https://techmonitor.ai/emerging-tech/towards-quantum-internet

It’s important to realise that the cat inside the box is both alive and dead, the physicist Erwin Schrödinger told a (presumably bemused) Albert Einstein in 1935. As a way of explaining the principle of quantum superposition, wherein any particle can possess two or more quantum states, Schrödinger imagined a cat – representing said atomic particles – inside a closed box with a Geiger counter and a flask of poison. If the dial on the counter begins to twitch at any point, the flask is broken and the poison presumably kills the cat. However, since the particles can exist in multiple states at once, the cat is actually both alive and dead until the box is opened, when one of either state is confirmed.

Such is the principle underlying how quantum computers work. Unlike a classical computer, in which bits that can either represent 0 or 1 are the basic unit of calculation, a quantum computer uses qubits, which can individually represent 0 or 1 simultaneously. This makes it much more efficient at processing complex calculations, but also incredibly hard to build. Not only is the stability of quantum computers dependent on running them at extreme conditions, including ultra-low temperatures (a recent working demonstration at -272°C was considered a breakthrough), there is also an inherent limitation to how many qubits can be harnessed by an individual machine.