Optimal Impedance Matching and Quantum Limits of Electromagnetic Axion and Hidden-Photon Dark Matter Searches

Understand

For the first time, we determine the properties of the optimal single-moded, linear, passive search for electromagnetic coupling to axion and hidden-photon dark matter, subject to the Standard Quantum Limit on phase-insensitive amplification.

• We establish the parameters that must be considered to determine the optimal search: the impedance match to dark matter; receiver frequency-response and tuning; irreducible noise sources; and prior information on the dark-matter signal.
• Using complex-power flow equations, we identify two categories of coupling to the dark-matter signal: radiative and reactive.
• We motivate a focus on single-moded reactive couplings, as receivers using solely radiative couplings are limited in sensitivity by mismatch with the dark-matter source impedance.