  The impossibility of creating perfect identical copies of unknown quantum
systems is a fundamental concept in quantum theory and one of the main
non-classical properties of quantum information. This limitation imposed by
quantum mechanics, famously known as the no-cloning theorem, has played a
central role in quantum cryptography as a key component in the security of
quantum protocols. In this thesis, we look at Unclonability in a broader
context in physics and computer science and more specifically through the lens
of cryptography, learnability and hardware assumptions. We introduce new
notions of unclonability in the quantum world, namely quantum physical
unclonability, and study the relationship with cryptographic properties and
assumptions such as unforgeability, and quantum pseudorandomness. The purpose
of this study is to bring new insights into the field of quantum cryptanalysis
and into the notion of unclonability itself. We also discuss several
applications of this new type of unclonability as a cryptographic resource for
designing provably secure quantum protocols. Furthermore, we present a new
practical cryptanalysis technique concerning the problem of approximate cloning
of quantum states. We design a quantum machine learning-based cryptanalysis
algorithm to demonstrate the power of quantum learning tools as both attack
strategies and powerful tools for the practical study of quantum unclonability.
