Science & Technology, Australia (Commonwealth Union) – Qubits, or quantum bits, are the fundamental building blocks of quantum computers. Unlike classical bits, which can only be in two states (either 0 or 1), qubits can exist in a superposition of both states, meaning that they can represent multiple values simultaneously. Qubits play a key role in the development of quantum computing and have the potential to revolutionize many fields, making them a key area of research and innovation in the world of technology. Qubits also have applications in other areas, such as simulating quantum systems, where their ability to represent multiple states at once can be used to model complex quantum phenomena. In addition, they can be used to implement quantum error correction, which is essential for building reliable quantum computers.
A University of New South Wales (UNSW) study has revealed a new type of qubit in silicon, known as ‘flip-flop’ qubit, capable of making way for the creation of a large-scale quantum computer.
Professor Andrea Morello led his team that just showed the operation for the new flip-flop’ qubit, that brings together the exquisite quantum properties of single atoms, with simple controllability applying electric signals, like them applied in ordinary computer chips.
“Sometimes new qubits, or new modes of operations, are discovered by lucky accident. But this one was completely by design,” said Professor Morello. “Our group has had excellent qubits for a decade, but we wanted something that could be controlled electrically, for maximum ease of operation. So we had to invent something completely new.”
The group of Professor Morello was the 1st from across the globe to show that applying the spin of an electron together with the nuclear spin of a single phosphorus atom in silicon can be utilized as ‘qubits. He indicates that while both qubits do extraordinarily good on their own, they need oscillating magnetic fields for operation.
“Magnetic fields are difficult to localise at the nanometre scale, which is the typical size of the individual quantum computer components. This is why the very first proposal for a silicon quantum bit envisaged having all the qubits immersed in a uniform oscillating magnetic field, applied across the whole chip, and then using local electric fields to select which qubit gets operated.”
Professor Morello’s team made the realization, a few years back that by the definition of the qubit as the combined up-down / down-up orientation of the electron and the nucleus of the atom can allow controlling such qubit utilizing just the electric fields. The result obtained is the experimental revelation of that visionary concept.
The electrical control of the ‘flip-flop’ qubit by displacing the electron from the nucleus is joined by a significant side effect. The negative charge is displaced further from a positive charge, where an electric dipole is produced. The placement of 2 or more electric dipoles in the proximity of each other paves the way for strong electrical coupling between them, capable of mediating multi-qubit quantum logic operations of the kind needed for carrying out helpful quantum computations according to researchers.
Professor Morello indicated that the standard method for coupling spin qubits in silicon is the placement of electrons near each other that they effectively ‘touch.
He further indicated that it needs the qubits to be put on a grid of a few 10s of nanometres in pitch. The engineering challenges conducting it are quite serious. When compared, electric dipoles are not required to ‘touch’ each other, as they impact each other from the distance. Their theory shows that 200 nanometres is the ideal distance for fast and high-fidelity quantum operations.
“This could be a game-changing development, because 200 nanometres is far enough to allow inserting various control and readout devices in between the qubits, making the processor easier to wire up and operate.”
As the focus on quantum computers increases in research institutions and corporations across the world as they seek the technology to solve a variety of different problems, this new finding is likely to be a significant development.
