we find that the sizes of the largest avalanches just
preceeding the lattice system breakdown are power law distributed. By tuning
the maximum value of the ratio of the two failure thresholds our model
reproduces the range of power law exponents observed for land-, rock- or snow
avalanches. We suggest this control parameter represents the material cohesion
anisotropy.Comment: accepted PR
Tight bounds for classical and quantum coin flipping
Coin flipping is a cryptographic primitive for which strictly better
protocols exist if the players are not only allowed to exchange classical, but
also quantum messages. During the past few years, several results have appeared
which give a tight bound on the range of implementable unconditionally secure
coin flips, both in the classical as well as in the quantum setting and for
both weak as well as strong coin flipping. But the picture is still incomplete:
in the quantum setting, all results consider only protocols with perfect
correctness, and in the classical setting tight bounds for strong coin flipping
are still missing. We give a general definition of coin flipping which unifies
the notion of strong and weak coin flipping (it contains both of them as
special cases) and allows the honest players to abort with a certain
probability. We give tight bounds on the achievable range of parameters both in
the classical and in the quantum setting.Comment: 18 pages, 2 figures; v2: published versio
No extension of quantum theory can have improved predictive power
According to quantum theory, measurements generate random outcomes, in stark
contrast with classical mechanics. This raises the question of whether there
could exist an extension of the theory which removes this indeterminism, as
suspected by Einstein, Podolsky and Rosen (EPR). Although this has been shown
to be impossible, existing results do not imply that the current theory is
maximally informative. Here we ask the more general question of whether any
improved predictions can be achieved by any extension of quantum theory. Under
the assumption that measurements can be chosen freely, we answer this question
in the negative: no extension of quantum theory can give more information about
the outcomes of future measurements than quantum theory itself. Our result has
significance for the foundations of quantum mechanics, as well as applications
to tasks that exploit the inherent randomness in quantum theory, such as
quantum cryptography.Comment: 6 pages plus 7 of supplementary material, 3 figures. Title changed.
Added discussion on Bell's notion of locality. FAQ answered at
http://perimeterinstitute.ca/personal/rcolbeck/FAQ.htm
Causality - Complexity - Consistency: Can Space-Time Be Based on Logic and Computation?
The difficulty of explaining non-local correlations in a fixed causal
structure sheds new light on the old debate on whether space and time are to be
seen as fundamental. Refraining from assuming space-time as given a priori has
a number of consequences. First, the usual definitions of randomness depend on
a causal structure and turn meaningless. So motivated, we propose an intrinsic,
physically motivated measure for the randomness of a string of bits: its length
minus its normalized work value, a quantity we closely relate to its Kolmogorov
complexity (the length of the shortest program making a universal Turing
machine output this string). We test this alternative concept of randomness for
the example of non-local correlations, and we end up with a reasoning that
leads to similar conclusions as in, but is conceptually more direct than, the
probabilistic view since only the outcomes of measurements that can actually
all be carried out together are put into relation to each other. In the same
context-free spirit, we connect the logical reversibility of an evolution to
the second law of thermodynamics and the arrow of time. Refining this, we end
up with a speculation on the emergence of a space-time structure on bit strings
in terms of data-compressibility relations. Finally, we show that logical
consistency, by which we replace the abandoned causality, it strictly weaker a
constraint than the latter in the multi-party case.Comment: 17 pages, 16 figures, small correction
Random Numbers Certified by Bell's Theorem
Randomness is a fundamental feature in nature and a valuable resource for
applications ranging from cryptography and gambling to numerical simulation of
physical and biological systems. Random numbers, however, are difficult to
characterize mathematically, and their generation must rely on an unpredictable
physical process. Inaccuracies in the theoretical modelling of such processes
or failures of the devices, possibly due to adversarial attacks, limit the
reliability of random number generators in ways that are difficult to control
and detect. Here, inspired by earlier work on nonlocality based and device
independent quantum information processing, we show that the nonlocal
correlations of entangled quantum particles can be used to certify the presence
of genuine randomness. It is thereby possible to design of a new type of
cryptographically secure random number generator which does not require any
assumption on the internal working of the devices. This strong form of
randomness generation is impossible classically and possible in quantum systems
only if certified by a Bell inequality violation. We carry out a
proof-of-concept demonstration of this proposal in a system of two entangled
atoms separated by approximately 1 meter. The observed Bell inequality
violation, featuring near-perfect detection efficiency, guarantees that 42 new
random numbers are generated with 99% confidence. Our results lay the
groundwork for future device-independent quantum information experiments and
for addressing fundamental issues raised by the intrinsic randomness of quantum
theory.Comment: 10 pages, 3 figures, 16 page appendix. Version as close as possible
to the published version following the terms of the journa
Bell inequalities from no-signaling distributions
A Bell inequality is a constraint on a set of correlations whose violation
can be used to certify non-locality. They are instrumental for
device-independent tasks such as key distribution or randomness expansion. In
this work we consider bipartite Bell inequalities where two parties have
and possible inputs and give and possible outputs, referring
to this as the scenario. By exploiting knowledge of the
set of extremal no-signalling distributions, we find all 175 Bell inequality
classes in the (4, 4, 2, 2) scenario, as well as providing a partial list of
18277 classes in the (4, 5, 2, 2) scenario. We also use a probabilistic
algorithm to obtain 5 classes of inequality in the (2, 3, 3, 2) scenario, which
we confirmed to be complete, 25 classes in the (3, 3, 2, 3) scenario, and a
partial list of 21170 classes in the (3, 3, 3, 3) scenario. Our inequalities
are given in supplementary files. Finally, we discuss the application of these
inequalities to the detection loophole problem, and provide new lower bounds on
the detection efficiency threshold for small numbers of inputs and outputs.Comment: 15 + 7 pages. v2: more scenarios are covered and more analysis has
been done. v3: shorter title and a few additional updates, including summary
table
Therapeutic potential of TLR8 agonist GS-9688 (selgantolimod) in chronic hepatitis B: re-modelling of antiviral and regulatory mediators
Background & Aims:
GSâ9688 (selgantolimod) is a tollâlike receptor 8 (TLR8) agonist in clinical development for the treatment of chronic hepatitis B (CHB). Antiviral activity of GSâ9688 has previously been evaluated in vitro in hepatitis B virus (HBV)âinfected hepatocytes and in vivo in the woodchuck model of CHB. Here we evaluated the potential of GSâ9688 to boost responses contributing to viral control and to modulate regulatory mediators.
Approach & Results:
We characterised the effect of GSâ9688 on immune cell subsets in vitro in PBMC of healthy controls and CHB patients. GSâ9688 activated dendritic cells and mononuclear phagocytes to produce ILâ12 and other immunomodulatory mediators, inducing a comparable cytokine profile in healthy controls and CHB patients. GSâ9688 increased the frequency of activated natural killer (NK) cells, mucosalâassociated invariant Tâcells (MAITs), CD4+ follicular helper Tâcells (TFH) and, in ~50% of patients, HBVâspecific CD8+Tâcells expressing interferonâÎł (IFNÎł). Moreover, in vitro stimulation with GSâ9688 induced NK cell expression of IFNÎł and TNFα and promoted hepatocyte lysis. We also assessed whether GSâ9688 inhibited immunosuppressive cell subsets that might enhance antiviral efficacy. Stimulation with GSâ9688 reduced the frequency of CD4+ regulatory Tâcells and monocytic myeloidâderived suppressor cells (MDSC). Residual MDSC expressed higher levels of negative immune regulators, galectinâ9 and PDâL1. Conversely, GSâ9688 induced an expansion of immunoregulatory TNFârelated apoptosisâinducing ligand+ (TRAIL) regulatory NK cells and degranulation of arginaseâI+ polymorphonuclearâMDSC (PMNâMDSC).
Conclusions:
GSâ9688 induces cytokines in human PBMC that are able to activate antiviral effector function by multiple immune mediators (HBVâspecific CD8+Tâcells, TFH, NK cells and MAITs). Whilst reducing the frequency of some immunoregulatory subsets, it enhances the immunosuppressive potential of others, highlighting potential biomarkers and immunotherapeutic targets to optimise the antiviral efficacy of GSâ9688
Quantum Tasks in Minkowski Space
The fundamental properties of quantum information and its applications to
computing and cryptography have been greatly illuminated by considering
information-theoretic tasks that are provably possible or impossible within
non-relativistic quantum mechanics. I describe here a general framework for
defining tasks within (special) relativistic quantum theory and illustrate it
with examples from relativistic quantum cryptography and relativistic
distributed quantum computation. The framework gives a unified description of
all tasks previously considered and also defines a large class of new questions
about the properties of quantum information in relation to Minkowski causality.
It offers a way of exploring interesting new fundamental tasks and
applications, and also highlights the scope for a more systematic understanding
of the fundamental information-theoretic properties of relativistic quantum
theory
Simulations of quantum double models
We demonstrate how to build a simulation of two dimensional physical theories
describing topologically ordered systems whose excitations are in one to one
correspondence with irreducible representations of a Hopf algebra, D(G), the
quantum double of a finite group G. Our simulation uses a digital sequence of
operations on a spin lattice to prepare a ground "vacuum" state and to create,
braid and fuse anyonic excitations. The simulation works with or without the
presence of a background Hamiltonian though only in the latter case is the
system topologically protected. We describe a physical realization of a
simulation of the simplest non-Abelian model, D(S_3), using trapped neutral
atoms in a two dimensional optical lattice and provide a sequence of steps to
perform universal quantum computation with anyons. The use of ancillary spin
degrees of freedom figures prominently in our construction and provides a novel
technique to prepare and probe these systems.Comment: 24 pages, 2 figure
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