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Quantum simulators & super civilisations

Pete Wilton

A team, including Oxford University scientists, recently used a quantum computer to calculate the precise energy of molecular hydrogen.

The breakthrough [more here], reported in Nature Chemistry, is the first step towards using one quantum system (in this case entangled photons) to model another (such as a chemical reaction).

I asked Jacob Biamonte from Oxford University's Computing Laboratory, an author of the paper, about the work and what harnessing such 'quantum simulations' might mean for science and even the conquest of space...

OxSciBlog: Why is calculating the precise energy of hydrogen so hard?
Jacob Biamonte: The equations that predict unknown properties of matter have been around for almost 100 years, if only we had a computer capable of solving them! Molecular hydrogen represents an excellent test case for a prototype dedicated quantum processor: a quantum chemistry simulator.

A future quantum simulator will help us understand the nature of matter - particularly chemical reactions - by finally providing solutions to long standing problems, that we simply have been unable to solve using even the world’s largest classical computers.

OSB: How can quantum computing help?
JB: The thought process of humans has evolved to reason in the world we live in. Although these effects are crucial to life itself, quantum effects are essentially unnoticeable in our day-to-day lives. Like the conscious thought process of our brain, machines that operate using 'classical sequences' face grave difficultly modelling systems, such as molecules, that operate by 'quantum sequences'.

Quantum sequences are not only difficult for our classical brains to understand, but at least very difficult and likely even impossible to accurately model using any device that operates by classical sequences. Quantum simulators overcome this problem as they naturally operate using quantum sequences - it is just up to our classical brains to ask them the right questions, and many of the most important ones are about quantum chemistry.

OSB: What was the biggest obstacle you had to overcome?
JB: Let's consider a classical sequence as an ordering of say a dozen events on a time line. These events are ordered in an obvious (classical) manner: the twelfth event depends on the eleventh down the line to the first, and so on. To get any idea of how much of an obstacle quantum mechanics is for our classical brains to understand, let's consider the quantum version of the same sequence of a dozen events:as a quantum sequence, the  first event on the time line can be made to depend on the twelfth event, occurring in the future! This is not Star Trek!

A few generations of scientists thought it was a 'bug' in quantum theory - first pointed out by Erwin Schrödinger in a paper he wrote during his time in Oxford about 80 years ago. 60 years later it was Oxford Professor David Deutsch who decided to turn this 'bug' into a feature, and said we should use it as a new powerful computational resource.

OSB: What does your project tell us about how 'quantum systems can help model quantum systems'?
JB: A date in history that some of us should experience in our lifetimes will be the day a quantum computer out-performs the world’s fastest classical super computer. It is almost certain the problem solved will be an intractable chemical simulation, such as the currently unattainable task of finding the ground state of even a modest molecule, like caffeine.

This represents a step forward that is difficult to imagine. What if we did not know how to control electricity, but had blueprints for iPhones, electric motors, and dishwashers? Material Scientists and Quantum Chemists are in this situation! The impact a quantum simulator will have on this world is as difficult to imagine as an iPhone would have been in the Dark Ages.

OSB: How do you hope to take this research forward?
JB: This research is important for the human species! We need to know things about matter that it seems only quantum computers will be able to tell us. This will take our science forward, turn our world into a super civilisation almost overnight, lead to rapid and wild advances in medicine, and likely lead to materials needed to construct spacecraft.

We are gathering synergy in the quantum computing research community, and more interest on using these devices as a tool to explore physics and chemistry. We have plans to start a webpage with experimental benchmarks, providing chemistry benchmarks to the small quantum processors of today, and leading up to an exact resource count for the first classically impossible calculation that a quantum simulator will solve. It's exciting, it's the future, and it's being built now!

Jacob Biamonte is based at Oxford University's Computing Laboratory