Scalable Spin Amplification with a Gain over a Hundred
  We propose a scalable and practical implementation of spin amplification which does not require individual addressing nor a specially tailored spin network. We have demonstrated a gain of 140 in a solid-state nuclear spin system of which the spin polarization has been increased to 0.12 using dynamic nuclear polarization with photoexcited triplet electron spins. Spin amplification scalable to a higher gain opens the door to the single spin measurement for a readout of quantum computers as well as practical applications of nuclear magnetic resonance (NMR) spectroscopy to infinitesimal samples which have been concealed by thermal noise. 
Makoto Negoro, Kenichiro Tateishi, Akinori Kagawa, Masahiro Kitagawa
quant-ph