A protocol for testing the quantum nature of large objects – that, in principle, could work for objects of any mass – has been proposed by researchers in the UK and India. A key feature of the protocol is that circumvents the need to create a macroscopic quantum state to test whether or not quantum mechanics is valid at large scales. Some physicists, however, are not convinced that the research constitutes a significant advance.

Quantum mechanics does a fantastic job of describing atoms, molecules and subatomic particles like electrons. However, larger objects usually do not display quantum behaviour such as  entanglement and superposition. This can be explained in terms of quantum decoherence, which occurs when delicate quantum states interact with noisy environments. This causes macroscopic systems to behave according to classical physics.

How quantum mechanics breaks down at macroscopic scales is not only theoretically fascinating but also crucial to attempts to developing a theory that reconciles quantum mechanics with Albert Einstein’s general theory of relativity. Physicists are therefore keen on observing quantum behaviour in ever-larger objects.

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