Photo: Pixabay
Photo: Pixabay

OPINION: This is a crystallising time in quantum computers

By Louis Fourie Time of article published Mar 8, 2019

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CAPE TOWN – After many years of dreaming about building quantum computers, scientists have eventually succeeded in developing machines that are able to handle complex mathematical models, hugely increasing the range and accuracy of weather forecasts and financial market predictions, among other things.

Worldwide, researchers are racing to add more qubits (a qubit or quantum bit is the basic unit of quantum information) to powerful processors in their endeavour to build the most powerful computer.

In quantum computing, the power grows exponentially with the number of qubits.

According to John Preskill, a theoretical physicist at the California Institute of Technology, quantum computers reach the equivalent of about 10 quadrillion bits (on classical computers) somewhere around 49 or 50 qubits and become capable of calculations no classical computer would be able to match.

Google has already crafted a 72-qubit processor, followed by IBM with a 50-qubit processor, and Intel with a 49-qubit processor.

D-Wave boasts with a commercial quantum computer of 2000 qubits. However, these qubits implement quantum annealing instead of a universal model of quantum computation.

Quantum annealing is great for optimising solutions to problems by quickly searching over space and finding a solution.

In building quantum computers scientists and industry players have focused on a few approaches.

The first approach, followed by Google, IBM, Intel, Rigetti and D-Wave, is to use superconductors.

The electronic circuits are cooled to cryogenic temperatures near -273.15 degrees Celsius, or absolute zero - several hundred times lower than the temperature of interstellar space.

At this temperature the metal niobium begins to display distinct quantum mechanical properties, turning them into superconductors where electric current flows with nearly no resistance.

The second approach relies on trapped ions or charged atoms.

The oscillating charges (in both the wires and the trapped ions) function as qubits, which can be utilised to carry out the computer’s processes.

One of the groundbreaking solutions in this approach is the possible use of time crystals that would outperform superconductor systems according to scientists at Aalto University in Finland.

MIT theoretical physicist and Nobel laureate, Frank Wilczek, originally proposed the concept of time crystals in 2012.

He posited that if the properties of matter change over time rather than in space that it might create new states of matter.

Five years later, two teams of researchers created time crystals that bend the laws of space and time.

The team from the University of Maryland used a chain of charged particles from the scarce earth element ytterbium and held it in place in a vacuum chamber by a magnetic field created by a laser beam while flipping the spin of the electrons by another laser to keep the ions out of equilibrium.

Meanwhile, the other team from Harvard University created an artificial lattice using small imperfections in synthetic diamonds.

Although radically different structures, both teams demonstrated the quantum system behind their endeavours, and both produced new materials that work as time crystals.

But what exactly is a time crystal?

Time crystals are systems of atoms that organise themselves in time the way solids crystallise in space and represent a new phase of matter independent from the well-known solids, liquids and gases that comprise our known universe.

Newtonian laws of physics revolve around symmetries. Before a liquid crystallises, the space it occupies is symmetric.

For example, if you sample the bottom, the top, or the middle of a cup of water, it would be the same, thus occupying a symmetric space. But when the water crystallises, the atoms form rigid, set patterns.

The space occupied by the crystal has become periodic. The crystal has broken spatial symmetry because of the repeating patterns in some directions rather than being the same in all directions.

Just as ordinary crystals are characterised by their repeating patterns in space, time crystals - which are always moving - have the unique feature that their motion exhibits repeating patterns in time or periodicity.

As the periodicity of crystals breaks the symmetry of space, so does the periodicity of time crystals break the symmetry of time. Their atoms spin continually, changing directions as some pulsating force flips them.

Quite literally, time crystals “tick” like a clock and their atoms flip at a constant, periodic frequency.

But this is not the reason why they are called time crystals - the name comes from the fact that the crystals’ atomic structure repeats in time, which is why they seem to oscillate at set frequencies.

Time crystals never find equilibrium the way that a diamond does, so they are now considered one of the few examples of non-equilibrium matter known to scientists.

This is of importance in building a quantum computer, which is basically a quantum system far away from equilibrium.

As quantum computers become more powerful, perhaps through the successful crystallising of time, they will in future transform computing and business paradigms by solving computational problems that are currently intractable for today’s classical computers.

Professor Louis Fourie is the deputy vice-chancellor: Knowledge & Information Technology - Cape Peninsula University of Technology.


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