As far as I understand, transforming and maintaining states of qubit devices in quantum computers is associated with all sort of problems such as transformation errors and decoherence. At the same time, quantum mechanics describes states of a quantum system always relatively to the basis states of some measurement apparatus. This implies that, at least in principle, it should be possible to transform the measurement system, rather than the qubits, in performing "quantum" computation. The advantage of this approach would be that measurement instruments are macroscopic, can be controlled by classical computers, and can be described by laws of classical physics accurately. In fact, this line of reasoning suggests that some form of computing based on classical physics should be equivalent to quantum computation. So, here is my question: Is there anything wrong with this logic? Did anyone pursue this reasoning to try to construct classical analogs of quantum computers?

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    $\begingroup$ Welcome to QCSE. We can say in some instances that we "measure in the Hadamard basis" which is equivalent to "performing a Hadamard gate and then measuring in the computational basis". For example, we can physically rotate a polarizing filter or a Stern-Gerlach machine. Alternatively, you might want to research measurement-based quantum computing (MBQC), but that topic is also pretty advanced for new learners now. Either way, we always suffer the slings and arrows of decoherence. $\endgroup$ Nov 10, 2023 at 14:25


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