  We propose high-frequency gravitational wave (GW) detectors with Rydberg
atoms. Rydberg atoms are sensitive detectors of electric fields. By setting up
a constant magnetic field, a weak electric field is generated upon the arrival
of GWs. The weak electric field signal is then detected by an
electromagnetically induced transparency (EIT) in the system of the Rydberg
atoms. Recently, the sensitivity of the Rydberg atoms is further improved by
combining superheterodyne detection method. Hence, even the weak signal
generated by the GWs turns out to be detectable. We calculate the amplitude of
Rabi frequency of the Rydberg atoms induced by the GWs and show that the
sensitivity of the Rydberg atoms becomes maximum when the size of the Rydberg
atoms is close to the wavelength of GWs. As an example, we evaluate the
sensitivity of the GW detector with Rubidium Rydberg atoms and find that the
detector can probe GWs with a frequency 26.4 GHz and an amplitude approximately
around $10^{20}$. We argue that the sensitivity can be further enhanced by
exploiting entangled atoms.
