Catalyst Runtime

The Catalyst Runtime is a C++ QIR runtime that enables the execution of Catalyst-compiled quantum programs, and is currently backed by state-vector simulators PennyLane-Lightning and Pennylane-Lightning-Kokkos.

The runtime employs the QuantumDevice public interface to support an extensible list of backend devices. This interface comprises two collections of abstract methods:

• The Qubit management, device shot noise, and quantum tape recording methods are utilized for the implementation of Quantum Runtime (QR) instructions.

• The quantum operations, observables, measurements, and gradient methods are used to implement Quantum Instruction Set (QIS) instructions.

A complete list of instructions supported by the runtime can be found in RuntimeCAPI.h.

Contents

The directory is structured as follows:

• include:

  This contains the public header files of the runtime including the QuantumDevice API for backend quantum devices and the runtime CAPI.

• extensions:

  A collection of extensions for backend simulators to fit into the QIR programming model. The StateVectorDynamicCPU class extends the state-vector class of Pennylane-Lightning providing dynamic allocation and deallocation of qubits.

• lib:

  The core modules of the runtime are structured into lib/capi and lib/backend. lib/capi implements the bridge between QIR instructions in LLVM-IR and C++ device backends. lib/backend contains implementations of the QuantumDevice API for backend simulators.

• tests:

  A collection of C++ tests for modules and methods in the runtime.

Backend Devices

New device backends for the runtime can be realized by implementing the quantum device interface. The following table shows the available devices along with supported features:

Features	PennyLane-Lightning	PennyLane-Lightning-Kokkos
Qubit Management	Dynamic allocation/deallocation	Static allocation/deallocation
Gate Operations	Lightning operations	Lightning operations
Quantum Observables	Identity, PauliX, PauliY, PauliZ, Hadamard, Hermitian, Hamiltonian, and Tensor Product of Observables	Identity, PauliX, PauliY, PauliZ, Hadamard, Hermitian, Hamiltonian, and Tensor Product of Observables
Expectation Value	All observables; Finite-shots not supported	All observables; Finite-shots not supported
Variance	Only for Identity, PauliX, PauliY, PauliZ, and Hadamard; Finite-shots not supported	All observables; Finite-shots not supported
Probability	Only for the computational basis on the supplied qubits; Finite-shots not supported	Only for the computational basis on the supplied qubits; Finite-shots not supported
Sampling	Only for the computational basis on the supplied qubits	Only for the computational basis on the supplied qubits
Mid-Circuit Measurement	Only for the computational basis on the supplied qubit	Only for the computational basis on the supplied qubit
Gradient	The Adjoint-Jacobian method for expectation values on all observables	The Adjoint-Jacobian method for expectation values on all observables

Requirements

To build the runtime from source, it is required to have an up to date version of a C/C++ compiler such as gcc or clang with support for the C++20 standard library and the static library of stdlib from qir-runner.

The runtime leverages the stdlib Rust package for the QIR standard runtime instructions. To build this package from source, the Rust toolchain installed via rustup is also required.

Installation

By default, the runtime leverages Pennylane-Lightning as the backend simulator. You can use the CMake flag -DENABLE_LIGHTNING_KOKKOS to build the runtime with Pennylane-Lightning-Kokkos in the serial mode or run:

ENABLE_KOKKOS=ON make runtime

Lightning-Kokkos provides support for other Kokkos backends including OpenMP, HIP and CUDA. Please refer to the installation guideline for the requirements.

The runtime uses the QIR standard library for basic QIR instructions. Before building stdlib, the llvm-tools-preview Rustup component needs to be installed:

rustup component add llvm-tools-preview

To build the static library of stdlib:

make qir

And use CMake flags -DQIR_STDLIB_LIB and -DQIR_STDLIB_INCLUDES to respectively locate libqir_stdlib.a and qir_stdlib.h, or run:

QIR_STDLIB_DIR=$(pwd)/qir-stdlib/target/release QIR_STDLIB_INCLUDES_DIR=$(pwd)/qir-stdlib/target/release/build/include make runtime

To check the runtime test suite:

make test

You can also build and test the runtime (and qir-stdlib) from the top level directory via make runtime and make test-runtime.

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