4,197 research outputs found
Stabilizer States as a Basis for Density Matrices
We show that the space of density matrices for n-qubit states, considered as
a (2^n)^2 dimensional real vector space, has a basis consisting of density
matrices of stabilizer states. We describe an application of this result to
automated verification of quantum protocols
Benefits of Session Types for software Development
Session types are a formalism used to specify and check the correctness of communication based systems. Within their scope, they can guarantee the absence of communication errors such as deadlock, sending an unexpected message or failing to handle an incoming message. Introduced over two decades ago, they have developed into a significant theme in programming languages. In this paper we examine the beliefs that drive research into this area and make it popular. We look at the claims and motivation behind session types throughout the literature. We identify the hypotheses upon which session types have been designed and implemented, and attempt to clarify and formulate them in a more suitable manner for testing
Session Types as Generic Process Types
Behavioural type systems ensure more than the usual safety guarantees of
static analysis. They are based on the idea of "types-as-processes", providing
dedicated type algebras for particular properties, ranging from protocol
compatibility to race-freedom, lock-freedom, or even responsiveness. Two
successful, although rather different, approaches, are session types and
process types. The former allows to specify and verify (distributed)
communication protocols using specific type (proof) systems; the latter allows
to infer from a system specification a process abstraction on which it is
simpler to verify properties, using a generic type (proof) system. What is the
relationship between these approaches? Can the generic one subsume the specific
one? At what price? And can the former be used as a compiler for the latter?
The work presented herein is a step towards answers to such questions.
Concretely, we define a stepwise encoding of a pi-calculus with sessions and
session types (the system of Gay and Hole) into a pi-calculus with process
types (the Generic Type System of Igarashi and Kobayashi). We encode session
type environments, polarities (which distinguish session channels end-points),
and labelled sums. We show forward and reverse operational correspondences for
the encodings, as well as typing correspondences. To faithfully encode session
subtyping in process types subtyping, one needs to add to the target language
record constructors and new subtyping rules. In conclusion, the programming
convenience of session types as protocol abstractions can be combined with the
simplicity and power of the pi-calculus, taking advantage in particular of the
framework provided by the Generic Type System.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
Session Types for Broadcasting
Up to now session types have been used under the assumptions of point to
point communication, to ensure the linearity of session endpoints, and reliable
communication, to ensure send/receive duality. In this paper we define a
session type theory for broadcast communication semantics that by definition do
not assume point to point and reliable communication. Our session framework
lies on top of the parametric framework of broadcasting psi-calculi, giving
insights on developing session types within a parametric framework. Our session
type theory enjoys the properties of soundness and safety. We further believe
that the solutions proposed will eventually provide a deeper understanding of
how session types principles should be applied in the general case of
communication semantics.Comment: In Proceedings PLACES 2014, arXiv:1406.331
Execution Models for Choreographies and Cryptoprotocols
A choreography describes a transaction in which several principals interact.
Since choreographies frequently describe business processes affecting
substantial assets, we need a security infrastructure in order to implement
them safely. As part of a line of work devoted to generating cryptoprotocols
from choreographies, we focus here on the execution models suited to the two
levels.
We give a strand-style semantics for choreographies, and propose a special
execution model in which choreography-level messages are faithfully delivered
exactly once. We adapt this model to handle multiparty protocols in which some
participants may be compromised.
At level of cryptoprotocols, we use the standard Dolev-Yao execution model,
with one alteration. Since many implementations use a "nonce cache" to discard
multiply delivered messages, we provide a semantics for at-most-once delivery
Verification of Linear Optical Quantum Computing using Quantum Process Calculus
We explain the use of quantum process calculus to describe and analyse linear
optical quantum computing (LOQC). The main idea is to define two processes, one
modelling a linear optical system and the other expressing a specification, and
prove that they are behaviourally equivalent. We extend the theory of
behavioural equivalence in the process calculus Communicating Quantum Processes
(CQP) to include multiple particles (namely photons) as information carriers,
described by Fock states or number states. We summarise the theory in this
paper, including the crucial result that equivalence is a congruence, meaning
that it is preserved by embedding in any context. In previous work, we have
used quantum process calculus to model LOQC but without verifying models
against specifications. In this paper, for the first time, we are able to carry
out verification. We illustrate this approach by describing and verifying two
models of an LOQC CNOT gate.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
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