Filter-function control.
Measure the noise, then dodge it — signed.
Measure the noise a qubit feels, then shape its pulses to avoid it.
Real qubits are limited by correlated, low-frequency noise — 1/f dephasing above all. A
frequency-domain answer is the filter function: a control's first-order sensitivity F(ω) to
dephasing, so the coherence decay is the overlap χ = (1/π)∫ S(ω)F(ω)/ω² dω of the noise
spectrum with the filter. Two matched capabilities fall out of that one integral — and both run
entirely offline against a model, so they are fully deterministic and receiptable.
Spectroscopy reconstructs the hidden noise S(ω) from a bank of
dynamical-decoupling filters; robust control reshapes a DD sequence so its filter's stopband
sits over that noise. Everything is pure integer arithmetic (byte-identical on every machine),
and each seals a signed wai.quantum.calibration receipt — the robust one binds the exact
PSD hash it was hardened against. Scope: a clean first-order dephasing model on a
simulated device; what is not approximate is the reproducibility of the DSP.
Noise spectroscopy · recover S(ω)
Filter-function robust control · dodge the PSD
The matched pair — a signed PSD, and a pulse that provably avoids it
The spectroscopy panel treats a bank of CPMG sequences as narrow-band filters at different centre
frequencies; the coherence each retains under the hidden spectrum measures S(ω) there,
and a Richardson–Lucy deconvolution (positivity-preserving) reconstructs the whole PSD — recovering
a hidden 1/f-plus-bump spectrum it was never told. The robust-control panel takes a PSD and reshapes
a DD sequence's pulse timing so its filter's passband moves off the noise: equal-spaced CPMG
has its passband sitting right on the bump (large overlap, low coherence), and the optimiser slides
the pulses until the filter notches the bump out — a large coherence gain. Both run with
no hardware front-end at all, hash identically on every machine, and carry a
signed receipt; the robust receipt binds the PSD hash, so "this pulse is robust
against that spectrum" is a checkable claim, not an assertion.
Where it lives. The wai.quantum.calibration receipt these panels seal is in
the standard (the quantum-ops extension). The spectroscopy and robust-control engine is reference
code in the open-standards repo, Apache-2.0.
Energy: not metered. Receipts sealed in this tab carry a placeholder joule value, so the page shows none.