According to Official Guinness Records,
In May 2010 a team from the UNSW Centre for Quantum Computer Technology (Australia) and the University of Wisconsin-Madison (USA) announced their creation of an experimental transistor consisting of a quantum dot within a crystal of silicon. Measuring just 4 nm across, the transistor is made from 7 atoms of phosphorus and is around 10 times smaller than the smallest version used in commercial applications.
Scientists used a scanning tunnelling microscope to manipulate the atoms one at a time to create a transistor that is only four nanometres wide (compared to conventional transistors of about 40 nanometres width). Whilst other researchers have demonstrated devices only two atoms wide, the quantum dot transistor created here offers the first practical demonstration that a real device can be built providing a leap forward in computing speed. This device also opens the possibilities for small devices that can store truly vast amounts of information.
For a complete list of 2010 records, please visit 2010 Guinness Records in Australia.