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Quantum information: Microwave quantum computer Microwaves, familiar from our everyday lives, can be used to perform quantum computation. We show how this is possible using a quantum electronic device called a Josephson Travelling Wave Parametric Amplifier, or TWPA for short. This device has already been made and extensively tested in the lab for the purpose of amplifying extremely weak signals. We here demonstrate that the TWPA is much more than just an amplifier: It is a remarkably powerful resource for generating just the type of entanglement that is needed for a quantum computer. Surprisingly, a full-fledged universal quantum computer can be made using just four such devices, if their output radiation is combined to interfere in just the right way. This proposal may lead to small-scale quantum computers using already existing technology.