Characterization of a low noise microwave receiver for the detection of vacuum photons

In this work we present measurements of the sensitivity of a low noise microwave receiver developed with the aim to detect a feeble quantum electrodynamics effect known as dynamical Casimir effect. We study the performance of the receiver when it is connected to a transmission line ending with an antenna coupled to a resonant microwave cavity. The noise temperature of the receiver is measured with the method of the variable temperature load resistor. The noise generated by the cavity is measured in a similar way. An equivalent input noise of ( 2.0 ± 0.2 ) × 10 - 22 W / Hz is measured at the receiver input. This is equivalent to a sensitivity of approximately 100 photons, well below the expected signal from the quantum vacuum photons.