Most electrical circuits use copper at room temperature to conduct electricity. Applications include large power transmission and precise electronics. These circuits have resistance, and that’s not a bad thing. Resistance is important for designing circuits, controlling current flow and voltage levels. But something weird happens when circuits use superconducting materials and are cooled to near absolute zero: the resistance magically disappears (confession: it’s not really magical).
Superconducting materials are not yet common, but no energy loss with DC and ultra small energy loss with AC are benefits causing these materials to find their ways into more and more applications. They are found in high-current devices, including Magnetic-Resonance Imaging (MRI), fusion power, and wind turbines. They are also found in applications where ultra-low noise (electric loss leads to electrical noise) and extreme precision are required, including radioastronomy, quantum computing, and metrology.
These materials allow the development of devices that would otherwise be impossible, such as the Josephson junction, which is fundamental to fabricating many types of superconducting qubits. These junctions enable superposition and entanglement. Superconducting circuits behave like artificial atoms, with discrete energy levels that allow the control and transformation of quantum states. Furthermore, stable qubits require energy to not be lost as heat, which resistance-free conduction allows.