Today in non-depressing news: Boffins build biggest quantum sims

Each packed with 50-plus qubits, it's a stepping stone to next-gen computing. Possibly

Strings of atomic qubits are used to probe quantum magnetism. Image credit: J. Zhang et al.; graphic: E. Edwards

Two teams of researchers have created the world's largest publicly known quantum simulators – a type of quantum computer – each containing more than 50 qubits to model complex interactions between matter that cannot be performed with a conventional supercomputer.

Quantum simulators are a restricted type of quantum computer made up of qubits – the quantum analogue of a bit used in traditional computing, where the states 0 and 1 can be in a superposition of both states at the same time. They aren’t a general-purpose quantum computer, and can only simulate specific situations, such as quantum magnets. So no, they can't play Crysis.

A group of physicists at the University of Maryland and the National Institute of Standards and Technology in America did this by trapping 53 ytterbium ions using gold-coated electrodes. The second team from Harvard University and Massachusetts Institute of Technology, again America, controlled 51 rubidium atoms with laser beams. The results from both independent studies were published in Nature on Thursday.

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The ytterbium ions act basically like magnets: they all have the same charge and repel one another. As they push each other away, an electric field generated by electrodes forces them back together. The repulsive and attractive forces balance each other out and the ions interact with each other to align uniformly like the poles of a magnet.

It’s a similar situation with the rubidium atoms, but since they do not have an electric charge they are first forced into the same state by a laser. Next, a second laser pulse makes them to act like magnets where all the qubits can point in the same direction to act like a ferromagnet or scatter in different directions giving no overall magnetisation.

The researchers manipulated both quantum simulators by changing the strengths of the laser beams and electric field to see what order persists under different conditions. This allowed them to observe how the qubit magnets organize themselves over the different states.

Alexey Gorshkov, coauthor of the study and a theoretical physicist at NIST, said: "Quantum simulations are widely believed to be one of the first useful applications of quantum computers. After perfecting these quantum simulators, we can then implement quantum circuits and eventually quantum-connect many such ion chains together to build a full-scale quantum computer with a much wider domain of applications."

It’s difficult to create larger quantum simulators as it becomes harder to keep track of and control more and more qubits. Jiehang Zhang, lead author and a postdoctoral researcher at the University of Maryland, believes that the system can be refined to fit 100 ion qubits or more. At that point, scientists can potentially model more difficult problems in “quantum chemistry or materials design," Zhang concluded. ?


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