  Precision measurements using traditional heterodyne readout suffer a 3dB
quantum noise penalty compared with homodyne readout. The extra noise is caused
by the quantum fluctuations in the image vacuum. We propose a two-carrier
gravitational-wave detector design that evades the 3dB quantum penalty of
heterodyne readout. We further propose a new way of realising
frequency-dependent squeezing utilising two-mode squeezing in our scheme. It
naturally achieves more precise audio frequency signal measurements with radio
frequency squeezing. In addition, the detector is compatible with other quantum
nondemolition techniques.
