Biocomputers – an alternative to quantum computing?

Slime mould's ability to solve complex route planning tasks is a reminder that biocomputers could offer an alternative to quantum computing.
5 April 2023

Pathfinding technology: slime mould (Physarum polycephalum) can solve complex route planning problems and has been used to simulate transport networks and migration routes. Image credit: Shutterstock Generate.

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Quantum computing as a service (QCaaS) makes it possible for users to access qubit-enabled information processing architecture over cloud services. Qubits use real-world physics to tackle problems that are hard or even impossible to solve using the classical bits found in conventional computing machines. But when it comes to finding solutions for complex route planning tasks, users may want to consider an alternative to quantum computing. And that alternative, if you missed the biocomputing boom that occurred a decade or so ago, could come as quite a surprise.

Today’s quantum processors are dubbed noisy intermediate-scale quantum (NISQ) technology. The endgame is to create fault-tolerant quantum devices featuring a million or more physical qubits, which can be turned into logical qubits using error correction methods. Quantum computing states can be extremely fragile and sensitive to their surroundings. And today, developers have to work hard to support measurements involving just a few hundred qubits, let alone millions.

Early success stories include the use of quantum computers to solve supply chain and logistics problems. But the technology comes at a price and has collectively required billions of dollars to develop. However, it turns out that nature has been busy, too, developing organisms with biocomputing properties. And one of its brightest stars can be found in the forest, which goes by the Latin name Physarum polycephalum, also commonly known as slime mould.

A biocomputing Swiss army knife

Visible with the naked eye, the bright yellow-coloured, single-celled organism adapts its growth based on surrounding conditions. Slime mould is attracted by nutrients such as oat flakes, deterred by repellents such as salt, and capable of avoiding hazards. Dubbed wetware, Physarum polycephalum combines hardware and software capabilities. And, to the delight of researchers, the biomaterial can be used to solve mazes and determine the shortest path between nodes in a network – a notoriously difficult problem for classical computers to answer efficiently.

“The ease of culturing and experimenting with Physarum makes this slime mould an ideal substrate for real-world implementations of unconventional sensing and computing devices,” writes Andrew Adamatzky, director of the Unconventional Computing Laboratory within the Department of Computer Science at UWE. “In the last decade, Physarum has became a Swiss army knife of unconventional computing: give the slime mould a problem and it will solve it.”

And if you doubt the ability of slime mould to offer an extremely affordable and resource-efficient biocomputing alternative to quantum computing, it’s worth checking out some of the organism’s achievements in the lab. Adamatzky and his colleagues have found particular success in allowing the mould to explore miniature replica terrains, highlighting regions of interest with nutrients that set growth parameters for the living network.

The 3D landscapes formed in Nylon sit above petri dishes of water, which make low areas more desirable for the mould due to the higher humidity. And the conditions mean that the organism spreads out its protoplasmic tubes in a way that mimics the growth of transport networks – for example, by routing around mountainous areas. Researchers have shown how slime mould can reproduce the route of Germany’s longest autobahn and giant road networks across the US; motorways in the Netherlands, Belgium, France and the UK; and even the Tokyo railway system.

Solving the travelling salesman problem

Slime mould’s ability to solve complex route planning, points towards the biocomputing material as being an alternative to quantum computing. The issue with route planning is that problems become exponentially harder for conventional computers to solve with each node added to the network. But both quantum computers and organisms such as Physarum polycephalum are capable of selecting the optimal (or at least close to optimal) path in linear time, although only slime mould is able to achieve the feat at such an incredibly low price point. And its remarkable capabilities don’t just stop there.

In an extremely clever experiment, scientists demonstrated the capacity of slime mould to anticipate events. Researchers exposed the organism to regular bursts of cold air blown using a fan, which paused its growth. And the team noticed that over time the mould became used to the timings and paused its growth in anticipation even when the fan wasn’t activated. It’s often said that quantum computers exhibit spooky behaviour thanks to the physics of entangled qubits, but slime mould appears to have some eerie properties of its own.

Today, analysts are using digital models of slime mould to translate its ability to form efficient networks across a range of applications, including optimizing the parameters of photovoltaics. But the amoeba’s physical properties turn out to be useful as well. Adamatsky and his team have shown how slime mould can be integrated with electrodes to produce wires that have self-healing properties. There appears to be no end to the appeal of this organism, which is even the subject of a feature-length cinema release named ‘The creeping garden’.

If you have a few oat flakes to hand, a petri dish and access to a 3D printer to create a terrain, you could be well on the way to exploring whether biocomputers really are an alternative to quantum computers.