The sub-quantum transporter was a flawed technology invented by Emory Erickson and studied by the Vulcan Science Academy. It was intended to be the replacement for the transporter used in the mid-22nd century. The sub-quantum transporter would beam an object or person from planet-to-planet, or any other distance, since the device had unlimited range. The system also required much less power to operate.
Erickson confessed in 2154, that even during the initial testing in 2139, he knew the sub-quantum transporter was a fundamentally flawed concept to begin with and would never deliver what it promised. Several men and women who had volunteered to test it were lost. Among these volunteers was his own son, Quinn. Erickson himself was left wheelchair bound.
In 2154, Erickson claimed he had made a breakthrough in his research. Starfleet approved new testing of the technology and Enterprise NX-01 was used to carry out the experiment. The sub-quantum transporter successfully beamed a probe 40,000 kilometers away, a distance never before achieved using traditional transporter technology. There however was no actual breakthrough. Erickson was only using the test as a ruse to gain access to the Enterprise's powerful transporter system in order to attempt a rescue of Quinn's transporter pattern, lost fifteen years earlier in the subspace node of The Barrens. (ENT: "Daedalus")