09 Sep

A quantum computer has been successfully simulated within a standard computer by scientists at Linköping University.

While few useful algorithms are currently available for quantum computers, it is expected that the technology will eventually be hugely significant for simulating biological, chemical and physical systems that are too complicated for even the most powerful computers available today.

A single bit in a computer can take only the value one or zero, but a quantum bit can take all values in between. This means that quantum computers do not need to take as many operations for each calculation they carry out.

“Our results should be highly significant in determining how to build quantum computers,” said professor Jan-Åke Larsson (pictured above).

“We have shown that the major difference is that quantum computers have two degrees of freedom for each bit. By simulating an additional degree of freedom in a classical computer, we can run some of the algorithms at the same speed as they would achieve in a quantum computer.”

The team constructed a simulation tool, Quantum Simulation Logic (QSL) that enables them to simulate the operation of a quantum computer in a classical computer. The tool contains the primary property that sets quantum computers apart from current machines: one extra degree of freedom for each bit that is part of the calculation.

“Thus, each bit has two degrees of freedom. It can be compared with a mechanical system in which each part has two degrees of freedom: position and speed. In this case, we deal with computation bits, which carry information about the result of the function, and phase bits, which carry information about the structure of the function,” Jan-Åke Larsson explained.

They have used the simulation tool to study some of the quantum algorithms that manage the structure of the function. Several of the algorithms run as fast in the simulation as they would in a quantum computer.

“The result shows that the higher speed in quantum computers comes from their ability to store, process and retrieve information in one additional information-carrying degree of freedom. This enables us to better understand how quantum computers work. Also, this knowledge should make it easier to build quantum computers, since we know which property is most important for the quantum computer to work as expected,” Jan-Åke Larsson added.

The simulated computer has also been supplemented with a physical version built with electronic components and gates that are similar to those used in quantum computers.

It should allow students to simulate and understand how quantum cryptography and quantum teleportation works, as well as some of the most common quantum computing algorithms.

Plans are now afoot to build a Swedish quantum computer within ten years and the EU has designated quantum technology as one of its flagship projects.

In November 2018, Sussex University scientists said they made a “breakthrough” in quantum computing that could pave the way to commercialisation of the technology by making it useful outside of strict laboratory conditions.

E&T took an in-depth look at the potential of quantum computingearlier this year, in our quantum special issue. 

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