QVm

QVM, or Quantum Virtual Machine, is a software-based simulator of a quantum processor that runs on classical hardware. It is used to develop, test, and debug quantum programs before execution on real quantum hardware. In the Rigetti Computing ecosystem, the QVM executes programs written in Quil, the company's quantum instruction language, via the PyQuil library or the Quil compiler.

The QVM can simulate quantum circuits by propagating either state vectors or density matrices, depending on the chosen mode. It supports common quantum operations such as multi-qubit gates and measurements, and can model classical control flow as specified by Quil. To provide more realistic testing conditions, the QVM can incorporate noise models that emulate decoherence, gate errors, and readout imperfections.

Users typically run the QVM locally or on cloud platforms offered by the service, obtaining measurement results by taking multiple shots to estimate output distributions and expectation values. This makes the QVM valuable for algorithm development, verification, and debugging without access to a physical quantum processor.

Limitations arise from the fundamental scaling of quantum systems: simulating n qubits on a classical computer requires resources that grow exponentially with n. Consequently, the QVM is most suitable for circuits with a modest number of qubits, with practical use often spanning tens of qubits on capable hardware. Nevertheless, it remains a central tool for prototyping quantum programs and testing how they perform under ideal or noisy conditions.

See also: QPU, Quil, PyQuil, Forest (Rigetti).