On the right wavelength

A newly-discovered method to precisely control the movements of billions of individual electrons within a material could have applications in areas ranging from data encryption to the delivery of precise doses of radiation to cancer patients.

Scientists at the UK’s National Physical Laboratory (NPL) and Cambridge University’s Cavendish Laboratory have created a device that allows them to control the movement of these individual electrons by making them ride the crests of energy waves like surfers.

Using this method they can manipulate billions of individual electrons a second, which may allow them to develop new computing systems and increase the security of digital communication.



Semiconductor

‘The device is based on a piece of a semiconductor,’ said JT Janssen, head of science in NPL’s time and quantum team.

‘It is the same material used for high-mobility transistors — gallium arsenide. It is also used in satellite receivers.’

The device uses the electrons already present in a particular material, controlling their movement, using metallic contacts placed on top of the material.

As the material is pure, the electrons within it do not scatter a great deal. Instead, they are ballistic, moving like tiny bullets.

The metallic contacts are designed to either attract or repel electrons. If this is done in sequence then the electrons can be moved along in a particular direction, creating a current.

The movement is similar to a conveyor belt or Archimedes Screw. The wave can be moved from one side of the device to the other, with an external ammeter completing the circuit.

‘It is surprisingly simple,’ said Janssen. ‘The trick is picking up an electron a billion times a second.’

While small streams of electrons can already be produced, until now no one has found a way to deliver them in a controlled fashion at such a high rate. NPL’s method involves creating oscillating waves of electrostatic force that flow like surf rolling into a beach.

The applications for the control of so many individual electrons include better new computers and ensuring absolute security for digital communication.

All computer systems rely on a flow of electrical current through microprocessors. Currently, in normal PCs thousands of electrons flow in a disorderly manner in and out of each processor. This random motion causes significant amounts of heat to be produced. Great efforts are being made to cool processors but the problem still limits the computer’s efficiency.

By controlling individual electrons, exactly the right amount of current can be targeted at the processor at exactly the right time, allowing the computer to undertake more tasks, run more efficiently and cope with more requests at once.



New standard

The NPL researchers hope to create a new standard for electrical current, using a system that relies on the charge of a single electron rather than using measurements based on amperes.

The team has been working on the process for the past decade, and hope to have a workable standard within five to 10 years.

According to the laws of physics, the charge of an electron does not change wherever it is in the universe, meaning that using an electron-based standard, the charge within a device could be precisely defined.

This will allow instruments such as electrometers, which measure the electrical current in semiconductors, to be very precisely calibrated. It will also mean precise calibration of radioactive sources such as those used to deliver radiation to hospital patients, ensuring they receive the correct dose.

So far, the process has been made to work at a relatively high frequency of 3.5Ghz. However, Janssen said that the process has been losing a lot of electrons, meaning it must be modified to make it more accurate.

‘We are still at the proof of principle stage,’ he said. ‘Now we have to work on the accuracy and the reproducibility.’

Examination of how the process will behave at room temperature is also needed, as at present all work has been carried out at absolute zero.