Quantum Mind? Can't Do Without the Classical express
Intelligent action begins with a plan. Just as an architect needs blueprints to evaluate options, any agent with will needs to repeatedly copy data about reality. But quantum mechanics forbids exact copying of unknown states — the fundamental theorem was discovered by Wojciech Zurek and William Wootters. A purely quantum object cannot preserve a 'snapshot' of its environment, nor compare alternative future scenarios.
You can try to copy approximately, but the quality drops below the level suitable for reliable decisions. Even executing a chosen step is hindered by the linearity of quantum equations: you can't simply single out one outcome from a multitude of superimposed probabilities. An architect in the quantum world is left without a pencil that wouldn't break with every attempt to sketch a blueprint.
The conclusion is striking: reason, will, and goal-directedness require classical 'parts' — they act as a rigid stage with clear boundaries, like spacetime curvature or the speed of light limit, against which the drama of choice unfolds. Most unexpectedly, this no-cloning prohibition is not a bug but a safeguard. It guarantees the inviolability of quantum information, paving the way to absolutely secure communication.
Original abstract
as written by the authors arXiv:2510.13247
What are the physical requirements for agency? We investigate whether a purely quantum system (one evolving unitarily in a coherent regime without decoherence or collapse) can satisfy three minimal conditions for agency: an agent must be able to create a world-model, use it to evaluate the likely consequences of alternative actions, and reliably perform the action that maximizes expected utility. We show that the first two conditions conflict with the no-cloning theorem, which forbids copying unknown quantum states: world-model construction requires copying information from the environment, and deliberation requires copying the world-model to assess multiple actions. Approximate cloning strategies do not permit sufficient fidelity or generality for agency to be viable in purely quantum systems. The third agency condition also fails due to the linearity of quantum dynamics. These results imply four key consequences. First, agency requires significant classical resources, placing clear constraints on its physical basis. Second, they provide insight into how classical agents emerge within a quantum universe. Third, they show that quantum computers cannot straightforwardly simulate agential behavior without significant classical components. Finally, they challenge quantum theories of agency, free will, and consciousness.
The no-cloning theorem states: it is impossible to create an exact copy of an arbitrary unknown quantum state. This is not a technical limitation but a fundamental law of nature.
In science fiction, the idea of quantum consciousness appears frequently (for instance, in Hannu Rajaniemi's novel 'The Quantum Thief'), but new results show that without a classical component, no quantum 'thinking' is possible.