We develop a linear logical framework within the Hybrid system and use it to reason about the type system of a quantum lambda calculus. In particular, we consider a practical version of the calculus called Proto-Quipper, which contains the core of Quipper. Quipper is a new quantum programming language under active development and recently has gained much popularity among the quantum computing communities. Hybrid is a system that is designed to support the use of higher-order abstract syntax (HOAS) for representing and reasoning about formal systems implemented in the Coq Proof Assistant. In this work, we extend the system with a linear specification logic (SL) in order to reason about the linear type system of Quipper. To this end, we formalize the semantics of Proto-Quipper by encoding the typing and evaluation rules in the SL, and prove type soundness.
The Proto-Quipper family of programming languages aims to provide a formal foundation for the Quipper quantum programming language. Unfortunately, Proto-Quipper languages have complex operational semantics: they are inherently effectful, and they rely on set-theoretic operations and fresh name generation to manipulate quantum circuits. This makes them difficult to reason about using standard programming language techniques and, ultimately, to mechanize. We introduce Proto-Quipper-A, a rational reconstruction of Proto-Quipper languages for static circuit generation. It uses a linear
λ-calculus to describe quantum circuits with normal forms that closely correspond to box-and-wire circuit diagrams. Adjoint-logical foundations integrate this circuit language with a linear/non-linear functional language and let us reconstruct Proto-Quipper's circuit programming abstractions using more primitive adjoint-logical operations. Proto-Quipper-A enjoys a simple call-by-value reduction semantics, and to illustrate its tractability as a foundation for Proto-Quipper languages, we show that it is normalizing. We show how to use standard logical relations to prove normalization of linear and substructural systems, thereby avoiding the inherent complexity of existing linear logical relations.
This thesis contains contributions to the mathematical foundations of quantum programming languages. The likely arrival of scalable quantum computers in the not-so-distant future has resulted in a flurry of activity in the development of quantum programming languages. As in classical computing, the transition from a description of a quantum algorithm found in the literature to a hardware-specific set of instructions run on a quantum device is a complex process, prone to errors. This issue is exacerbated in the quantum setting not only by the complexity of quantum algorithms but also by the fragility of quantum information, which renders ineffective some of the classical techniques used to debug programs. In this thesis, we contribute to the solution of some of these issues. We introduce Proto-Quipper-M, a new quantum programming language designed to serve as a testbed for the research and development of sound mathematical semantics and reasoning techniques for quantum programs. We first present Proto-Quipper-M as a formalization of a fragment of Quipper, a high-level functional programming language for describing families of quantum circuits. In particular, we define Proto-Quipper-M as a simply-typed lambda calculus with a special type for quantum circuits and a strong type system designed to enforce linearity on quantum data, and thus prevent violations of the no-cloning property of quantum information. We endow Proto-Quipper-M with computational meaning via a big-step operational semantics and prove that the language is type-safe by showing that it enjoys the type-preservation and error-freeness properties. We also give Proto-Quipper-M a denotational semantics in a suitable class of monoidal categories and show that these categories give rise to linear-non-linear models in the sense of Benton, and thus models of intuitionistic linear logic. Finally, we crystallize the connection between the syntax and the semantics of the language by proving the soundness theorem for Proto-Quipper-M.