#### Room 117

#### Universal decoherence due to gravitational time dilation

#### Himanshu Badhani

##### IMSc

*The physics of low-energy quantum systems is usually studied *

without explicit consideration of the background spacetime. Phenomena

inherent to quantum theory in curved spacetime, such as Hawking

radiation, are typically assumed to be relevant only for extreme

physical conditions: at high energies and in strong gravitational

fields. Here we consider low-energy quantum mechanics in the presence

of gravitational time dilation and show that the latter leads to the

decoherence of quantum superpositions. Time dilation induces a

universal coupling between the internal degrees of freedom and the

centre of mass of a composite particle. The resulting correlations

lead to decoherence in the particle position, even without any

external environment. We also show that the weak time dilation on

Earth is already sufficient to affect micrometre-scale objects.

Gravity can therefore account for the emergence of classicality and

this effect could in principle be tested in future matter-wave

experiments.

Ref: Nature Phys 11, 668–672 (2015) doi:10.1038/nphys3366

Link: www.nature.com/articles/nphys3366

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