Optical transistor created from single molecule

By using one laser beam to prepare the quantum state of a single molecule in a controlled fashion, scientists could significantly attenuate or amplify a second laser beam. This mode of operation is identical to that of a conventional transistor, in which electrical potential can be used to modulate a second signal. The researchers used the fact that a molecule's energy is quantised: when laser light strikes a molecule that is in its ground state, the light is absorbed and the laser beam quenched. The absorbed energy can then be released with a second light beam. According to ETH Zurich, the beam changes the molecule's quantum state, with the result that the light beam is amplified – the same principle as used by the laser. Vahid Sandoghdar, Professor at the Laboratory of Physical Chemistry of ETH Zurich, said: "Comparing the current state of this technology with that of electronics, we are somewhat closer to the vacuum tube amplifiers that were around in the 1950s than we are to today's integrated circuits." The effect has been created by cooling the molecule to 1K. At this temperature molecules appear to increase the surface area available for interaction with light and the enlarged surface area was approximately the diameter of the focused laser beam. Prof Sandoghdar added: "Many years of research will be needed before photons replace electrons in transistors. In the meantime, scientists will learn to manipulate and control quantum systems in a targeted way, moving them closer to the dream of a quantum computer."