  Gravitational wave detectors (GWDs), which have brought about a new era in
astronomy, have reached such a level of maturity that further improvement
necessitates quantum-noise-evading techniques. Numerous proposals to this end
have been discussed in the literature, e.g., invoking frequency-dependent
squeezing or replacing the current Michelson interferometer topology by that of
the quantum speedmeter. Recently, a proposal based on the linking of a standard
interferometer to a negative-mass spin system via entangled light has offered
an unintrusive and small-scale new approach to quantum noise evasion in GWDs
[Phys. Rev. Lett. $\mathbf{121}$, 031101 (2018)]. The solution proposed therein
does not require modifications to the highly refined core optics of the present
GWD design and, when compared to previous proposals, is less prone to losses
and imperfections of the interferometer. In the present article, we refine this
scheme to an extent that the requirements on the auxiliary spin system are
feasible with state-of-the-art implementations. This is accomplished by
matching the effective (rather than intrinsic) susceptibilities of the
interferometer and spin system using the virtual rigidity concept, which, in
terms of implementation, requires only suitable choices of the various
homodyne, probe, and squeezing phases.
