An international team of researchers led by the University of Bristol have demonstrated that light can be used to implement a programmable, multi-functional quantum processor.

The team has developed a silicon chip that can be used as a scientific tool to perform a wide array of quantum information experiments, while at the same time showing the way to how fully functional quantum computers might be developed from mainstream chip-making processes.

Quantum computers are instead based on “qubits” that can be in a superposition of the 0 and 1 states. Multiple qubits can also be linked in a special way called quantum entanglement. These two quantum physical properties provide the power to quantum computers.

One challenge is to make quantum computer processors that can be re-programmed to perform different tasks in a similar way to today’s computers

The chip developed by the Bristol team can fully control two qubits of information within a single integrated chip. This means any task that can be achieved with two qubits, can be programmed and realised with the device.

“What we’ve demonstrated is a programmable machine that can do lots of different tasks,” said Dr Xiaogang Qiang, who now works in the National University of Defence Technology in China. “It’s a very primitive processor, because it only works on two qubits, which means there is still a long way before we can do useful computations with this technology. But what is exciting is that it the different properties of silicon photonics that can be used for making a quantum computer have been combined together in one device. This is just too complicated to physically implement with light using previous approaches.”

“We need to be looking at how to make quantum computers out of technology that is scalable, which includes technology that we know can be built incredibly precisely on a tremendous scale,” said Dr Jonathan Matthews, a member of the research team based at the Quantum Engineering Technology (QET) Labs at the University of Bristol. “We think silicon is a promising material to do this, partly because of all the investment that has already gone into developing silicon for the micro-electronics and photonics industries. And the types of devices developed in Bristol are showing just how well quantum devices can be engineered.

“A consequence of the growing sophistication and functionality of these devices is that they are becoming a research tool in their own right — we’ve used this device to implement several different quantum information experiments using nearly 100,000 different re-programmed settings,” he said.

Quantum Engineering Technology Labs – University of Bristol