Researchers discovered a technique to control millions of spin qubits that are needed for extraordinarily complex calculations.
Spin qubits are the basic units of information in a silicon quantum processor. In these units, information is stored in the spin momentum of an electron. A spin of a single electron in a magnetic field can either be in the spin down (low energy) or in the spin up (high energy) state. The only thing throttling back the implementation of quantum computers is a way to control these qubits.
Researchers from University of New South Wales, Sydney, have discovered a new technique they say will be capable of controlling millions of spin qubits that are needed for extraordinarily complex calculations, without taking up valuable space with more wiring, using more electricity, and generating more heat.
Dr. Jarryd Pla, a faculty member in UNSW’s School of Electrical Engineering and Telecommunications says, “Up until this point, controlling electron spin qubits relied on us delivering microwave magnetic fields by putting a current through a wire right beside the qubit.”
But this poses a challenge if we want to scale up to a higher number of qubits that a quantum computer will need.
“First off, the magnetic fields drop off really quickly with distance, so we can only control those qubits closest to the wire. That means we would need to add more and more wires as we brought in more and more qubits, which would take up a lot of real estate on the chip.”
“First we removed the wire next to the qubits and then came up with a novel way to deliver microwave-frequency magnetic control fields across the entire system. So in principle, we could deliver control fields to up to four million qubits,” says Dr. Pla.
The researchers introduced a new component called dielectric resonator. When microwaves are directed towards the resonator, it focuses the wavelength of the microwaves down to a much smaller size.
“There are two key innovations here. 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.”