As revolutionary as they could be, quantum computers still have a few kinks to iron out, such as controlling more than a few dozen qubits at once. Now, researchers at the University of New South Wales (UNSW) have found a way to control potentially millions of qubits at once, by adding a crystal prism to the chip.
In silicon quantum processors, information is encoded into the “spin” of an electron, with up and down spins representing ones and zeroes. This is adjusted through a magnetic field, which is usually produced through wires running alongside the qubits. That works for a few dozen qubits, as has been demonstrated in proof-of-concept chips so far, but to get to the really powerful stuff we’ll need hundreds of thousands or even millions of qubits. All those wires will take up valuable space in the chip, and generate too much heat.
So for the new study, the UNSW team developed a new way to deliver a magnetic field to a huge number of qubits at once. The key is a crystal prism called a dielectric resonator, which sits directly above the silicon chip. Microwaves are directed into this prism, focusing the wavelength down even smaller, below one millimeter, which creates a magnetic field that controls the spins of the qubits below.
“There are two key innovations here,” says Jarryd Pla, corresponding author of the study. “The first is that we don’t have to put in a lot of power to get a strong driving field for the qubits, which crucially means we don’t generate much heat. The second is that the field is very uniform across the chip, so that millions of qubits all experience the same level of control.”
In the current experiments, the researchers were able to use this field to flip the states of the individual qubits. More work will still need to be done to produce the superposition of both states at once, but the team says that this method should eventually allow control of up to four million qubits at once.
Crystal prism provides better control to quantum computer chips [New Atlas]