Sized Types for Low-Level Quantum Metaprogramming

Abstract

One of the most fundamental aspects of quantum circuit design is the concept of families of circuits parametrized by an instance size. As in classical programming, metaprogramming allows the programmer to write entire families of circuits simultaneously, an ability which is of particular importance in the context of quantum computing as algorithms frequently use arithmetic over non-standard word lengths. In this work, we introduce metaQASM, a typed extension of the openQASM language supporting the metaprogramming of circuit families. Our language and type system, built around a lightweight implementation of sized types, supports subtyping over register sizes and is moreover typesafe. In particular, we prove that our system is strongly normalizing, and as such any well-typed metaQASM program can be statically unrolled into a finite circuit.

A verified optimizer for Quantum circuits

“…We can verify compilation from high-level languages with formal semantics like Silq [Bichsel et al 2020] to sqir circuits. We can implement validated parsers [Jourdan et al 2012] for languages like OpenQASM and verify their translation to sqir (e.g., using metaQASM's semantics [Amy 2019]); this work is already in progress [Singhal et al 2020]. We can also add support for hardware-specific transformations that compile to a particular gate set.…”

OpenQASM 3: A broader and deeper quantum assembly language

“…For low-level platform-specific OpenQASM circuits, we introduce syntax for defining arbitrary bit widths of classical types. In addition to the hardware-agnostic int type Open-QASM 3 also allows programmers to specify an integer with exact precision int[n] for any positive integer n. For example, uint [8] x = 0; // some time later... bit a = x [2]; // read the 3rd least-significant bit of 'x' and assign it to 'a'…”

“…We expect similar kinds of manipulations to be common in OpenQASM 3, and so we allow for direct access to bit-level updates within classical values. In practice, we expect target platforms for OpenQASM 3 to only support particular bit widths of each classical type: e.g., some target hardware might only allow for uint [8] and uint [16], while other targets might only offer uint [20]. This is intended to allow OpenQASM 3 to describe platform-specific code which is tailored to the registers and other resources of controllers of a quantum circuit unit.…”

“…In the period since OpenQASM 2 was introduced, it has become something of a de facto standard, allowing a number of independent tools to inter-operate using OpenQASM 2 as the common interchange format. It also exists within the context of significant other activity in exploring and defining quantum assembly languages for practical use [8][9][10][11][12][13][14]. These machine-independent languages traditionally describe quantum computation in the quantum circuit model [15][16][17].…”

staq -- A full-stack quantum processing toolkit

“…These extensions are described in more detail in Section 2.2. Future planned versions will support iteration and register arguments to gates à la metaQASM [16].…”