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Quantum Reservoir Computing

This page defines the named quantum reservoir computing (QRC) surface in this repository and its classical baseline boundary.

Production Surfaces

The QRC surface is split across two bounded modules:

  • scpn_quantum_control.applications.quantum_reservoir maps classical inputs through Kuramoto-XY Hamiltonian evolution and Pauli expectation features, then fits a ridge readout.
  • scpn_quantum_control.analysis.qrc_phase_detector uses exact dense ground-state Pauli features as a small-system phase-detector reference.

QWC-4.3 adds the named comparison surface:

import numpy as np

from scpn_quantum_control.applications import compare_quantum_reservoir_to_esn
from scpn_quantum_control.bridge.knm_hamiltonian import build_knm_paper27

rng = np.random.default_rng(42)
X_train = rng.uniform(size=(10, 3))
y_train = np.sin(2.0 * X_train[:, 0]) + 0.25 * X_train[:, 1]
K = build_knm_paper27(L=3)

comparison = compare_quantum_reservoir_to_esn(
    X_train,
    y_train,
    K,
    alpha=0.5,
    max_weight=1,
    seed=5,
)

By default the classical echo-state network (ESN) uses the same number of features as the QRC feature map. Callers can set reservoir_size explicitly when they need a deliberately unmatched-capacity comparison.

Classical Baseline

classical_esn_feature_matrix implements a deterministic ESN reference:

  • seeded input and recurrent weights;
  • recurrent matrix rescaled to the requested spectral radius;
  • leaky state update;
  • ridge readout through classical_esn_ridge_regression.

The ESN exists to keep QRC claims honest. A QRC result is not promoted by this repository unless it is compared against the classical baseline at a stated feature count and task.

Functional Evidence

Local non-isolated smoke evidence on 2026-07-08, run on the workstation while other repository work was active:

Operation System Time Output
compare_quantum_reservoir_to_esn(10 samples) 3 qubits, 9/9 matched features 48.5 ms QRC MSE=0.018606, ESN MSE=0.037680

This is functional evidence for wiring and bounded task behaviour. It is not an isolated-core production benchmark.

Explicit Boundaries

  • The QRC feature map is exact-statevector and small-system bounded.
  • The phase detector is an exact dense reference, not a scalable reservoir simulator.
  • The ESN baseline is a deterministic NumPy reference comparator, not an accelerated service path.
  • No hardware-QRC advantage claim is made here.
  • No broad time-series benchmark claim is made until a preregistered benchmark beats the ESN baseline at matched task and feature count.