Loss of quantum coherence due to gravity Consider a particle which moving inside a gravitational field.Will it lose its quantum coherence?
According to GR , the particle will follow a geodesic but if it does then shouldn't its wavefunction have been collapsed?
But since there is nothing for the particle to interact with,it shouldn't lose its quantum coherence!How is this paradox resolved?
 A: 
Consider a particle which moving inside a gravitational field.Will it lose its quantum coherence?

In quantum physics, where the term "quantum coherence" can have a physics meaning, a single particle moving in an empty universe will not lose any coherence with itself, as it is the only thing in this universe.
A single particle moving in a gravitational field in quantum physics, needs a quantum mechanical solution for the state "particle in gravitational field", and , assuming gravity is quantized, it will not lose its coherence because one wavefunction will define its state.

According to GR , the particle will follow a geodesic but if it does then shouldn't its wavefunction have been collapsed?

GR is a classical theory, even if one describes the particle with a quantum mechanical wavefunction, suppose it is a hydrogen atom,, classical GR cannot interact with the wavefunction and induce a collapse, i.e. a different wavefunction to the system "gravity+hydrogen atom". If we assume the gravitational potential and solve for quantum mechanical bound states, again, one wavefunction will describe the particle and there is no way it can "collapse" . Actually quantum mechanical bound states of the neutron in the gravitational field of the earth have been measured experimentally.

But since there is nothing for the particle to interact with,it shouldn't lose its quantum coherence!How is this paradox resolved?

There is no paradox, you are just misinterpreting  classical and  quantum states.
