Technique holds promise for large scale quantum computing
1 min read
In what has been described as a key step towards creating a working quantum computer, Princeton researchers have developed a method that allows the quick and reliable transfer of quantum information throughout a computing device.
The finding, by a team led by Jason Petta, could eventually allow engineers to build quantum computers consisting of millions of quantum bits, or qubits. So far, quantum researchers have only been able to manipulate small numbers of qubits, not enough for a practical machine.
"The whole game at this point in quantum computing is trying to build a larger system," said Andrew Houck, an assistant professor of electrical engineering who is part of the research team.
To make the transfer, Petta's team used a stream of microwave photons to analyse a pair of electrons trapped in a tiny cage called a quantum dot. The spin state of the electrons serves as the qubit, a basic unit of information. The microwave stream allows the scientists to read that information.
"We create a cavity with mirrors on both ends – but they don't reflect visible light, they reflect microwave radiation," Petta explained. "Then we send microwaves in one end, and we look at the microwaves as they come out the other end. The microwaves are affected by the spin states of the electrons in the cavity, and we can read that change."
Over the years, scientists have developed techniques to observe spin states without disturbing them. But analysing small numbers of spins is not enough; millions will be required to make a real quantum processor.
To approach this problem, Petta's team combined techniques from two branches of science. From materials science they used a structure called a quantum dot to hold and analyse electrons' spins; and from optics, they adopted a microwave channel to transfer the spin information from the dot.
To make the quantum dots, the team isolated a pair of electrons on a small section of material called a semiconductor nanowire. They then created small cages along the wire. The cages were set up so that the electrons could settle into a particular cage depending on their energy level.
"The methods we are using here are scalable, and we would like to use them in a larger system," said Petta. "But to make use of the scaling, it needs to work a little better. The first step is to make better mirrors for the microwave cavity."
