Have a look at "Quantum Computing: Fundamentals, Implementations and Applications " by Bhat et al. from 2022 https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9783210

It's kind of a crappy paper and the explanations are mediocre at best, but it provides a decent survey of the main physical implementations in language that is simple to follow.

Just like a physical bit, qubits are basically an abstraction over an analog world; they can be implemented in any physical medium you can make a quantum measurement with.

Most current implementations are "trapped ion" computers. This is exactly what it sounds like, an ion trapped in an electromagnetic field. However, people are working on many systems, including:

- Photonic (photon) - Superconducting (Cooper pair) - Diamond/silicon carbide (single dopant) - Liquid NMR (molecular spin)