Qiberis

circuits
ecosystem-member
A backend-agnostic quantum circuit API for Qiskit, Cirq, and PennyLane
Published

June 1, 2026

STATUS · Qiskit Ecosystem Member · Converter · Python interface · MIT license

The problem

Qiskit, Cirq, and PennyLane each have their own circuit objects, gate names, execution APIs — and, less obviously, their own bit-ordering conventions for returned counts. Comparing results across simulators, or writing code that shouldn’t care which one happens to be installed, means re-solving the same translation problem every time.

What Qiberis does

Qiberis defines a circuit once, against a small backend-agnostic intermediate representation, and runs it unmodified on any of three simulators:

from qiberis import Circuit
from qiberis.backends.qiskit_backend import QiskitAerBackend
from qiberis.backends.cirq_backend import CirqSimulatorBackend
from qiberis.backends.pennylane_backend import PennyLaneLightningBackend

circuit = Circuit(3)
circuit.h(0).cx(0, 1).cx(1, 2).measure_all()

for backend_cls in (QiskitAerBackend, CirqSimulatorBackend, PennyLaneLightningBackend):
    backend = backend_cls()
    result = backend.run(circuit, shots=1000)
    print(result)
  • Qiskit Aer — statevector simulation
  • Cirq — Google-ecosystem simulation, for cross-checking gate decompositions
  • PennyLane (lightning.qubit) — for hybrid and variational workflows

Each backend is an optional dependency (pip install -e ".[qiskit]", .[cirq], .[pennylane], or .[all]); the core package — Circuit and Result — has zero hard dependencies, and an adapter you haven’t installed raises a clear ImportError rather than failing silently.

The part that actually breaks most “universal circuit” projects

Qiskit’s native count strings are little-endian — clbit 0 is the rightmost character. Cirq and PennyLane’s qml.counts are naturally ordered with the first wire leftmost. Silently mixing these is the classic way a “backend-agnostic” layer quietly gives wrong answers.

Qiberis’s convention: in every Result.counts key, the leftmost character is always clbit/qubit 0. The Qiskit adapter reverses its native strings to match; Cirq and PennyLane need no adjustment. This is enforced by a dedicated regression test — an asymmetric circuit (X on qubit 0 only) run through all three backends, checked to agree on the same string — not just asserted in a docstring.

Architecture

qiberis/
  circuit.py          # Circuit + Instruction: the backend-agnostic IR
  result.py           # Result: normalized counts/probabilities
  backends/
    base.py           # Backend ABC — one method: run(circuit, shots) -> Result
    qiskit_backend.py
    cirq_backend.py
    pennylane_backend.py
tests/
  test_cross_backend.py  # runs the same circuits on every installed backend
                          # and checks they agree with each other

Supported gates: h, x, y, z, s, t, rx, ry, rz, cx, cz, swap, ccx, barrier, measure. Adding a new backend is: subclass Backend, implement run(), translate Circuit.instructions into the target library’s native object, normalize the output into Qiberis’s bit-ordering convention, then add it to test_cross_backend.py’s BACKENDS list — the existing GHZ, bit-ordering, and cross-agreement tests immediately validate it against the other two.

Roadmap

  • Real hardware backends (IBM Quantum, AWS Braket QPUs) behind the same interface
  • A transpiler/optimization pass operating directly on the IR
  • Parametric circuits — binding parameters without rebuilding the circuit
  • Statevector and expectation-value result modes, not just counts
  • More gates: u, crx/cry/crz, iswap, multi-controlled gates