Add Clifford-only simulator (Stim)

.gitmodules

@@ -45,3 +45,6 @@
 	path = tpls/Crow
 	url = https://github.com/CrowCpp/Crow.git
 	ignore = dirty
+[submodule "tpls/Stim"]
+	path = tpls/Stim
+	url = https://github.com/quantumlib/Stim

NOTICE

@@ -172,3 +172,11 @@ Tweedledum - MIT License
 License at <https://github.com/boschmitt/tweedledum/blob/master/LICENSE>
 
 ----------------------------------------------------------------
+
+Stim - Apache License 2.0
+<https://github.com/quantumlib/Stim>
+
+The incorporated source code and its license can be found as a submodule on the CUDA-Q repository.
+License at <https://github.com/quantumlib/Stim/blob/main/LICENSE>
+
+----------------------------------------------------------------

docs/sphinx/using/backends/backends.rst

@@ -26,6 +26,7 @@ CUDA-Q Backends
 * :ref:`qpp-cpu <qpp-cpu-backend>`
 * :ref:`quantinuum <quantinuum-backend>`
 * :ref:`remote-mqpu <mqpu-platform>`
+* :ref:`stim <stim-backend>`
 * :ref:`tensornet <tensor-backends>`
 * :ref:`tensornet-mps <tensor-backends>`
 

docs/sphinx/using/backends/simulators.rst

@@ -300,6 +300,40 @@ use the following commands:
         ./program.x
 
 
+Clifford-Only Simulation (CPU)
+++++++++++++++++++++++++++++++++++
+
+.. _stim-backend:
+
+This target provides a fast simulator for circuits containing *only* Clifford
+gates. Any non-Clifford gates (such as T gates and Toffoli gates) are not
+supported. This simulator is based on the `Stim <https://github.com/quantumlib/Stim>`_
+library.
+
+To execute a program on the :code:`stim` target, use the following commands:
+
+.. tab:: Python
+
+    .. code:: bash 
+
+        python3 program.py [...] --target stim
+
+    The target can also be defined in the application code by calling
+
+    .. code:: python 
+
+        cudaq.set_target('stim')
+
+    If a target is set in the application code, this target will override the :code:`--target` command line flag given during program invocation.
+
+.. tab:: C++
+
+    .. code:: bash 
+
+        nvq++ --target stim program.cpp [...] -o program.x
+        ./program.x
+
+
 Tensor Network Simulators
 ==================================
 

python/tests/backends/test_stim.py

@@ -0,0 +1,91 @@
+# ============================================================================ #
+# Copyright (c) 2022 - 2024 NVIDIA Corporation & Affiliates.                   #
+# All rights reserved.                                                         #
+#                                                                              #
+# This source code and the accompanying materials are made available under     #
+# the terms of the Apache License 2.0 which accompanies this distribution.     #
+# ============================================================================ #
+
+import os
+from typing import List
+import pytest
+
+import cudaq
+import numpy as np
+
+
+@pytest.fixture(scope="session", autouse=True)
+def setTarget():
+    old_target = cudaq.get_target()
+    cudaq.set_target('stim')
+    yield
+    cudaq.set_target(old_target)
+
+
+def test_stim_non_clifford():
+
+    @cudaq.kernel
+    def kernel():
+        qubits = cudaq.qvector(10)
+        rx(0.1, qubits[0])
+
+    with pytest.raises(RuntimeError) as e:
+        # Cannot perform non-Clifford gates in Stim simulator
+        cudaq.sample(kernel)
+
+
+def test_stim_toffoli_gates():
+
+    @cudaq.kernel
+    def kernel():
+        qubits = cudaq.qvector(10)
+        cx(qubits[0:9], qubits[9])
+
+    with pytest.raises(RuntimeError) as e:
+        # Cannot perform Toffoli gates in Stim simulator
+        cudaq.sample(kernel)
+
+
+def test_stim_sample():
+    # Create the kernel we'd like to execute on Stim
+    @cudaq.kernel
+    def kernel():
+        qubits = cudaq.qvector(250)
+        h(qubits[0])
+        # Stim is a Clifford-only simulator, so it can do many qubits.
+        for i in range(1, 250):
+            cx(qubits[i - 1], qubits[i])
+        mz(qubits)
+
+    counts = cudaq.sample(kernel)
+    assert (len(counts) == 2)
+    assert ('0' * 250 in counts)
+    assert ('1' * 250 in counts)
+
+
+def test_stim_state_preparation():
+
+    @cudaq.kernel
+    def kernel(vec: List[complex]):
+        qubits = cudaq.qvector(vec)
+
+    with pytest.raises(RuntimeError) as e:
+        # Cannot initialize qubits from state data in this simulator
+        state = [1. / np.sqrt(2.), 1. / np.sqrt(2.), 0., 0.]
+        cudaq.sample(kernel, state)
+
+
+def test_stim_state_preparation_builder():
+    kernel, state = cudaq.make_kernel(List[complex])
+    qubits = kernel.qalloc(state)
+
+    with pytest.raises(RuntimeError) as e:
+        # Cannot initialize qubits from state data in this simulator
+        state = [1. / np.sqrt(2.), 1. / np.sqrt(2.), 0., 0.]
+        cudaq.sample(kernel, state)
+
+
+# leave for gdb debugging
+if __name__ == "__main__":
+    loc = os.path.abspath(__file__)
+    pytest.main([loc, "-s"])

runtime/nvqir/CMakeLists.txt

@@ -38,6 +38,7 @@ install(TARGETS ${LIBRARY_NAME}
         INCLUDES DESTINATION include/nvqir)
 
 add_subdirectory(qpp)
+add_subdirectory(stim)
 
 if (CUSTATEVEC_ROOT AND CUDA_FOUND) 
   add_subdirectory(custatevec)

runtime/nvqir/CircuitSimulator.h

@@ -750,7 +750,17 @@ class CircuitSimulatorBase : public CircuitSimulator {
         summaryData.svGateUpdate(
             next.controls.size(), next.targets.size(), stateDimension,
             stateDimension * sizeof(std::complex<ScalarType>));
-      applyGate(next);
+      try {
+        applyGate(next);
+      } catch (std::exception &e) {
+        while (!gateQueue.empty())
+          gateQueue.pop();
+        throw e;
+      } catch (...) {
+        while (!gateQueue.empty())
+          gateQueue.pop();
+        throw std::runtime_error("Unknown exception in applyGate");
+      }
       if (executionContext && executionContext->noiseModel) {
         std::vector<std::size_t> noiseQubits{next.controls.begin(),
                                              next.controls.end()};

runtime/nvqir/stim/CMakeLists.txt

@@ -0,0 +1,42 @@
+# ============================================================================ #
+# Copyright (c) 2022 - 2024 NVIDIA Corporation & Affiliates.                   #
+# All rights reserved.                                                         #
+#                                                                              #
+# This source code and the accompanying materials are made available under     #
+# the terms of the Apache License 2.0 which accompanies this distribution.     #
+# ============================================================================ #
+
+set(LIBRARY_NAME nvqir-stim)
+set(INTERFACE_POSITION_INDEPENDENT_CODE ON)
+
+set(STIM_SOURCE_DIR ${CMAKE_SOURCE_DIR}/tpls/Stim)
+set(STIM_BINARY_DIR ${CMAKE_BINARY_DIR}/tpls/Stim)
+
+# The EXCLUDE_FROM_ALL makes it so that only libstim is built. If other targets
+# are desired (like the command-line tool), remove EXCLUDE_FROM_ALL below.
+add_subdirectory(${STIM_SOURCE_DIR} ${STIM_BINARY_DIR} EXCLUDE_FROM_ALL)
+
+add_library(${LIBRARY_NAME} SHARED StimCircuitSimulator.cpp)
+set_property(GLOBAL APPEND PROPERTY CUDAQ_RUNTIME_LIBS ${LIBRARY_NAME})
+
+set (STIM_DEPENDENCIES libstim fmt::fmt-header-only cudaq-common)
+
+# If -Wall is enabled (as is done in parent directories), Stim will not compile.
+# So override that here.
+target_compile_options(libstim PRIVATE -Wno-all)
+
+target_include_directories(${LIBRARY_NAME}
+    PUBLIC
+      $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+      $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/runtime>
+      $<INSTALL_INTERFACE:include>)
+
+target_link_libraries(${LIBRARY_NAME}
+  PRIVATE ${STIM_DEPENDENCIES})
+
+set_target_properties(${LIBRARY_NAME}
+    PROPERTIES INSTALL_RPATH "${CMAKE_INSTALL_RPATH}:${LLVM_BINARY_DIR}/lib")
+
+install(TARGETS ${LIBRARY_NAME} DESTINATION lib)
+
+add_target_config(stim)