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Fluctuation phenomena in nanoscale quantum optical systems

Fluctuation-induced phenomena are a fascinating and fundamental feature of quantum electrodynamics (QED), with implications spanning spontaneous emission of atoms, decoherence of macroscopic quantum superpositions, stability of colloidal suspensions such as milk, adhesive properties of gecko feet, stiction in nano- and micro-mechanical machines, and, potentially, the accelerated expansion of the universe.

My research involves coming up with ways to engineer fluctuation-induced forces, dissipation and decoherence in nanoscale quantum optical systems.  From an open quantum systems perspective, one can see that a few ways to tailor fluctuation phenomena are:

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  • Modifying the boundary conditions (e.g., optical, material properties, geometry) to modify the bath spectral density

  • Modify the form of coupling between the system and the bath, for example electric vs magnetic interactions

  • Drive the system to a suitable non-equilibrium state

  • Use correlations internal to the system to modify the effective system-bath interaction

 

This is by no means an exhaustive list, but these are some of the ways that I have poked at the problem of engineering fluctuation phenomena in nanoscale quantum systems.

Collective effects and Non-Markovian dynamics 

The interference between coherent radiation processes in an ensemble of atoms leads to collective effects, as first illustrated by Dicke super- and subradiance. Collective effects are responsible for a variety of phenomena, relevant in fundamental and applied physics. They can enhance atom-light coupling strengths, which finds applications in quantum information processing, or can be used to selectively decouple a system from its environment, improving the storage and transfer of quantum information. Moreover, collective dipole-dipole interactions, which are responsible for energy exchange between the emitters, can lead to modifications of chemical reactions.

I am interested in studying collective effects in atom-field interactions in non-Markovian regimes where the memory effects of the electromagnetic environment can no longer be forgotten. From a simplistic comparison of system and bath time scales in an open quantum system schematic, one can see a few ways a composite system of two subsystems interacting with a common bath can exhibit non-Markovian dynamics:

  • In the presence of strong coupling between the system and the bath the bath degrees of freedom are more memoryful

  • In the presence of retardation, one needs to take into account the intermediary bath degrees of freedom that communicate information between the two parts of a composite/collective system

  • In the presence of slow modes of the bath, such as near a photonic band edge, where the bath modes get to spend additional time interacting with the system

I am interested in exploring the above different origins of non-Markovian dynamics, and developing quantitative measures of non-Markovianity based on physically intuitive ways of understanding non-Markovian atom-field interactions.

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