Austrian Scientists Develop Ghostly Superposed Quantum Circuits for Faster Quantum Computing
Scientists at the University of Vienna and the Austrian Academy of Sciences have developed a new quantum computing technique in which operations occur without a well-defined order. The new technique accomplished a task more efficiently than a standard quantum computer, and could open the way to faster quantum computing.
The study is published in Nature Communications with the title “Experimental superposition of orders of quantum gates.” The paper is freely available online.
Quantum Gates Applied in Different Orders at the Same Time
Quantum computers encode information in “qubits” that can be in a weird quantum superposition of zero and one states, and therefore they can process information in ways that have no equivalent in classical computing by exploiting subtle quantum phenomena such as quantum entanglement.
The Austrian researchers, led by Philip Walther and Caslav Brukner, introduced even more quantum weirdness by allowing the quantum circuitry itself – the logic gates that operate on the qubits – to be in a superposition of states.
In the usual approach to quantum computing, quantum gates are applied in a specific order, one gate before another. But it was recently realized that quantum mechanics permits ghostly quantum circuits with superposed quantum gates.
“Quantum computers achieve a speed-up by placing quantum bits (qubits) in superpositions of different states,” say the researchers. “However, it has recently been appreciated that quantum mechanics also allows one to ‘superimpose different operations’.”
The new resource we exploit can be interpreted as a superposition of causal orders, and could allow quantum algorithms to be implemented with an efficiency unlikely to be achieved on a fixed-gate-order quantum computer.
This means that a set of quantum gates could act in all possible orders at the same time. For example, two quantum logic gates A and B can be applied in both orders at the same time. In other words, A acts before B and B acts before A. The researchers designed and performed an experiment – the first to implement a superposition of quantum gates in the lab – in which two quantum logic gates were applied to single photons in both orders.
The effect can be used to reduce the total number of gates required for certain quantum computations, and therefore perform the computations faster.
Quantum computers may theoretically be able to solve certain problems – including code breaking – much faster than classical computer and perform computations that would be otherwise impossible. This explains the enthusiasm of researchers, venture capitalists, and the intelligence community. Further research on superposed quantum gates could permit building quantum computers of even higher performance.
Using the popular “explanation” of how a quantum computer works illustrated by venture capitalist Steve Jurvetson in this video – a quantum computer uses the computational resources of parallel universes – it’s tempting to think of different quantum computers in parallel universes, each with its own ordered arrangement of quantum gates, performing a computation in parallel and delivering the result faster than a single quantum computer. However, quantum physics is counter-intuitive and “visual” explanations should be taken with caution.
Images from Philip Walther Group, University of Vienna, and Pixabay.