Beating the quantum limit in SIS mixers
The 2LO (double local oscillator) mixer is analyzed in the low-LO-power limit for a perfect SIS (superconductor-insulator-superconductor) diode. It is shown that a 2LO SIS mixer can beat the noise performance of a one-LO mixer by a factor of two. It is suggested that even lower noise is possible with an SIS when operated in some other way. >