Nuclear spins in material can be easily controlled with electromagnetic waves. NMR (Nuclear Magnetic Resonance) spectroscopy and MRI (Magnetic Resonance Imaging), which exploit this characteristic of the nuclear spins, are widely used to obtain various information as to chemical compounds and living bodies.However, the signal from a nuclear spin is so faint that the detection requires a huge amount of nuclear spins. The inductive detection, which is the conventional method for NMR spectroscopy and MRI, requires more than a million of nuclear spins. Therefore microscopic samples can not be analyzed. If the information of a nuclear spin is copied to surrounding spins, the signal from the nuclear spin is amplified and the sensitivity can be increased (Figure). This method is called spin amplification. The known implementations require individual addressing to the surrounding spins and have difficulty in making many copies. The demonstrated gain was as low as 4. We have proposed a novel implementation of the spin amplification which enables a large number of copies without individual addressing. We have achieved a gain as high as 140 in a single crystal of an organic compound and measured 140-time amplified NMR spectroscopic signals. The spin amplification of the gain of 140 in conjunction with modern MRFM (Magnetic Resonance Force Microscopy) technology, of which the minimum detectable number of nuclear spins is on the order of 100, enables the detection of a single nuclear spin. Nuclear spins have been extensively studied for a quantum computer, an ultrahigh-speed computer of the future, because it can hold quantum information for a long time. This work opens a door to the utilization of nuclear spins in quantum computers. |
 Instrumentation for spin amplification |