  When performing continuous measurements of position with sensitivity
approaching quantum mechanical limits, one must confront the fundamental
effects of detector back-action. Back-action forces are responsible for the
ultimate limit on continuous position detection, can also be harnessed to cool
the observed structure, and are expected to generate quantum entanglement.
Back-action can also be evaded, allowing measurements with sensitivities that
exceed the standard quantum limit, and potentially allowing for the generation
of quantum squeezed states. We realize a device based on the parametric
coupling between an ultra-low dissipation nanomechanical resonator and a
microwave resonator. Here we demonstrate back-action evading (BAE) detection of
a single quadrature of motion with sensitivity 4 times the quantum zero-point
motion, back-action cooling of the mechanical resonator to n = 12 quanta, and a
parametric mechanical pre-amplification effect which is harnessed to achieve
position resolution a factor 1.3 times quantum zero-point motion.
