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Making memories - practical quantum computing is one step closer



20 June 2013

Quantum computing may one day revolutionise information processing, by providing a means to solve problems so complex that no classical computer could ever hope to solve them, with applications in codebreaking, materials science, and physics. But figuring out how to engineer such a machine, including vital subsystems like quantum memory, remains elusive.

A team from the University of Sydney and Dartmouth College in the US, have realised a major breakthrough, developing a new approach to preserving quantum states for exceptionally long times in a quantum memory, with details published in Nature Communications on 19 June 2013.

Dr Michael Biercuk, Director of the Quantum Control Laboratory in the University of Sydney's School of Physics and ARC Centre for Engineered Quantum Systems, led a team who have developed a new approach to preserve quantum states for exceptionally long times in a quantum memory.
Dr Michael Biercuk, Director of the Quantum Control Laboratory in the University of Sydney's School of Physics and ARC Centre for Engineered Quantum Systems, led a team who have developed a new approach to preserve quantum states for exceptionally long times in a quantum memory.

"We've developed an entirely new way of designing a practically useful quantum memory, which is a key need for future quantum computers," said Dr Michael J. Biercuk, Director of the Quantum Control Laboratory in the University of Sydney's School of Physics and ARC Centre for Engineered Quantum Systems.

The team led by Dr Biercuk includes University of Sydney Honours student Jarrah Sastrawan, research fellow Dr David Hayes, and PhD student Todd Green, with the work carried out in collaboration with colleagues from Dartmouth College, Dr Kaveh Khodjasteh and Professor Lorenza Viola.

In the worldwide drive to build a useful quantum computer, the simple-sounding task of effectively preserving quantum information in a quantum memory is a major challenge.

"One of the biggest challenges in quantum systems is error susceptibility. The very same physics that makes quantum computers potentially powerful also makes them likely to experience errors, even when quantum information is just being stored idly in memory. Keeping quantum information 'alive' for long times while remaining accessible to the computer is a key problem in the field," explained Dr Biercuk.

The research community, including Dr Biercuk's team, has spent considerable effort on figuring out how to prevent errors, translating techniques from control theory into the quantum regime.

With these new results the team has demonstrated a path to what is considered a holy grail in the community: storing quantum states with high fidelity for exceptionally long times - even hours according to their calculations. Today, most quantum states survive for tiny fractions of a second.

"Our new approach addresses key issues in engineering a useful quantum memory. It allows us to simultaneously achieve very low error rates and very long storage times. But our work also addresses a vital practical issue - providing small access latencies, enabling on-demand retrieval with only a short time lag to extract stored information."

The team's new method is based on special techniques to build in error resilience at the level of the quantum memory hardware. These are the basic protocols that last year earned Dr Biercuk a place as a finalist for the Eureka Prize for Innovations in Computer Science.

"We've now developed the quantum 'firmware' appropriate to control a practically useful quantum memory. But vitally, we've shown that with our approach a user may guarantee that error never grows beyond a certain level even after very long times, so long as certain constraints are met. The conditions we establish for the memory to function as advertised then inform system engineers how they can construct an efficient and effective quantum memory. Our method even incorporates a wide variety of realistic experimental imperfections," said Dr Biercuk.

The new results continue the team's success in bringing quantum computers closer to practical reality. Last year Dr Biercuk and colleagues demonstrated a special-purpose quantum simulator with computational potential so extraordinary it would take a standard supercomputer larger than the known universe to match it.

Read the paper in Nature Communications at: www.nature.com/ncomms/2013/130619/ncomms3045/abs/ncomms3045.html


Contact: Katynna Gill

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