Backends and verification

Quon separates the shared frontend from target-specific artifact generation. Fixed gate-model targets produce OpenQASM 3. Reconfigurable neutral-atom targets produce schedule JSON and resource reports. The Qiskit Aer bridge verifies the OpenQASM path locally without a hardware account.

Fixed gate-model targets

A fixed BackendTarget JSON file records the gate-model constraints associated with a compilation:

• id names the target in diagnostics and metrics.
• num_qubits sets the available physical qubits.
• topology.edges lists directly connected qubit pairs. Routing inserts swaps when a two-qubit operation is not adjacent.
• native_gates lists the OpenQASM gate names the target accepts. The compiler decomposes unsupported operations before emission and rejects unknown gate names.
• noise can record gate fidelity, T1/T2 times, and readout error. T1 values can inform scheduling; the values are target metadata rather than an Aer simulator noise model.
• meas_latency_us, supports_mid_circuit_meas, and supports_feed_forward record measurement and dynamic-circuit capabilities.

The optional top-level "kind": "fixed" makes the architecture family explicit. A descriptor without kind is read as a fixed target for backward compatibility. See backend/tests/fixtures/device_5q.json for a complete example.

Inspect a descriptor:

cargo run -p quonc -- \
  --target backend/tests/fixtures/device_5q.json \
  --print-target

Emit OpenQASM 3

Compile a Bell-state program for the five-qubit fixture:

cargo run -p quonc -- \
  test/verify/bell.qn \
  --target backend/tests/fixtures/device_5q.json \
  --emit-qasm

With no --target, quonc uses the built-in generic_openqasm target: 64 all-to-all qubits, the standard OpenQASM gate set, and no device noise data.

Neutral-atom targets

A neutral_atom_reconfigurable descriptor models a different architecture family: zones, array geometry, AOD movement, Rydberg interactions, timing, fidelity, and a cost model. Quon compiles these targets to schedule and resource artifacts rather than OpenQASM.

cargo run -p quonc -- test/na/qaoa_graph.qn \
  --target targets/neutral_atom/generic_rna_v0.json \
  --emit-na-schedule schedule.json \
  --emit-na-graph graph.dot \
  --emit-resource-report report.md \
  --resource-report-format markdown

The neutral-atom path extracts the interaction graph, schedules entangling layers, chooses a movement backend, optionally compacts the result, and reports timing/resource estimates.

--emit-resource-report is a compiler analytic artifact (schedule metrics, QEC metadata, error_budget = rate × count). Sampled logical failures from python/quon_qec_sinter.py stay in a separate CSV. An optional labeled join CSV from the #254 ablation harness is allowed for comparisons only — it does not replace the separate Sinter CSV or mutate the report (ADR-0020). Neither artifact is a threshold claim.

--emit-na-schedule writes a versioned visualization envelope (kind: na_schedule_view) with zones, layout, metrics, and schedule layers — a debug view, not the canonical schedule IR (--emit-na-mlir). --emit-na-graph writes Graphviz DOT for the interaction graph.

Render frames / the graph with matplotlib + Graphviz (no HTML):

pip install -r python/requirements-viz.txt
python python/visualize_na_schedule.py schedule.json --graph graph.dot \
  -o /tmp/na-viz --format svg

meta.na_placer / meta.na_backend in the schedule JSON are reserved so a future before/after (routing-agnostic vs routing-aware) comparison can share axes without a schema bump.

Useful neutral-atom options:

• --na-backend zoned uses zoned architecture scheduling (default placer is routing-agnostic / ZAC-style; --na-placer routing-aware selects the RAP-style search).
• --na-backend flat uses the flat AOD movement path.
• --na-placer routing-agnostic or --na-placer routing-aware selects the zoned placement mode.
• --na-placement row-major selects the flat AOD placement strategy.
• --no-na-compact leaves the schedule uncompacted for inspection.

See the neutral-atom architecture model for the target schema, assumptions, and citations.

Run OpenQASM output on Aer

Install the optional verification dependencies and build the compiler:

just setup-python
source .venv/bin/activate
cargo build -p quonc

No QUONC export is needed. After cargo build, the Aer bridge auto-discovers the local compiler binary, probing target/release/quonc then target/debug/quonc before falling back to quonc on PATH (#375). Set QUONC explicitly only to override that order — for example, to pin a binary built with non-default features.

python/quon_aer.py accepts either Quon source or OpenQASM on standard input — one copy-paste command from source to Aer counts:

python python/quon_aer.py test/verify/bell.qn --shots 4096 --seed 1234

Or pipe emitted QASM through a constrained target:

cargo run -p quonc -- test/verify/bell.qn \
  --target backend/tests/fixtures/device_5q.json \
  --emit-qasm |
  python python/quon_aer.py --shots 4096 --seed 1234

The bridge imports the emitted OpenQASM and runs an ideal AerSimulator. --seed makes sampling reproducible. The printed counts are raw simulation results, not live-hardware performance estimates. When a required Python package is missing, the error names the active Python executable and prints a ready-to-run install command using the project .venv when one exists.

Run reference verifiers

The scripts in test/verify/ add assertions to compilation and simulation. Run all same-stem .qn/.py cases — the compiler binary is auto-discovered, so no QUONC prefix is required after a build:

bash test/verify/run_e2e.sh

Or run one case by stem:

bash test/verify/run_e2e.sh bell

The reference oracles cover Bell, teleportation, Bernstein-Vazirani, Grover, QFT, Ising, QAOA, dense spin-glass QAOA, and Shor’s quantum kernel.

The routing verifier checks constrained fixed targets against the all-to-all baseline:

python test/verify/routing.py

<<<<<<< HEAD Set QUONC only when you need to point at a specific binary instead of the auto-discovered one.

Diagnostic catalog

When a backend target or emission flag is rejected, the diagnostic catalog lists every target-descriptor and emission error with its cause and repair.

4b74572 (docs: create task-oriented Quon diagnostic catalog (#381))