There will always be stray air molecules and stray photons ricocheting off qubits, causing them to lose their quantumness and decohere into normal bits. This can be corrected but, for each qubit, this error correction requires anything from 10 to 100 qubits. A conventional computer develops an error--a 0 flipping to a 1 or vice versa--about once every trillion trillion operations. However, a quantum computer develops an error about once every thousand operations. This is a crippling rate and it is not yet certain that such error correction can, in practice, outpace the accumulation of errors.
Currently, the record-holding quantum computer, announced by IBM in November 2021, has 120 qubits. This is almost double the number of the previous record-holder that was built by Google. However, the number of qubits being quoted is deceptive since only a small portion of qubits are useable for calculations, while the rest are needed simply to correct the errors accumulating in those qubits. (p. 167)