FlagQuantum Compiler QSteed

flagquantum-compiler-qsteed is an independently installed circuit compiler plugin for FlagQuantum. It translates FlagQuantum CircuitIR to a PyQuafu QuantumCircuit, invokes QSteed's real transpiler, and translates the compiled circuit back to CircuitIR.

The first release deliberately supports one closed, testable slice:

• static h, x, rx, ry, rz, and cx instructions with numeric angles;
• basis lowering to a selected subset of those gates, with topology routing on the fixed six-gate basis;
• an optional undirected coupling map over the circuit's existing wires;
• deterministic QSteed basis lowering and SABRE routing;
• restoration of QSteed's final physical layout to FlagQuantum's logical wire order.
• Quafu calibration targets with automatic or explicitly ordered physical subgraph selection and a target_qubits result; physical identifiers never replace logical QASM wires.

Measurements, observables, symbolic parameters, custom matrices, dynamic operations, additional target fields, and larger physical topologies are rejected. There is no compiler substitution or fallback. Omitting coupling_map explicitly requests basis compilation without topology routing. For a Quafu chip_info target, omitting target_qubits lets QSteed choose the subgraph. Supplying it locks the logical-to-physical order after existence, uniqueness, and connectivity validation; the plugin never substitutes another mapping.

Installation

This release candidate requires FlagQuantum >=0.2,<0.3 and the verified QSteed build 0.2.3+quafu.sqc. It is not yet a one-command PyPI installation: FlagQuantum 0.2 and this QSteed build must be installed first. PyPI QSteed 0.2.2 is not a supported substitute. Python 3.12 was used for the release checks; the declared Python 3.10–3.12 range still needs a full compatibility matrix.

From this repository, after installing a compatible FlagQuantum checkout:

python -m pip install -r requirements-qsteed.txt
python -m pip install -e ".[test]"
python -m pytest -q

The dependency file pins the verified upstream commit. The wheel declares its exact package version without embedding a Git URL. Once the plugin is published, users with both prerequisites already installed can use python -m pip install flagquantum-compiler-qsteed==0.1.0.

Compile a circuit

This offline example needs no provider credentials and submits no hardware job:

import flagquantum as fq

circuit = fq.Circuit(3).h(0).cx(0, 2)
compiled = fq.compile(
    circuit,
    compiler="qsteed",
    target={
        "basis_gates": ("h", "x", "rx", "ry", "rz", "cx"),
        "coupling_map": ((0, 1), (1, 2)),
    },
)
print(compiled.instructions)

See release preparation for publication prerequisites and artifact checks.

Advanced extension lifecycle

from flagquantum.ecosystem.extensions import (
    CapabilityRequest,
    ExtensionConfig,
    discover_extensions,
)

import flagquantum as fq

source_ir = fq.Circuit(3).h(0).cx(0, 2).to_ir()
registry = discover_extensions("compiler")
handle = registry.negotiate(
    "compiler",
    "qsteed",
    CapabilityRequest(required=frozenset({"circuit_ir"})),
)
handle.start(ExtensionConfig())
try:
    compiled = handle.invoke(
        "compile",
        source_ir,
        target={
            "basis_gates": ("h", "x", "rx", "ry", "rz", "cx"),
            "coupling_map": ((0, 1), (1, 2)),
        },
    )
finally:
    handle.close()

QSteed treats the coupling graph as bidirectional in this compiler path. The plugin therefore validates two-wire instructions against undirected edges.