I would like to ask about the need of a low temperature for the operation of superconducting qubits. I know a superconducting qubit is made from basically a LC circuit and Josephson junction. So obviously, since Josephson junctions are made from superconducting materials, it needs a low temperature to function.
However, as stated in the link (Would an ambient-pressure, room-temperature superconductor eliminate the need for a dil-fridge in transmon processors?), a low temperature is required not only for it to be superconducting but for it to reduce noises and protect the qubits from collapsing.
Does this mean that superconducting qubits have relatively shorter coherence time and susceptible to noises compared to other qubits like photon based ones, which can be used at RT?
Also, relating to this, I am guessing that a low temperature is required to keep the system quantum like explained here (How do we know that a superconducting circuit is a quantum system?). Is this correct? The energy separation of superconducting qubits is relatively small corresponding to the microwave range, but can you engineer the energy separation? Why does the current qubit uses microwave not other optical region?
