Another week, another interesting development in quantum computing. This time the task addressed is moving quantum information around inside a quantum computer. As usual, the qubit information is encoded in electron spin, so the goal is to move the electrons around without experiencing decoherence that would disrupt the information. Two teams published papers this week in Nature explaining how they’ve accomplished at least part of the task.
In both cases, the electrons are moved in a channel on a semiconductor surface, between two quantum dots, spaced 3 or 4 microns apart. The force to move the electrons is supplied by a small piezoelectric actuator. In one case it was possible to move an electron back and forth 60 times, for a total distance of .25 mm. Although the total travel time is less than the normal decoherence time, both teams have yet to prove that decoherence is avoided.
Two independent groups of physicists have taken an important step towards the creation of a practical quantum computer by showing how to transfer single electrons over relatively long distances between quantum dots. Both schemes involve using sound waves on the surface of a material to propel electrons between the quantum dots – which are sub-micron-sized pieces of semiconductor. The teams are confident that they will soon be able to show that electrons arrive at their destination with their quantum information intact, making the system a viable “quantum data bus” for a quantum computer.