This is because it relies on a superconducting device called a Josephson junction to produce the qubits, in the form of specially tweaked electrons that are stable only at such low temperatures.
In their quest to build a computer that would take advantage of the weirdness of quantum mechanics, physicists are pursuing a number of disparate technologies, including superconducting devices, photon-based systems, quantum dots, spintronics and nuclear magnetic resonance of molecules.
