The Quantum Intermediate Representation (QIR) Alliance is a Linux Foundation standards effort announced in 2021 to develop a shared compiler interface for quantum programs. QIR is based on LLVM IR, placing it between quantum programming languages and platform-specific compilers. It is designed to help tools and platforms work together—not to make every program run on every quantum computer automatically.
What is the QIR Alliance?
The Linux Foundation announced the QIR Alliance on November 30, 2021, as a joint effort to establish an intermediate representation for quantum programs. Its stated goal is to support interoperability across the quantum-computing ecosystem and provide a representation suited to different kinds of quantum processors. The announcement named Honeywell, Microsoft, Oak Ridge National Laboratory, Quantum Circuits Inc., and Rigetti Computing as founding members. The Linux Foundation announcement is the source for that dated founding list.
A Microsoft technical overview updated February 14, 2025, describes the founding members differently, listing Microsoft, Quantinuum, Oak Ridge National Laboratory, Quantum Circuits Inc., and Rigetti Computing. These two sources do not establish the Alliance’s current membership roster, so neither list should be treated as a definitive current membership statement. Microsoft’s QIR overview explains the technical design.
What does QIR stand for, and where does it fit?
QIR stands for Quantum Intermediate Representation. An intermediate representation, or IR, is a compiler’s middle layer: a front end translates a source language into the IR, and a back end translates that representation into code for a particular target. In principle, multiple language front ends and target back ends can share this layer and some compiler tools, provided their implementations support the relevant features.
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QIR uses LLVM’s intermediate representation to express quantum-program constructs under LLVM’s rules. Microsoft says QIR does not require extensions or modifications to LLVM. In the intended compiler flow, a programming framework produces QIR, then a target-specific back end prepares it for a quantum platform or simulator.
How does QIR connect languages to quantum computers?
- Translate the program: A language or framework’s front end converts the program into QIR.
- Process the representation: LLVM-based compiler infrastructure can be used for tasks such as optimization. The Alliance announcement and Microsoft overview describe shared optimizer and tool-reuse scenarios as intended uses.
- Compile for a target: A compatible, platform-specific back end translates the supported QIR constructs into instructions and execution requirements for a particular environment.
- Run or simulate: The target environment executes the compiled program, or a compatible simulator runs it. The representation alone does not provide a device, runtime, or execution service.
QIR is hardware-agnostic in the specific sense that it does not prescribe a quantum gate set or instruction set. The target environment supplies those hardware-specific details. That separation can make compiler components reusable, but a target still needs a back end and support for the QIR features used by a program.
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Is QIR specific to Q#?
No. QIR is intended as a common representation for quantum programming frameworks, rather than a format exclusive to Microsoft’s Q# language. Microsoft’s overview illustrates Q# operations represented as LLVM functions, but that example demonstrates the representation’s use; it does not establish universal compatibility with other languages or devices.
Whether another framework or platform can use QIR depends on its front end, back end, and the features each implementation supports. The official overviews do not provide an exhaustive SDK or hardware compatibility matrix, so QIR should not be read as a guarantee that any QIR program can move unchanged between providers.
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What can developers use QIR for?
The Alliance announcement and Microsoft’s overview describe several possible applications of a shared representation:
- Building optimizer passes that operate on QIR and can be paired with hardware-specific back ends.
- Reusing compiler infrastructure across compatible quantum languages and target platforms.
- Representing hybrid programs that combine classical control flow and quantum operations.
- Connecting quantum programs with classical high-performance libraries for simulation.
These are described capabilities and use cases, not reported performance results or proof of broad adoption. The sources provide no quantified speedup, cost saving, or compatibility rate.
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What is established—and what remains unclear?
- Established: QIR is an LLVM-based intermediate representation intended to provide a common compiler layer for quantum programs, and the Alliance was announced by the Linux Foundation in 2021.
- Not established by the cited official overviews: a current QIR specification version, a complete feature or profile status, an exhaustive list of supported SDKs and hardware back ends, or the Alliance’s current membership and governance roster.
For a practical compatibility decision, check whether the specific framework can emit the QIR features your program needs and whether the intended platform’s back end and runtime support them. “Common interface” describes the design aim; it does not remove target-specific compilation or execution requirements.
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