# Coherence properties of the microcavity polariton condensate

Abstract: A theoretical model is presented which explains the dominant decoherence process in a microcavity polariton condensate. The mechanism which is invoked is the effect of self-phase modulation, whereby interactions transform polariton number fluctuations into random energy variations. The model shows that the phase coherence decay, g(1)(τ), has a Kubo form, which can be Gaussian or exponential, depending on whether the number fluctuations are slow or fast. This fluctuation rate also determines the decay time of the intensity correlation function, g(2)(τ), so it can be directly determined experimentally. The model explains recent experimental measurements of a relatively fast Gaussian decay for g(1)(τ), but also predicts a regime, further above threshold, where the decay is much slower.

## Summary (1 min read)

### Summary

- A theoretical model is presented which explains the dominant decoherence process in a microcavity polariton condensate.
- The mechanism which is invoked is the effect of self-phase modulation, whereby interactions transform polariton number fluctuations into random energy variations.
- This fluctuation rate also determines the decay time of the intensity correlation function, g(τ), so it can be directly determined experimentally.
- The model explains recent experimental measurements of a relatively fast Gaussian decay for g(τ), but also predicts a regime, further above threshold, where the decay is much slower.
- – Microcavity polaritons are quasiparticles arising from the strong coupling between excitons and photons confined in planar cavity structures.
- As in other quantum condensates, such as atomic gases or superconductors, a key property is the existence of an order parameter, the local phase, which is correlated over large times and distances.
- The authors theory shows that, under appropriate pumping conditions, existing microcavity structures should display much longer coherence times than currently measured, opening up opportunities for experiments manipulating the quantum state of the system.
- For the polariton condensate this function is directly revealed by coherence measurements on the optical emission [1,4,5].
- The discussion was limited to the case of slow number fluctuations, whose presence is directly evident in the experimental data.
- Here the authors show that this regime is achieved due to critical slowing down in the threshold region.
- At higher powers, where the critical slowing down disappears and fluctuations become faster, the authors predict that the phase coherence times will become significantly longer.

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##### Citations

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### Cites background or methods from "Coherence properties of the microca..."

...Fluctuations in the particle number lead to changes of the ground state energy because of repulsive polariton-polariton interactions and therefore destroy phase coherence [8]....

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...The above equation can also be derived using a quantum model of the polariton condensate [8]....

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94 citations

70 citations

### Cites background from "Coherence properties of the microca..."

...These experiments showed a Gaussian time dependence of the correlation function which can be explained [68] by considering the dynamics of condensate density fluctuations, which in turn produce energy shifts, reducing the phase coherence....

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...Again, such results have been reproduced by single mode models [68] and by quantum kinetic approaches [70]....

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##### References

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