A MICROBE that thrives in one of the most inhospitable environments on Earth might just help engineers to build the first quantum computers.
The highly organised building skills of a protein manufactured by the microbe, which lives in scalding, sulphurous geothermal springs, has allowed NASA scientists to create regular arrays of 鈥渜uantum dots鈥�.
A quantum dot is a speck of gold or semiconductor material just a few nanometres across that can confine an electron in a space so small that its quantum behaviour wins out over its classical behaviour. Quantum dots like these could form the basis of minute chemical sensors, because the electrons鈥� quantum states change when molecules bind to the dots. But there are potentially more exotic applications over the horizon: quantum computers.
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Physicists believe that the quantum states of the electrons can be used as quantum bits 鈥� or qubits 鈥� for encoding data in a superfast quantum computer. Because the electron trapped in a quantum dot can be in several quantum states at once, a group of them could be harnessed to carry out many calculations simultaneously.
One of the main challenges in creating a quantum computer is working out how to process fragile quantum states without destroying them. Some strategies involve using photons to probe and change an electrons鈥� quantum state, but the quantum dots have to be arranged in regular arrays to make it possible to read each one. Now Andrew McMillan and Jonathon Trent at the NASA Ames Research Center in California say they may have found a way to do this.
The key lies in doughnut-shaped protein molecules that arrange themselves into large, flat sheets. The NASA researchers realised that quantum dots trapped in the 鈥渄oughnut holes鈥� would be lined up in the regular arrays they are looking for. The protein belongs to a family known as the chaperonins, whose usual task is to monitor the correct folding of other proteins. It comes from an 鈥渆xtremophile鈥� archaebacterium called Sulfolobus shibatae which lives in hot, acidic water of geothermal springs.
The natural protein, however, does not trap quantum dots. To make it do this, the researchers needed to align a 鈥渟ticky鈥� cysteine amino acid unit with the central hole. They did this by altering the gene for the protein and splicing it into the DNA of E. coli, which then manufactured the modified protein.
Heating the E. coli destroyed all its proteins except the extremophile鈥檚 modified chaperonin 鈥� which is highly heat resistant. The researchers were able to collect and purify the protein in the form of crystals up to 20 micrometres across, containing tens of thousands of molecules in a regular array.
They then repeatedly washed a slurry of gold or semiconductor particles over the protein crystals. Sure enough, when they rinsed and dried the crystals, an electron microscope revealed that the particles had fallen neatly into most of the holes.
The NASA team hopes to apply the same self-organising method to engineer other nanoscale computer components. One possibility might be to trap magnetic particles in the crystal to form a molecular-scale memory. David Goldhaber-Gordon, who studies quantum dot engineering at Stanford University, thinks the NASA work may be useful in helping build nanoscale circuits 鈥� perhaps planting connectors in the doughnut holes and linking them with nanowires.
