Captivating Cavities

Article: Manipulating matter by strong coupling to vacuum fields published in Science by Francisco J. García-Vidal, member of Theoretical Condensed Matter Physics Department and IFIMAC researcher.

Laser technology is a familiar example of how confining light between two mirrors can tune its properties. Quantum mechanics also dictates that even without extraneous light, matter confined in a cavity resonant with its electronic or vibrational transitions can couple with vacuum electromagnetic field fluctuations. In this paper, Garcia-Vidal and co-workers review the remarkable and still somewhat mysterious implications of this “strong-coupling” regime.

Both experimental and theoretical studies have shown changes to photochemical reaction rates under strong coupling between the electronic excitations of molecules and cavity electromagnetic modes. Strong coupling modifies the shape of the potential energy surfaces associated with the excited states of the molecule, allowing for a manipulation of its photophysical properties. Moreover, ground-state chemical reactivity can also be completely modified when molecular vibrations are strongly coupled to infrared cavity modes. Although a detailed picture of the mechanism is still missing, symmetry seems to play a key role. Material properties can also be changed by strong coupling. Charge and energy transport in organic materials and magneto-conductivity in two-dimensional electron gases have been shown to be altered. Thanks to the intrinsic delocalized character of the polaritonic modes, transport properties can be then tuned at a macroscopic scale. It is also feasible to manipulate phases of matter by means of strong coupling. It has been reported that the critical temperature of a superconductor can be substantially enhanced by judiciously exploiting vibrational strong coupling and that the ferromagnetism of nanoparticles can be boosted by orders of magnitude. These examples illustrate the potential of using vacuum fields instead of intense laser fields to induce modification of material properties. [Full article]

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