Unfortunately, it involved building an artificially intelligent observer and, even more problematically, that observer had to be a quantum computer, a device that exploits quantum mechanics to do huge numbers of calculations in parallel.

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But then there is another difficulty: making the components exactly the right size is even more crucial for a quantum-effect device than for a regular transistor.

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Listeners will need to employ a bit of imagination to match Johannsson's composition to the title "Melodia (Guidelines for a Space Propulsion Device Based on Heim's Quantum Theory), " but it's hard to deny the propulsion at work here.

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In addition, since a single electron travelling through the device emits light not once (as in most other lasers), but many times, quantum cascade lasers are powerful: Dr Capasso's group has recently shown that they beat conventional semiconductor lasers by a factor of 20.

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