Several technologies are being explored for qubit implementation, each featuring its advantages and challenges. Superconducting qubits with Josephson junctions afford the maintenance of quantum coherence at ultra-low temperatures, exemplified by Google’s Sycamore processor that is said to have demonstrated quantum supremacy over classical systems.
To maintain such low temperatures, however, there is a big challenge. Ions as qubits are manipulated by electric and magnetic fields and possess long coherence times allowing for complex operations to occur before decoherence.
They are slow at gate formation and in scaling up. Photonic qubits employ polarizations and some such properties, operate at room temperature, and are best for quantum networking as they are compatible with optical communication systems. They suffer with gate fidelity due to multi-photon entanglement.
Being a theory as yet, topological qubits can promise error-resistant quantum computing in view of their topological nature. If somehow realized, topological qubits could reduce to a very great extent the error correction needs of other forms of qubits, although till now no actual topological qubits have been demonstrated.
