Definition: Apparatus-cutoff interface

An apparatus-cutoff comparison specifies:

1. a full model and a retained model;

2. state encodings and identified output interfaces;

3. paired operations and a declared input class;

4. the experiment and resource budgets;

5. a comparison certificate, for example

   $$d_{\mathrm{TV}}({\mu }_{\mathrm{full}},{\mu }_{\mathrm{retained}})\le \delta .$$

A spectral cutoff must have a finite-rank retained space with a finite qubit encoding before it is an Enter configuration. Spectral projection alone does not guarantee finite rank. A certificate for one prepared input law is not automatically a uniform channel or reference-preserving certificate.