Researchers have also created qubits from the “up” or “down” spin-states of electrons on quantum dots. But they lacked the ability to control these states well enough to perform calculations using them. A team at Delft University of Technology in the Netherlands has now created a device that can manipulate these states using conventional microchip fabrication technology.
Schematic diagram of the Loss & DiVincenzo computer.
AFM Image of a double quantum dot, integrated with quantum point contacts on both sides.
“This is a breakthrough experiment,” says Guido Burkard, a physicist at the University of Basel in Switzerland, who was not involved in the research. “The major benefit of making a qubit using this method is that they are built upon existing semiconductor technology.”
The Dutch team’s device was made using conventional microchip lithography. It consists of two electrodes that apply voltage across two semiconducting quantum dots – pieces of gallium arsenide each 100 nanometres across – to form a simple circuit.
The voltage causes electrons to hop between the dots. However, each dot can only accommodate one electron at a time and electrons with matching spin states cannot jump onto the same dot.
Burkard says electron-spin qubits could now rapidly catch up with more established methods of quantum computing. “I see no roadblocks to moving towards the first implementation of small quantum algorithms using electron-spin qubits,” he says.
Introduction to quantum algorithms