4,046 research outputs found
How to Incentivize Data-Driven Collaboration Among Competing Parties
The availability of vast amounts of data is changing how we can make medical
discoveries, predict global market trends, save energy, and develop educational
strategies. In some settings such as Genome Wide Association Studies or deep
learning, sheer size of data seems critical. When data is held distributedly by
many parties, they must share it to reap its full benefits.
One obstacle to this revolution is the lack of willingness of different
parties to share data, due to reasons such as loss of privacy or competitive
edge. Cryptographic works address privacy aspects, but shed no light on
individual parties' losses/gains when access to data carries tangible rewards.
Even if it is clear that better overall conclusions can be drawn from
collaboration, are individual collaborators better off by collaborating?
Addressing this question is the topic of this paper.
* We formalize a model of n-party collaboration for computing functions over
private inputs in which participants receive their outputs in sequence, and the
order depends on their private inputs. Each output "improves" on preceding
outputs according to a score function.
* We say a mechanism for collaboration achieves collaborative equilibrium if
it ensures higher reward for all participants when collaborating (rather than
working alone). We show that in general, computing a collaborative equilibrium
is NP-complete, yet we design efficient algorithms to compute it in a range of
natural model settings.
Our collaboration mechanisms are in the standard model, and thus require a
central trusted party; however, we show this assumption is unnecessary under
standard cryptographic assumptions. We show how to implement the mechanisms in
a decentralized way with new extensions of secure multiparty computation that
impose order/timing constraints on output delivery to different players, as
well as privacy and correctness
Rational Multiparty Computation
The field of rational cryptography considers the design of cryptographic protocols in the presence of rational agents seeking to maximize local utility functions. This departs from the standard secure multiparty computation setting, where players are assumed to be either honest or malicious. ^ We detail the construction of both a two-party and a multiparty game theoretic framework for constructing rational cryptographic protocols. Our framework specifies the utility function assumptions necessary to realize the privacy, correctness, and fairness guarantees for protocols. We demonstrate that our framework correctly models cryptographic protocols, such as rational secret sharing, where existing work considers equilibrium concepts that yield unreasonable equilibria. Similarly, we demonstrate that cryptography may be applied to the game theoretic domain, constructing an auction market not realizable in the original formulation. Additionally, we demonstrate that modeling players as rational agents allows us to design a protocol that destabilizes coalitions. Thus, we establish a mutual benefit from combining the two fields, while demonstrating the applicability of our framework to real-world market environments.^ We also give an application of game theory to adversarial interactions where cryptography is not necessary. Specifically, we consider adversarial machine learning, where the adversary is rational and reacts to the presence of a data miner. We give a general extension to classification algorithms that returns greater expected utility for the data miner than existing classification methods
Quantum simulation of zero temperature quantum phases and incompressible states of light via non-Markovian reservoir engineering techniques
We review recent theoretical developments on the stabilization of strongly
correlated quantum fluids of light in driven-dissipative photonic devices
through novel non-Markovian reservoir engineering techniques. This approach
allows to compensate losses and refill selectively the photonic population so
to sustain a desired steady-state. It relies in particular on the use of a
frequency-dependent incoherent pump which can be implemented, e.g., via
embedded two-level systems maintained at a strong inversion of population. As
specific applications of these methods, we discuss the generation of Mott
Insulator (MI) and Fractional Quantum Hall (FQH) states of light. As a first
step, we present the case of a narrowband emission spectrum and show how this
allows for the stabilization of MI and FQH states under the condition that the
photonic states are relatively flat in energy. As soon as the photonic
bandbwidth becomes comparable to the emission linewidth, important
non-equilibrium signatures and entropy generation appear. As a second step, we
review a more advanced configuration based on reservoirs with a broadband
frequency distribution, and we highlight the potential of this configuration
for the quantum simulation of equilibrium quantum phases at zero temperature
with tunable chemical potential. As a proof of principle we establish the
applicability of our scheme to the Bose-Hubbard model by confirming the
presence of a perfect agreement with the ground-state predictions both in the
Mott Insulating and superfluid regions, and more generally in all parts of the
parameter space. Future prospects towards the quantum simulation of more
complex configurations are finally outlined, along with a discussion of our
scheme as a concrete realization of quantum annealing
Perfect Implementation of Normal-Form Mechanisms
Privacy and trust affect our strategic thinking, yet they have not been precisely modeled in mechanism design. In settings of incomplete information, traditional implementations of a normal-form mechanism ---by disregarding the players' privacy, or assuming trust in a mediator--- may not be realistic and fail to reach the mechanism's objectives. We thus investigate implementations of a new type.We put forward the notion of a perfect implementation of a normal-form mechanism M: in essence, an extensive-form mechanism exactly preserving all strategic properties of M, WITHOUT relying on a trusted mediator or violating the privacy of the players. We prove that ANY normal-form mechanism can be perfectly implemented by a PUBLIC mediator using envelopes and an envelope-randomizing device (i.e., the same tools used for running fair lotteries or tallying secret votes). Differently from a trusted mediator, a public one only performs prescribed public actions, so that everyone can verify that he is acting properly, and never learns any information that should remain private
Quasiclassical Coarse Graining and Thermodynamic Entropy
Our everyday descriptions of the universe are highly coarse-grained,
following only a tiny fraction of the variables necessary for a perfectly
fine-grained description. Coarse graining in classical physics is made natural
by our limited powers of observation and computation. But in the modern quantum
mechanics of closed systems, some measure of coarse graining is inescapable
because there are no non-trivial, probabilistic, fine-grained descriptions.
This essay explores the consequences of that fact. Quantum theory allows for
various coarse-grained descriptions some of which are mutually incompatible.
For most purposes, however, we are interested in the small subset of
``quasiclassical descriptions'' defined by ranges of values of averages over
small volumes of densities of conserved quantities such as energy and momentum
and approximately conserved quantities such as baryon number. The
near-conservation of these quasiclassical quantities results in approximate
decoherence, predictability, and local equilibrium, leading to closed sets of
equations of motion. In any description, information is sacrificed through the
coarse graining that yields decoherence and gives rise to probabilities for
histories. In quasiclassical descriptions, further information is sacrificed in
exhibiting the emergent regularities summarized by classical equations of
motion. An appropriate entropy measures the loss of information. For a
``quasiclassical realm'' this is connected with the usual thermodynamic entropy
as obtained from statistical mechanics. It was low for the initial state of our
universe and has been increasing since.Comment: 17 pages, 0 figures, revtex4, Dedicated to Rafael Sorkin on his 60th
birthday, minor correction
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