The discovery of a previously unknown effect makes compact and ultra-fast control of rotating qubits possible.
Australian engineers have discovered a new way to precisely control individual electrons located in quantum dots that control logic gates. In addition, the new mechanism is less bulky and requires fewer parts, which may be necessary to create large-scale silicon quantum computers.
The accidental discovery, made by engineers from quantum computing startup Diraq and the University of New South Wales in Sydney, is detailed January 12 in the journal Nature Nanotechnology.
“This was a completely new effect that we had never seen before, and which we did not fully understand at first,” said lead author Dr. Will Gilbert, a quantum processor engineer at Diraq, a subsidiary of UNSW based in Sydney. facilities. “But it quickly became clear that this was a powerful new way to control spins in a quantum dot. And it was very exciting.”
Flip one qubit
An artist’s representation of a single qubit contained in a quantum dot flipping in response to a microwave signal. Credit: Tony Melov
Logic gates are the main component of all calculations; they allow “bits” or binary digits (0 and 1) to work together to process information. However, a quantum bit (or qubit) exists in both states at the same time, a state known as “superposition”. This allows for a variety of computational strategies, some exponentially faster, others running simultaneously, which is beyond the scope of classical computers. The qubits themselves are made up of “quantum dots,” tiny nanodevices capable of trapping one or more electrons. Accurate control of the electrons is necessary for the calculation.
Diraq engineers have discovered a new way to precisely control individual electrons located in quantum dots that control logic gates, bringing the reality of creating billion-qubit quantum chips closer to reality. In addition, the new mechanism is less bulky and requires fewer parts, which may be necessary to create large-scale silicon quantum computers. 1 credit
Use of electric fields instead of magnetic ones
While experimenting with different geometric combinations of devices as small as one billionth of a meter that control quantum dots, as well as different types of tiny magnets and antennas that power them, Dr. Tuomo Tanttu discovered a strange effect.
“I was trying to control the two-qubit gate very precisely, going through many different devices, slightly different geometries, different stacks of materials, and different control methods,” recalls Dr. Tantu, measurement engineer at Diraq. “Then this strange spike appeared. It seemed that the speed of rotation of one of the qubits increased, which I have never seen in the four years of these experiments.”
The engineers later realized that what they had discovered was a new way of manipulating the quantum state of a single qubit using electric fields instead of the magnetic fields they had previously used. Since the discovery was made in 2020, engineers have perfected the technique, which has become another tool in their arsenal to realize Dirac’s ambition to create billions of qubits on a single chip.
Acceleration of the qubit until it starts to rattle
An illustration of a single qubit as it starts accelerating in response to a microwave signal, and the electron starts spinning inside the quantum dot. Credit: Tony Melov
“This is a new way of manipulating qubits, and it’s less cumbersome to make: you don’t have to make cobalt micromagnets or an antenna right next to the qubits to create a control effect,” Gilbert said. “This eliminates the need to install additional structures around each door. So less mess.”
Controlling individual electrons without interfering with other nearby electrons is essential for processing quantum information in silicon. There are two established methods: “electron spin resonance” (ESR) using a built-in microwave antenna; and Electric Dipole Spin Resonance (EDSR) based on an induced gradient magnetic field. The newly discovered method is known as “internal spin-orbital EDSR”.
“We typically design our microwave antennas to create pure magnetic fields,” Dr. Tanttu said. “But this particular antenna design generated more electric field than we wanted, and it turned out to be a stroke of luck because we discovered a new effect that we can use to control