Gravitational_Wave_Detection_via_Orthogonal_Dual_Cavity_Interferometry

We propose a scalable resonant detector architecture for gravitational waves (GW) based on a superconducting microwave bridge interferometer. The fundamental unit — the Orthogonal SRF Bridge Interferometer (OSBI, hereafter “the bridge”) — consists of two orthogonal Superconducting Radio Frequency (SRF) cavities fed by a balanced Magic-Tee splitter from a cryogenic sapphire oscillator (CSO). The entire structure is treated as a single coupled super-cavity supporting symmetric and antisymmetric eigenmodes. Operating in the quasi-static parametric regime (fgw ≪ ∆f = f0/Q), the gravitational wave acts as a slow boundary deformation that differentially detunes the two arms via the Slater Perturbation Theorem, without requiring resonance between the GW frequency and the cavity modes. The accumulated differential phase ∆ϕ = Q · h follows from integration over the photon lifetime τ = Q/ω0, and linear voltage sensitivity (V ∝ h) is achieved through homodyne detection with the CSO carrier as the built-in local oscillator. The instrument obeys a fundamental Gain-Bandwidth Product: ∆ϕ · ∆f = f0 · h, meaning sensitivity and bandwidth cannot be simultaneously maximised. By tuning Q and f0, the same architecture covers multiple science targets: a high-Q configuration (Q ∼ 1010) achieves h ∼ 10−22/√Hz in a 1 Hz band targeting the primordial stochastic GW background; a medium-Q configuration (Q ∼ 106) opens the kHz–MHz band for post-merger neutron stars; and a low-Q configuration (Q ∼ 103) covers the MHz–GHz band for exotic sources and primordial black hole mergers. The detection philosophy is grounded in the Dark-Port Compensation Principle: just as cosmological redshift is visible only to an observer whose spectral reference lies outside the perturbed metric, the GW signal is readable only at the recombination dark port. The single-bridge unit extends to a tri-bridge array of three orthogonal unit cells sharing a single cryogenic enclosure with three mutually orthogonal CSOs, enabling full three-dimensional GW strain tensor reconstruction from a single compact instrument.