Thermal Logic Gates

Information processing in the world's computers is mostly carried out in compact electronic devices, which use the flow of electrons both to carry and control information. There are, however, other potential information carriers, such as photons, which are parcels of light. Indeed a major industry, photonics, has developed around the sending of messages encoded in pulsed light.

Heat pulses, or phonons, rippling through a crystal might also become a major carrier, says Baowen Li of the National University of Singapore (phylibw@nus.edu.sg). Li, with his colleague Lei Wang, have now shown how circuitry could use heat---energy already present in abundance in electronic devices---to carry and process information.

They suggest that thermal transistors (also proposed by Li's group in Applied Physics Letters, 3 April 2006) could be combined into all the type of logic gates---such as OR, AND, NOT, etc.-used in conventional processors and that therefore a thermal computer, one that manipulates heat on the microscopic level, should be possible.

Given the fact that a solid state thermal rectifier has been demonstrated experimentally in nanotubes by a group at UC Berkeley (Chang et al., Science, 17 November 2006) only a few years after the theoretical proposal of "thermal diode," the heat analog of an electrical diode which would oblige heat to flow preferentially in one direction (Li et al, Physical Review Letters, 29 October 2004). Li is confident that thermal devices can be successfully realized in the foreseeable future. (Wang and Li, Physical Review Letters, upcoming article