Detection Prospects of Millicharged Dark Matter in Unconventional Interferometer

We propose a novel idea to discover millicharged particles (mCPs) captured by the earth during its existence. It has been demonstrated that the mCPs accumulation inside the earth leads to the enhancement of its number density much larger than the corresponding virial density. We propose to utilize an unconventional laser interferometer to probe these earth-bound mCPs through the detection of the photons's phase shift. We demonstrate that, for mCPs mass in the range between $1$ GeV to $10^{12}$ GeV, the sensitivity of probing their fractional electric charge $\epsilon$ could reach as low as $10^{-12}$ to $10^{-6}$ provided that mCPs number density is greater than $1~\text{cm}^{-3}$.