  We develop energy efficient, continuous microwave schemes to couple electron
and nuclear spins, using phase or amplitude modulation to bridge their
frequency difference. These controls have promising applications in biological
systems, where microwave power should be limited, as well as in situations with
high Larmor frequencies due to large magnetic fields and nuclear magnetic
moments. These include nanoscale NMR where high magnetic fields achieves
enhanced thermal nuclear polarisation and larger chemical shifts. Our controls
are also suitable for quantum information processors and nuclear polarisation
schemes.
