Determinism
MENOS is deterministic by design: the same circuit, options and seed produce the same counts and the same plan.
What is guaranteed
| Quantity | Deterministic? |
|---|---|
| Counts, for a given seed | Yes, bit for bit |
| The chosen plan (strategy and engines) | Yes, because it depends only on the circuit and the request |
| Statevector and expectation value | Yes (exact computations) |
| Counts on CPU versus CUDA, same seed | Identical, by construction |
Wall-clock fields (execute_s, sample_s) | No: they are measurements |
| Backend choice and time-budget feasibility | Depend on calibrated speed, so on the machine |
The one place a plan can differ between machines is the choice of CPU or CUDA, and the time-budget check, because both compare measured seconds. The choice of algorithm never depends on timing.
Seeds
python
from qiskit import QuantumCircuit
from menos.qiskit import MENOSBackend
qc = QuantumCircuit(2, 2)
qc.h(0)
qc.h(1)
qc.measure([0, 1], [0, 1])
backend = MENOSBackend()
first = backend.run(qc, shots=300, seed_simulator=2024).result().get_counts()
second = backend.run(qc, shots=300, seed_simulator=2024).result().get_counts()
different = backend.run(qc, shots=300, seed_simulator=2025).result().get_counts()
assert first == second
assert first != different| Interface | Default seed |
|---|---|
MENOSBackend.run | A fresh random seed per call, recorded in results[0].seed_simulator |
Native RunOptions.seed | 0 |
If you want reproducibility through MENOSBackend, pass seed_simulator explicitly.
How it is achieved
- One seeded pseudo-random generator is used by every engine, rather than the standard library's distributions, whose output can differ between implementations.
- Sub-streams for separate regions come from a fixed mixing of the job seed.
- Device kernels are built so that statevectors are bitwise identical to the CPU's, and counts are sampled on the host from that state.
- A replanned run is identical to running its final plan from a cold start.
A scope statement
The guarantee is the design invariant; what has been verified is Linux on x86-64. Identical results on other platforms are intended and untested. See Supported Platforms.