380 research outputs found
Reachability and Termination Analysis of Concurrent Quantum Programs
We introduce a Markov chain model of concurrent quantum programs. This model
is a quantum generalization of Hart, Sharir and Pnueli's probabilistic
concurrent programs. Some characterizations of the reachable space, uniformly
repeatedly reachable space and termination of a concurrent quantum program are
derived by the analysis of their mathematical structures. Based on these
characterizations, algorithms for computing the reachable space and uniformly
repeatedly reachable space and for deciding the termination are given.Comment: Accepted by Concur'12. Comments are welcom
Model checking quantum Markov chains
Although the security of quantum cryptography is provable based on the
principles of quantum mechanics, it can be compromised by the flaws in the
design of quantum protocols and the noise in their physical implementations.
So, it is indispensable to develop techniques of verifying and debugging
quantum cryptographic systems. Model-checking has proved to be effective in the
verification of classical cryptographic protocols, but an essential difficulty
arises when it is applied to quantum systems: the state space of a quantum
system is always a continuum even when its dimension is finite. To overcome
this difficulty, we introduce a novel notion of quantum Markov chain, specially
suited to model quantum cryptographic protocols, in which quantum effects are
entirely encoded into super-operators labelling transitions, leaving the
location information (nodes) being classical. Then we define a quantum
extension of probabilistic computation tree logic (PCTL) and develop a
model-checking algorithm for quantum Markov chains.Comment: Journal versio
A Sample-Driven Solving Procedure for the Repeated Reachability of Quantum CTMCs
Reachability analysis plays a central role in system design and verification.
The reachability problem, denoted , asks whether the system
will meet the property after some time in a given time interval .
Recently, it has been considered on a novel kind of real-time systems --
quantum continuous-time Markov chains (QCTMCs), and embedded into the
model-checking algorithm. In this paper, we further study the repeated
reachability problem in QCTMCs, denoted , which
concerns whether the system starting from each \emph{absolute} time in will
meet the property after some coming \emph{relative} time in . First
of all, we reduce it to the real root isolation of a class of real-valued
functions (exponential polynomials), whose solvability is conditional to
Schanuel's conjecture being true. To speed up the procedure, we employ the
strategy of sampling. The original problem is shown to be equivalent to the
existence of a finite collection of satisfying samples. We then present a
sample-driven procedure, which can effectively refine the sample space after
each time of sampling, no matter whether the sample itself is successful or
conflicting. The improvement on efficiency is validated by randomly generated
instances. Hence the proposed method would be promising to attack the repeated
reachability problems together with checking other -regular properties
in a wide scope of real-time systems
Bounded Model Checking for Probabilistic Programs
In this paper we investigate the applicability of standard model checking
approaches to verifying properties in probabilistic programming. As the
operational model for a standard probabilistic program is a potentially
infinite parametric Markov decision process, no direct adaption of existing
techniques is possible. Therefore, we propose an on-the-fly approach where the
operational model is successively created and verified via a step-wise
execution of the program. This approach enables to take key features of many
probabilistic programs into account: nondeterminism and conditioning. We
discuss the restrictions and demonstrate the scalability on several benchmarks
(Un)decidable Problems about Reachability of Quantum Systems
We study the reachability problem of a quantum system modelled by a quantum
automaton. The reachable sets are chosen to be boolean combinations of (closed)
subspaces of the state space of the quantum system. Four different reachability
properties are considered: eventually reachable, globally reachable, ultimately
forever reachable, and infinitely often reachable. The main result of this
paper is that all of the four reachability properties are undecidable in
general; however, the last three become decidable if the reachable sets are
boolean combinations without negation
Model checking ω-regular properties for quantum Markov chains
© Yuan Feng, Ernst Moritz Hahn, Andrea Turrini, and Shenggang Ying. Quantum Markov chains are an extension of classical Markov chains which are labelled with super-operators rather than probabilities. They allow to faithfully represent quantum programs and quantum protocols. In this paper, we investigate model checking !-regular properties, a very general class of properties (including, e.g., LTL properties) of interest, against this model. For classical Markov chains, such properties are usually checked by building the product of the model with a language automaton. Subsequent analysis is then performed on this product. When doing so, one takes into account its graph structure, and for instance performs different analyses per bottom strongly connected component (BSCC). Unfortunately, for quantum Markov chains such an approach does not work directly, because super-operators behave differently from probabilities. To overcome this problem, we transform the product quantum Markov chain into a single super-operator, which induces a decomposition of the state space (the tensor product of classical state space and the quantum one) into a family of BSCC subspaces. Interestingly, we show that this BSCC decomposition provides a solution to the issue of model checking ω-regular properties for quantum Markov chains
Decomposition of quantum Markov chains and its applications
© 2018 Elsevier Inc. Markov chains have been widely employed as a fundamental model in the studies of probabilistic and stochastic communicating and concurrent systems. It is well-understood that decomposition techniques play a key role in reachability analysis and model-checking of Markov chains. (Discrete-time) quantum Markov chains have been introduced as a model of quantum communicating systems [1] and also a semantic model of quantum programs [2]. The BSCC (Bottom Strongly Connected Component) and stationary coherence decompositions of quantum Markov chains were introduced in [3–5]. This paper presents a new decomposition technique, namely periodic decomposition, for quantum Markov chains. We further establish a limit theorem for them. As an application, an algorithm to find a maximum dimensional noiseless subsystem of a quantum communicating system is given using decomposition techniques of quantum Markov chains
Counterexample Generation in Probabilistic Model Checking
Providing evidence for the refutation of a property is an essential, if not the most important, feature of model checking. This paper considers algorithms for counterexample generation for probabilistic CTL formulae in discrete-time Markov chains. Finding the strongest evidence (i.e., the most probable path) violating a (bounded) until-formula is shown to be reducible to a single-source (hop-constrained) shortest path problem. Counterexamples of smallest size that deviate most from the required probability bound can be obtained by applying (small amendments to) k-shortest (hop-constrained) paths algorithms. These results can be extended to Markov chains with rewards, to LTL model checking, and are useful for Markov decision processes. Experimental results show that typically the size of a counterexample is excessive. To obtain much more compact representations, we present a simple algorithm to generate (minimal) regular expressions that can act as counterexamples. The feasibility of our approach is illustrated by means of two communication protocols: leader election in an anonymous ring network and the Crowds protocol
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