3D confined electron wave functions in a quantum dot

Hybrid connected system a step forward for quantum computing

Researchers have connected two different quantum systems, making them cooperate in order to make up for each other’s flaws.

Describing their experiment in the latest issue of the Physical Review Letters, scientists from the Universities of Bonn and Cambridge demonstrated how to connect quantum dots with charged atoms, or ions, marking an important step towards the development of a quantum computer.

While quantum dots are able to process and disseminate information extremely quickly, they are unable to retain the results of the calculations for any usable period of time.

Ions, on the other hand, while not suited for speedy calculations can store information for many minutes.

By connecting the two systems, the researchers have virtually managed to make each system mitigate the other's shortcomings.

"We used the photon to excite an ion", explained Professor Michael Köhl from the Institute of Physics at the University of Bonn. "Then we stored the direction of polarisation of the photon."

The photons are produced when electrons are stored in the quantum dots, reflecting the quantum state of the quantum dot by vibrating in a specific plane.

To make use of those extremely short-lived light impulses, the researchers connected the quantum dots via optic fibres to the ions. The fibres transported the information encoded in the light to the ions. The researchers enhanced the process by trapping the ions between two mirrors, virtually making the photon bounce back and forth until it was absorbed by the ion.

"By shooting it with a laser beam, we were able to read out the ion that was excited in this way," Professor Köhl said. "In the process, we were able to measure the direction of polarisation of the previously absorbed photon."

The experiment proved that the state of the quantum dot can be preserved in the ion for several minutes.

Many researchers around the world are currently studying quantum dots - essentially miniature electron storage units - and pinning their hopes on them for future super-fast quantum computers.

Quantum dots can be produced using the same techniques as normal computer chips, once structures on those chips have been miniaturised to the extent that they hold just one single electron. Conventional chips used in current PCs carry between 10 to 100 electrons.

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