The Dynamical Casimir Effect as a Photon Budget: Yield per Cycle in a Modulated Superconducting Cavity

When a boundary moves, or when a circuit mimics a moving boundary quickly enough, the vacuum inside a cavity responds by producing real photons, an effect predicted in 1970 and observed in superconducting circuits in 2011. This paper treats the effect as a budget: for modulation frequencies from five to twenty gigahertz and fractional depth changes from five to fifteen percent, it computes the pairs produced per cycle in a stated order-unity model, the resulting pair flux, and the radiated power. The best tabulated case reaches a pair flux of 2.036e+08 per second, of order a femtowatt of microwave power. The budget's lesson is double. The effect is real and detectable because cryogenic detectors count individual microwave photons; and the energies involved, tens of micro-electronvolts per photon, lie just above the milli-electronvolt scale of the surviving vacuum density, making modulated cavities one of the few laboratory systems whose vacuum physics operates anywhere near that scale. All values are computed from the stated model, not measured.