
gates to represent the conditional probability tables
associated with the Survival node (see Fig. 2).
2.3 Fuzzy Models
Fuzzy logic is a form of many-valued logic in which
the truth value of the variables can be any real number
between 0 and 1. The term was introduced with the
1965 proposal of fuzzy set theory by scientist Lotfi
A. Zadeh (Zadeh, 1965). In these models, impreci-
sion is represented by a fuzzification process in which
a numeric input is assigned to a given fuzzy set with
some degree of membership. Uncertainty is propa-
gated through the system using a fuzzy implication
function that triggers partially, and in parallel, several
rules that include those fuzzy sets with some degree
of membership different from zero. The final step is
the defuzzification process, in which the fuzzy results
are converted back into crisp results.
It is easy to see the parallelism between fuzzy
models and quantum computing. The fuzzification
process puts a given crisp value in a sort of “super-
position” of several fuzzy variables (a person can be
considered tall and short at the same time with dif-
ferent degrees of membership). The defuzzification
process is the counterpart to the measure in quantum
computers, the superposition disappears but affects
how a new crisp value is obtained.
But the similarities end there, quantum mechan-
ics is based on the Hilbert space formalism and has a
probabilistic nature. On the other hand, fuzzy logic
takes the concept of intersection, union, and implica-
tion of classic logic and converts them to t-norms, t-
conorms, and fuzzy implications that can have several
different implementations.
There are several attempts to implement fuzzy
logic in a quantum computer, among the early works
we can highlight (Mannucci, 2006) and (Schmitt
et al., 2009), and among the more recent ones
(Pykacz, 2015), (Nadaban, 2021) and (Gentili, 2021).
The differences rely on how to implement the dif-
ferent fuzzy connectives as a composition of quan-
tum operations (using unitary and controlled quantum
gates) applied to quantum registers.
3 A UNIFIED VIEW OF
QUANTUM INACCURATE
KNOWLEDGE
We can see that the classical models of inaccurate
reasoning present similarities: Heckerman proposed
a probabilistic interpretation for Certainty Factors
(Heckerman, 1986) and Gentili stated that “the terms
of Bayes’ formula are describable as degrees of mem-
bership to fuzzy sets, and the Bayesian inference is
conceivable as a fuzzy inference” (Gentili, 2021).
This allows us to suggest the possibility of estab-
lishing a unified framework of these models to imple-
ment them in QC. In Table 1 we summarize the sim-
ilarities of the models when dealing with inaccuracy
and implementing them in a quantum computer.
The idea is to define of a knowledge graph and
then facilitate different of this graph as different inac-
curacy models on a quantum computer. Our first step
was the development of software (Magaz-Romero
et al., 2023) for implementing quantum rule-based
systems (QRBS) defining a classical RBS.
3.1 QRBS Software
We present a software library for the implementation
of QRBSs whose source code is available at (Consor-
tium, 2024) under an open-source license.
This software library is structured in two pack-
ages, one for encoding knowledge and one for man-
aging the quantum tasks (Moret-Bonillo et al., 2024).
The first package contains all the required ele-
ments for modeling RBSs, as illustrated in Fig. 3.
In this package we can find the following classes:
• Fact: the building block of RBSs, as it is used to
encode the declarative knowledge of the system.
• {Not,And,Or}Operator: these classes allow for
the composition of the system’s facts, each estab-
lishing a different relationship among them.
• Rule: encodes the procedural knowledge of the
system, as it relates a composition of facts (the
precedent) with a single fact (the consequent).
• KnowledgeIsland: this class aggregates different
sets of rules. The rules of a knowledge island are
those that aim at the same consequent.
The second package contains all the elements to
define a QRBS, as well as the tools to evaluate and
execute it. These components (Fig. 4) are:
• WorkingMemory, InferenceEngine: store the
declarative and procedural knowledge.
• QRBS: used to initialize the system and populate
it with the corresponding knowledge elements.
• QPU: interface defining how the QRBSs are op-
erated, with regards to evaluation and execution.
The library provides the following functionalities:
• RBS modeling: users can model a rule-based
system by encoding declarative and procedural
knowledge into a system, establishing different
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