2015: Francesco Amato builds the first microwave Quantum Tunneling Tag (QTR). This 5.8 GHz tag will scatter a signal over a kilometer across midtown Atlanta, consuming only 23 microWatts in the process.
It started with a simple test question back in 2008 and snowballed into a research program. In 2015, Francesco Amato built and demonstrated the world’s first “quantum tunneling tag” (QTR), which is an antenna terminated in a tunnel diode that, when biased with minimal DC voltage, acts as a microwave reflection amplifier. The most dramatic display of the power of a QTR came when Francesco scattered a detectable signal 1.2 km across midtown Atlanta while consuming only 23 microWatts of power.
Fun fact #1: The 1.2 km measurement used a QTR mounted on the 10-story swimming pool deck of ECE accountant Siri Melkote, who was kind enough to allow access to her condo.
Fun fact #2: Tunnel diodes are, conceptually, on of the simplest semiconductor devices you can imagine: just and over-doped PN-junction. Leo Esaki won the Nobel Prize for their invention back in 1973. However, there are very few mainstream applications for the devices, meaning that the GTPG pays nearly $50 per device to construct its RF tags!