Quantum Virtual Machine (QVM)

A Python quantum computing toolkit that works like a classical toolchain: install it, point it at a circuit, run it. QVM ingests quantum programs (OpenQASM 3.0 / 2.0 / JSON / Qiskit / Cirq), transpiles them onto hardware topologies, simulates them exactly, and exports them anywhere else — through one canonical Intermediate Representation.

QASM 3 ──┐                              ┌──► QVM Statevector / MPS simulation
QASM 2 ──┤   ┌────────────────┐         ├──► QVM Transpiler (Greedy / SABRE routing)
JSON  ───┼──►│    QVM IR      │─────────┼──► Qiskit  (export · Aer backend)
Qiskit ──┘   │  (the pivot)   │         └──► Cirq     (export · Cirq simulator)
Cirq  ──────►└────────────────┘

v0.4 highlights

• Installable package (pip install) with a qvm CLI entry point
• Strict framework interop: unsupported operations raise, they are never silently dropped
• Full bidirectional gate coverage between QVM ↔ Qiskit ↔ Cirq (22-gate vocabulary)
• Domain exception hierarchy (QVMError root) for reliable error handling
• In-place O(2^N) statevector kernels, configurable execution budgets, cached QASM3 parser

---

Installation

Requires Python ≥ 3.9. The core depends only on numpy and lark; everything else is opt-in:

pip install quantum-virtual-machine              # lean core: parse, transpile, simulate
pip install "quantum-virtual-machine[qiskit]"    # + Qiskit & Aer interop
pip install "quantum-virtual-machine[cirq]"      # + Cirq interop
pip install "quantum-virtual-machine[viz]"       # + matplotlib visualizations
pip install "quantum-virtual-machine[server]"    # + FastAPI dashboard stack
pip install "quantum-virtual-machine[dev]"       # + pytest and dev tooling

From source (development):

git clone https://github.com/qayumXD/quantum-virtual-machine.git
cd quantum-virtual-machine
pip install -e ".[dev]"

Optional backends degrade gracefully: calling an interop API without the matching extra raises MissingBackendError with the exact pip install command to fix it.

---

Quickstart

CLI

qvm circuit.qasm                                   # simulate a QASM file
qvm circuit.json --nqubits 4                       # simulate a JSON gate list
qvm bell.qasm --shots 1024 --seed 42               # shot-based sampling
qvm bell.qasm --transpile --routing sabre          # route onto linear topology
qvm bell.qasm --device fake_5q                     # hardware noise profile
qvm vqe_circuit.json --nqubits 2 --expectation ZZ  # Pauli expectation value

Python API

from qvm.parser import OpenQASM2Parser
from qvm.transpiler import Transpiler
from qvm.simulator import Simulator
from qvm.architecture import get_linear_architecture

qc = OpenQASM2Parser.parse(open("examples/bell_state.qasm").read())

arch = get_linear_architecture(qc.num_qubits)
qc = Transpiler(arch, strategy="sabre").transpile(qc)

state, classical_memory = Simulator().simulate(qc)
print((abs(state) ** 2).round(3))

Framework bridge

import cirq, qiskit
from qvm.ir import QuantumCircuit

circuit = cirq.Circuit(cirq.H(cirq.LineQubit(0)), cirq.CNOT.on(cirq.LineQubit(0), cirq.LineQubit(1)))
qk_circuit = QuantumCircuit.cirq_to_qiskit(circuit)   # Cirq → QVM IR → Qiskit

---

Framework interoperability

All conversions go through the QVM IR pivot (N+M converters instead of N×M). The interop layer is governed by two guarantees:

1. No silent drops. Every operation either converts faithfully or raises UnsupportedGateError naming the offending gate. A conversion that returns means the returned circuit is your circuit.
2. Physical equivalence. Exported circuits reproduce QVM's measurement probability distributions (validated by a triple-engine test suite: QVM vs Qiskit vs Cirq).

Supported vocabulary:

Class	Gates
1-qubit, no parameters	h, x, y, z, s, sdg, t, tdg, sx, sxdg, id
1-qubit, 1 angle	rx(θ), ry(θ), rz(θ), p(λ)
2-qubit, no parameters	cx, cz, swap
2-qubit, 1 angle	rxx(θ), rzz(θ), cp(λ)
3-qubit	ccx
Ancillary	measure, barrier, delay

Notes:

• Parameters: symbolic parameters survive conversion (Qiskit Parameter ↔ QVM Parameter ↔ Cirq sympy symbols). Fully-bound expressions export as floats; partially-bound ones raise QVMConversionError until you call bind_parameters().
• Measurements: Cirq keys use the canonical "register[index]" format; legacy tuple-string keys are still parsed on import.
• Global phase is not represented in the IR and is therefore not preserved (physically unobservable, same convention as OpenQASM).
• Anything outside the vocabulary — control flow, arbitrary unitaries, exotic gates — fails loudly with a message listing the supported set.

Full details: docs/guides/INTEROP.md

---

Error handling

Every QVM error derives from one base class, so callers can catch broadly or narrowly:

from qvm.exceptions import (
    QVMError,               # root
    QVMParseError,          # syntax / grammar failures        (ValueError)
    QVMCompilationError,    # routing / decomposition / conversion failures
    UnsupportedGateError,   # gate outside a subsystem's vocabulary
    QVMConversionError,     # unfaithful-or-impossible format conversion
    MissingBackendError,    # optional Qiskit/Cirq extra not installed (ImportError)
    QVMRuntimeError,        # simulation failures               (RuntimeError)
    QVMResourceLimitError,  # op-budget breaches                (RuntimeError)
)

Concrete classes also inherit the built-in shown in parentheses, so existing except ValueError / except RuntimeError code keeps working during migration.

Validation is eager: malformed arities (cx on one qubit), measurements into undeclared registers, and unknown gates all fail at circuit-construction time — never mid-simulation.

---

Simulation engines

Engine	Use case	Notes
Simulator (statevector)	Exact amplitudes, N ≲ 12–16	In-place tensor-stride kernels, full classical memory + label/jump control flow, stochastic Kraus noise trajectories
MPSSimulator	Low-entanglement circuits, 20+ qubits	Bond-dimension-truncated SVD evolution

Noise modeling supports depolarizing, amplitude damping, and phase damping channels plus device profiles (fake_5q, fake_7q, ideal). For a candid assessment of scaling limits beyond this range, see docs/production_readiness_analysis.md.

---

Testing

pytest                                        # whole unit + interop suite
pytest tests/test_interop_roundtrip.py -v     # interop guarantees (triple-engine equivalence)
python -m benchmarks.run_audit --all          # 19-algorithm audit corpus (QASM/Qiskit/Cirq/VQE/QAOA)

The interop suite verifies probability agreement across QVM, Qiskit, and Cirq for every gate in the vocabulary, round-trip structural preservation, and that unsupported inputs raise rather than corrupt. The audit corpus runs textbook-to-industry algorithms end-to-end and cross-validates against native simulators — see docs/reports/algorithm_audit_2026-08-24.md.

---

Project layout

quantum-virtual-machine/
├── pyproject.toml            # packaging, extras, console script
├── src/qvm/                  # the installable `qvm` package
│   ├── ir.py                 # QuantumCircuit IR + framework converters
│   ├── parser.py             # QASM 2.0 + JSON ingestion
│   ├── qasm3_parser.py       # OpenQASM 3.0 (Lark LALR, module-cached)
│   ├── transpiler.py         # Greedy / SABRE routing
│   ├── decomposer.py         # gate decomposition passes
│   ├── simulator.py          # dense statevector engine
│   ├── mps_simulator.py      # tensor-network engine
│   ├── noise.py              # Kraus channels & noise models
│   ├── observable.py         # Hamiltonians / Pauli expectations
│   ├── vqe.py / qaoa.py / gradient.py / parameter.py
│   ├── cli.py                # `qvm` command
│   ├── exceptions.py         # domain error hierarchy
│   └── util/export.py        # exporters
├── api/app.py                # optional FastAPI service
├── web/                      # optional Next.js dashboard
├── tests/                    # pytest suite (incl. interop + stress)
└── docs/                     # design docs, guides, readiness analysis

License

MIT — see distribution metadata.