UNSW researchers entangled atomic nuclei via electrons, achieving quantum communication at scales compatible with current computer chips, advancing silicon quantum computing.
UNSW engineers developed quantum entangled states using the spins of two atomic nuclei. Entanglement is crucial for quantum computing’s advantages over conventional systems. This research, published in Science on September 18, represents a step toward large-scale quantum computers.
Lead author Dr. Holly Stemp stated this achievement enables the construction of future quantum computing microchips using existing technology and manufacturing processes. She noted, “We succeeded in making the cleanest, most isolated quantum objects talk to each other, at the scale at which standard silicon electronic devices are currently fabricated.”
Quantum computer engineering balances shielding computing elements from interference with enabling their interaction for computations. This challenge contributes to the diversity of quantum hardware approaches. Some offer speed but suffer from noise, while others are shielded but difficult to operate and scale.
The UNSW team utilized the nuclear spin of phosphorus atoms, implanted in a silicon chip, to encode quantum information. Scientia Professor Andrea Morello from UNSW’s School of Electrical Engineering & Telecommunications described the atomic nucleus spin as “the cleanest, most isolated quantum object one can find in the solid state.”
Professor Morello detailed the group’s prior work over 15 years, which involved breakthroughs in this technology. They demonstrated holding quantum information for over 30 seconds and performing quantum logic operations with less than 1% errors. He stated they were “the first in the world to achieve this in a silicon device.” However, he noted the isolation benefiting atomic nuclei made connecting them in a large-scale quantum processor difficult.
Previously, operating multiple atomic nuclei required them to be very close within a solid, surrounded by a single electron. Dr. Stemp explained that while an electron can “spread out” to interact with multiple atomic nuclei, its range is limited. She added, “adding more nuclei to the same electron makes it very challenging to control each nucleus individually.”
The breakthrough involved atomic nuclei communicating through electronic ‘telephones,’ which are electrons. Dr. Stemp used the metaphor of people in a sound-proof room, where conversations were clear but limited in scale. The ‘telephones’ enable communication between rooms, creating more scalable interactions while maintaining isolation.
Mark van Blankenstein, another author, explained that two electrons can “touch” at a distance due to their ability to spread out. If each electron couples to an atomic nucleus, the nuclei can communicate through them. The distance between the nuclei in the experiments was approximately 20 nanometers. Dr. Stemp highlighted that if a nucleus were scaled to human size, this distance would be comparable to that between Sydney and Boston.
She emphasized that 20 nanometers is the scale of modern silicon computer chips used in personal computers and mobile phones. This means manufacturing processes developed by the semiconductor industry can be adapted for quantum computers based on atomic nuclei spins.
These devices are compatible with current computer chip manufacturing. Phosphorus atoms were introduced into the chip by Professor David Jamieson’s team at the University of Melbourne, using ultra-pure silicon from Professor Kohei Itoh at Keio University in Japan.
By eliminating the need for atomic nuclei to be attached to the same electron, the UNSW team addressed a key obstacle to scaling silicon quantum computers based on atomic nuclei. Professor Morello described their method as “remarkably robust and scalable.” He added that in the future, more electrons could be used and shaped to spread nuclei further. “Electrons are easy to move around and to ‘massage’ into shape, which means the interactions can be switched on and off quickly and precisely. That’s exactly what is needed for a scalable quantum computer.”
