Isolation of test masses in the advanced laser interferometric gravitational-wave antennae

We analyze the experimental conditions required for the action of thermal, seismic, and excess noises on the test mass in the advanced LIGO experiment to be smaller than the uncertainty of the coordinate corresponding to the standard quantum limit. It is shown that the contribution of thermal noise can be made small enough if existing low-dissipation materials are used for the suspension. On the other hand, the contribution of excess noise can be large and has to be examined thoroughly.