  Quantum optical states are fragile and can become corrupted when passed
through a lossy communication channel. Unlike for classical signals, optical
amplifiers cannot be used to recover quantum signals. Quantum repeaters have
been proposed as a way of reducing errors and hence increasing the range of
quantum communications. Current protocols target specific discrete encodings,
for example quantum bits encoded on the polarization of single photons. We
introduce a more general approach that can reduce the effect of loss on any
quantum optical encoding, including those based on continuous variables such as
the field amplitudes. We show that in principle the protocol incurs a resource
cost that scales polynomially with distance. We analyse the simplest
implementation and find that whilst its range is limited it can still achieve
useful improvements in the distance over which quantum entanglement of field
amplitudes can be distributed.
