A UNSW-led team of researchers has achieved a breakthrough that brings the prospect of a network of ultra-powerful quantum computers, connected via a quantum internet, closer to reality.
The team is the first in the world to have detected the spin, or quantum state, of a single atom using a combined optical and electrical approach.
The study is a collaboration between researchers from the ARC Centre of Excellence for Quantum Computation and Communication Technology based at UNSW, the Australian National University and the University of Melbourne. It is published in the journal Nature.
UNSW’s Professor Sven Rogge said the technical feat was achieved with a single atom of erbium – a rare earth element commonly used in communications - embedded in silicon.
“We have the best of both worlds with our combination of an electrical and optical system. This is a revolutionary new technique, and people had doubts it was possible. It is the first step towards a global quantum internet,” Professor Rogge said.
Quantum computers promise to deliver an exponential increase in processing power over conventional computers by using a single electron or nucleus of an atom as the basic processing unit - a quantum bit, or qubit.
Professor Rogge said researchers had previously used either an electrical or an optical method to read the spin of a single atom - where the information would be stored - but not both methods together.
Lead author of the study, UNSW’s Dr Chunming Yin, said the new approach opens up the possibility of using light to couple the atoms, or qubits, together to form a quantum computer.
“Using light to transfer information in the quantum state is easier than doing it electrically. Ultimately this will lead to quantum communications over long distances,” Dr Yin said.
Associate Professor Matthew Sellars, of the Australian National University, said it was a step towards connecting a solid state quantum computer to what will be the quantum internet.
“The quantum internet will allow separate quantum computers to be integrated and it will enable encrypted communications.”
Quantum communication systems will become critical for providing secure communications for government, military, defence, finance business and health industries.
To make the new quantum device, Associate Professor Jeffrey McCallum at the University of Melbourne used an ion implanter to shoot erbium atoms into a standard industrial silicon transistor.
When the atom was in a particular quantum state and laser light was shone on it, an electron was knocked off the atom. This was detected electrically, by the silicon transistor switching on.
Professor Rogge said the breakthrough was made possible by combining the expertise of the three groups. The next step would be to control the spin of the erbium atom, which should be relatively straightforward, and also to replicate their results using a phosphorus atom embedded in silicon.
The researchers said it will be at least another decade before the potential of quantum computation is fully realised.
Video (in English and Mandarin), Photos, and Backgrounder available
Professor Sven Rogge: firstname.lastname@example.org, +612 9385 5979, +61 (0) 466 748 373
(Sven also speaks Dutch and German)
Dr Chunming Yin: email@example.com, +612 9385 5591, +61 (0) 452 112 832
(Chunming also speaks Mandarin)
Associate Professor Jeffrey McCallum: +61 (0) 430 964 111, Associate Professor Matthew Sellars +61 (0) 437 620 280.
UNSW Science media: Deborah Smith, +612 9385 7307, +61 (0) 478 492 060, Deborah.Smith@unsw.edu.au
UNSW QUANTUM BACKGROUNDER
What is a quantum computer?
The quantum computers under development will be ultra-powerful devices that use the strange quantum properties of atoms or photons of light to solve complex problems and carry out certain calculations billions of times faster than today’s computers.
In a classical computer, information is stored in bits, which can be in two states – 0 or 1 - equivalent to a transistor device being switched on or off.
In a quantum computer, information is stored in quantum bits, or qubits - for example, in the spin, or magnetic orientation, of an individual electron bound to an atom, or the spin of a nucleus of an atom.
The electron spin can be up (1) or down (0), just as in a classical computer. But it can also be in a combination of both states at the same time, due to a quantum effect known as superposition.
This, together with entanglement of the quantum bits, allows exponentially larger amounts of information to be stored and processed in parallel using qubits.
A quantum computer with 300 qubits, for example, would be able to store as many different numbers as there are atoms in the universe.
To create a working qubit, scientists must complete a two-stage process: to control the spin state – the “write” function – and then detect this new spin state - the “read” function. They must also be able to couple the qubits together and transport them to form a quantum computer.
What will quantum computers be used for?
Important applications will include tasks where calculations need to be carried out in parallel on lots of data, such as economic modelling, fast database searches and modelling of quantum materials and biological molecules and drugs.
They will also be able to crack modern forms of encryption, requiring the development of alternative, ultra-secure quantum methods for transferring information.
This means quantum computers will be of enormous benefit for finance and healthcare industries, governments and security defence organisations.
The ARC Centre of Excellence for Quantum Computation and Communication Technology
The centre, which involves six universities and is led by Professor Michelle Simmons at UNSW, is a global leader in quantum computation and quantum communication.
The centre’s quantum computer research at UNSW has focused on making qubits out of single atoms embedded in silicon – the material that forms the basis of today’s computer chips.
Silicon has several advantages including that it is a cost-effective material to use, its properties are well understood, and it is already widely used in commercial electronics.
Recent quantum advances at UNSW
September 2010: Detection, or “reading”, of the spin state of a single electron in a single phosphorus atom implanted in silicon. (Professor Andrew Dzurak and Dr Andrea Morello)
January 2012: The narrowest conducting wires ever made in silicon were produced – just four atoms of phosphorus wide and one atom tall, with the same electrical current-carrying capacity as copper. (Professor Michelle Simmons)
February 2012: The world’s first working transistor consisting of a single atom was created, by precisely placing a phosphorus atom into a silicon crystal with unprecedented accuracy. (Professor Michelle Simmons).
September 2012: The world’s first working qubit based on a single atom in silicon was created, with researchers able both to write and read information using the spin of an electron bound to a phosphorus atom embedded in a silicon chip. They used microwaves to control the electron’s spin and read it out electronically. (Professor Andrew Dzurak and Dr Andrea Morello)
April 2013: The first qubit based on the nucleus of a single atom in silicon, with researchers able to control the nuclear spin of a phosphorus atom with microwaves and then read that value out with unprecedented accuracy electrically. (Professor Andrew Dzurak and Dr Andrea Morello)
May 2013: The spin of a single atom is read for the first time using a combined optical and electrical technique. This achievement, with an erbium atom in silicon, brings the prospect of a network of powerful quantum computers - connected via a quantum internet - closer to reality. (Professor Sven Rogge and Dr Chunming Yin)
What is quantum communication?
Quantum communication uses quantum principles to encrypt information onto photons of light so the information can be transmitted in an absolutely secure fashion. Any attempt to intercept the information can be immediately detected.
Quantum communication systems are limited to less than 200 kilometres at present, due to noise and losses during transmission.
If this can be improved they will become critical for national security and providing secure communications for government, military, defence, finance, business and health industries.
Why should Australia invest in this research?
The market impact of quantum computing and communication technology is estimated to be at least $US20 billion per year by 2020.
Australia has an international lead in optical and solid state quantum computation and in the field of quantum communication. By combining these technologies and accelerating efforts, Australia could be a leader of this industry in the 21st century.