Scientists at UNSW have achieved a breakthrough in quantum computing by entangling nuclear spins across distances of up to 20 nanometers in a silicon chip - the same scale as modern computer transistors^[1].

The team demonstrated a two-qubit controlled-Z logic operation between the nuclear spins of two phosphorus atoms, with each atom binding separate electrons that mediate the interaction through exchange coupling^[1:1]. They proved genuine quantum entanglement by preparing and measuring Bell states with 76% fidelity^[1:2].

“The spin of an atomic nucleus is the cleanest, most isolated quantum object one can find in the solid state,” said Professor Andrea Morello from UNSW^[2]. Previous methods required nuclei to be very close together and share a common electron, limiting scalability. This new approach uses separate electrons as “telephones” to let distant nuclei communicate^[2:1].

Lead author Dr. Holly Stemp explains the significance: “You have billions of silicon transistors in your pocket or in your bag right now, each one about 20 nanometers in size. This is our real technological breakthrough: getting our cleanest and most isolated quantum objects talking to each other at the same scale as existing electronic devices.”^[2:2]

The method remains compatible with current semiconductor manufacturing, using phosphorus atoms implanted in ultra-pure silicon. Professor Morello notes: “Our method is remarkably robust and scalable. Here we just used two electrons, but in the future we can even add more electrons, and force them in an elongated shape, to spread out the nuclei even further.”^[2:3]