ARDR STORY

Entangling investment

The University of New South Wales has opened new quantum computing laboratories that will support the work the ARC Centre of Excellence for Quantum Computation and Communication Technology (CQC2T).

The new laboratories will house six new scanning tunnelling microscopes that can be used to manipulate individual atoms, as well as six cryogenic dilution refrigerators that can reach ultra-low temperatures close to absolute zero.

False-colour electron microscope image of a nanoelectronic device produced by Michelle Simmons' lab revealing a phosphorus atom placed within a silicon matrix. The insert illustrates the qubit concept: while the classical bit is either in the "0" or "1" state, a qubit can be any combination or superposition of these at the same time. Credit: Electron microscope image from UNSW; insert modified from Misha Brodsky

According to the university, the new facility will double the productive capacity of the CQC2T, which aims to develop a prototype of a silicon-based quantum computer.

Late last year, CQC2T's director Professor Michelle Simmons won major funding support for the project, including contributions from the Australian Government ($26 million), Telstra $10 million) and the Commonwealth Bank ($10 million).

The approach of Professor Simmons' research team at UNSW differs from many other developments in quantum computing as it focusses on a silicon-based physical architecture.

Recently, the centre's researchers and collaborators reported major advances by demonstrating that they could precisely place single atoms of phosphorous atoms into the silicon matrix, and detect and manipulate the quantum state of their electrons, including for - at this stage - simple calculations.

The success of the group placed it at the forefront of quantum computing research, and marked a revival of silicon as a promising material for a quantum computing device.

According to Professor Simmons, a ten-qubit prototype quantum integrated circuit could now be built within five years, and then lead to the first commercially available quantum computing devices within another 5-10 years.

Recent UNSW-led research milestones include:

In 2012, a team led by Professor Simmons created the world’s first single-atom transistor by placing a single phosphorus atom into a silicon crystal with atomic precision. Her team also produced the narrowest conducting wires ever made in silicon, just four atoms of phosphorus wide and one atom high.
In 2012, researchers led by UNSW Professor Andrea Morello created the world’s first qubit based on the spin of a single electron on a single phosphorus atom embedded in silicon. In 2014, his group then went on demonstrate that these qubits could be engineered to have the longest coherence times (greater than 30 seconds) and highest fidelities (>99.99%) in the solid state.
In 2013, UNSW Scientia Professor Sven Rogge demonstrated the ability to optically address a single atom, a method that could allow the long-distance coupling of qubits.
In 2015, researchers led by UNSW Scientia Professor Andrew Dzurak built the first quantum logic gate in silicon – a device that makes calculations between two qubits of information possible. This clears one of the critical hurdles to making silicon-based quantum computers a reality.

Coinciding with the opening of the laboratories, the UNSW researchers reported in Nature Communications a successful proof-of-principle experiment showing that a small group of individual atoms placed very precisely in silicon can act as a quantum simulator. The researchers placed 'dopant' atoms of boron only a few nanometres from each other in a silicon crystal. The electrons of these atoms behaved like valence bonds, the 'glue' that holds matter together when atoms with unpaired electrons in their outer orbitals overlap and bond.

The team was able to directly measure the electron 'clouds' around the atoms and the energy of the interactions of the spin, or tiny magnetic orientation, of these electrons. They were also able to correlate the interference patterns from the electrons, due to their wave-like nature, with their entanglement, or mutual dependence on each other for their properties.

The researchers say that the electrons behaved in accordance with the Hubbard model, which describes the unusual interactions of electrons due to their wave-like properties and spins.

The team also made a find that is counterintuitive yet typical for quantum systems: the entanglement of the electrons in the silicon chip increased the further they were apart.

More information: www.unsw.edu.au