Electrical current flows through electrical circuits like water through a pipe. However, this “pipe” isn’t actually hollow. It is, in fact, a conductive material, usually metallic, that consists of atoms. The electrons in the electrical current pass from atom to atom, but they also collide with some atoms along the way. These collisions with atoms result in the transfer of kinetic energy away from the electrons, thus slowing the electrons down. This is known as “resistance.”
The amount of electrical resistance that the electrons encounter depends on the length, cross-sectional area, and temperature of the conductor. We often add resistance to electrical circuits intentionally in order to direct the flow of current, protect against surges in voltage, allocate correct voltages, and more.
But something interesting happens when a conductor is cooled below what is called its transition temperature. The material now conducts electricity with zero resistance, a phenomenon known as superconducting.
Without resistance, the electrical current in a loop can continue indefinitely without a power source and without loss to heat. This usually happens at temperatures close to absolute zero, however materials have been discovered that transition at relatively high temperatures. And although superconduction does not generate heat, it does, however, generate exterior magnetic fields. These magnetic fields allow the emergence of superconducting qubits and superconducting quantum computing.
A qubit is the fundamental unit of quantum information, and quite a few modalities are currently being researched and developed. A superconducting computer uses these superconducting loops as its qubits. They exhibit the behavior of atoms, and are thus often referred to as “artificial atoms.” A superconducting qubit can be in a ground state, an excited state, and up until measurement, a superposition of both states. Some are capable of being in higher excited states, although they become known as qutrits or qudits at those levels.
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Although superconducting qubits offer a number of advantages over other modalities, they also face some significant challenges.
Some of the advantages are:
And some of the challenges are:
Because they use existing technologies, superconducting quantum computers are probably the most abundant. And with size measured in qubit counts, they are the second largest quantum computers, behind only neutral atom quantum computers. However, two of the above challenges are particularly significant. First, superconducting qubits or their wiring can be so defective that they outright fail. And, second, the shielding they require is physical, which makes superconducting quantum computers the second largest physically, behind ion trap quantum computers.