In-memory quantum simulators

Quantum simulators are software programs that run on classical computers and act as the target machine for a quantum program, making it possible to run and test quantum programs in an environment that predicts how qubits will react to different operations. The Quantum Development Kit includes multiple in-memory quantum simulators that represent different ways of simulating the same quantum algorithm. In-memory simulators have the advantage of being able to run locally and thus faster, as well as running jobs as often as needed free of charge. Backend quantum simulators, however, can more accurately simulate specific hardware architecture and capabilities of each manufacturer. For more information, see Backend simulators.

The quantum simulator is responsible for providing implementations of quantum operations for an algorithm. This includes primitive operations such as H, CNOT, and Measure, as well as qubit management and tracking. Each type of quantum simulator can provide different implementations of these primitives. For example, the full state simulator runs the quantum algorithm by fully simulating the quantum state vector, whereas the quantum computer trace simulator doesn't consider the actual quantum state at all. Rather, it tracks gate, qubit, and other resource usage for the algorithm.

Quantum machine classes

In the future, the QDK will define additional quantum machine classes to support other types of simulation and to support running on quantum hardware. Allowing the algorithm to stay constant while varying the underlying machine implementation makes it easy to test and debug an algorithm in simulation and then run it on real hardware with confidence that the algorithm hasn't changed.

Simulator	Class	Namespace	Description
Full state simulator	QuantumSimulator	Microsoft.Quantum.Simulation.Simulators	Runs and debugs quantum algorithms, and is limited to about 30 qubits.
Sparse simulator	SparseSimulator	Microsoft.Quantum.Simulation.Simulators	Simulates quantum algorithms with sparse states, small number of states in superposition.
Trace-based resource estimator	QCTraceSimulator	Microsoft.Quantum.Simulation.Simulators	Runs advanced analysis of resources consumptions for the algorithm's entire call-graph, and supports thousands of qubits.
Toffoli simulator	ToffoliSimulator	Microsoft.Quantum.Simulation.Simulators	Simulates quantum algorithms that are limited to X, CNOT, and multi-controlled X quantum operations, and supports million of qubits.
Noise simulator	OpenSystemsSimulator	Microsoft.Quantum.Simulation.Simulators	Simulates quantum algorithms under the presence of noise, and also the stabilizer representation (also known as CHP simulation) of quantum algorithms.

Next steps

For details about how to invoke target machines for Q# programs in different environments, see Ways to run a Q# program.