UW-Madison team to lay new foundation

A team of researchers at the University of Wisconsin-Madison plan to use silicon germanium quantum dots to build the foundation for a new generation of super computers.

A team of engineering and physics researchers at the University of Wisconsin-Madison plan to use silicon germanium quantum dots to build the foundation for a new generation of super computers.

The US Army Research Office chose to fund the UW-Madison researchers with a three-year, $1.2 million grant to develop a semiconductor-based quantum gate or qubit.

At the centre of the invisible atomic world of quantum computing is the quantum dot, a nanometer-scale ‘box’ that holds a distinct number of electrons. The number can be manipulated by changing electrical fields near the dot.

A quantum computer would use these dots to take advantage of superposition, a quantum phenomenon in which an electron would have its spin state both up and down at the same time. Where a classical computer uses an on or off state to represent bits of information in binary code, a quantum computer uses the superposition as qubits.

With superposition, a qubit is in neither the zero nor the one state before being measured, but exists as both zero and one simultaneously. The spin state of the particle is determined at the time it is measured.

The team will combine advanced physics theory, silicon-germanium heterostructured materials, low-temperature and high frequency measurements to build an elemental piece of a quantum computer, called a solid-state Controlled-NOT logic gate.

A useful quantum computer will require a chain of thousands of qubits. Other approaches have formed qubits using nuclear magnetic resonance or by trapping individual atoms in a vacuum but have been limited by the inability to link together large numbers of qubits.

The UW-Madison team’s process is said to use new science and existing technology similar to complementary metal-oxide semiconductor (CMOS) technology. That means if one qubit can be made, the process likely could be scaled to make and link qubits by the thousands.

The researchers predict their success could result in the first useful quantum computer in 10 to 30 years. The team has already disclosed its approach to the Wisconsin Alumni Research Foundation for consideration of a patent.

‘That is what is so exciting,’ said Professor Mark Eriksson. ‘Here we are building a new type of quantum dot that hasn’t been made before, and if we can do this successfully, the infrastructure is out there so that the technical community should be able to run with this.’