The Building Blocks of a Quantum Computer
What aspects do you think make the scaling of number of qubits something difficult to achieve?
Nowadays scaling is being limited by things like design, temperature and wiring. For example, even though signal amplificators are equipment widely used, these are not commonly used at cryogenic temperatures (~5K). Research on them still needs to be done (cryo-CMOS Circuits and Systems for QuantumComputing Application).