Seminar Erik Gauger – University of Copenhagen

Seminar Erik Gauger

Design principles for quantum-enhanced photocells inspired by biological systems 

Quantum biology offers intriguing insights into the interplay of coherent quantum dynamics and strong environmental coupling.  Taking inspiration from the processes and molecular structures underlying natural photosynthesis, I will discuss design principles for biologically-inspired artificial photocells, arguing that a carefully designed interplay between dissipative and coherent dynamics may unlock non-classical performance in solar energy harvesting.

Re-emission of absorbed photons is an important factor in the Shockley Queisser limit on the efficiency of conventional photovoltaic devices. Quantum interference between two optical dipoles enables "dark-state protection", where an excitation is stored until its energy has been converted into a longer-lived form. I will show that this concept applies to wide classes of non-identical organic molecular dimers identified by high throughput screening of a quantum chemistry database [1]. Rather surprisingly, our analysis shows that these messier asymmetric dimers can even outperform the idealised case [2] under realistic constraints.

Beyond dimers, larger numbers of coherently coupled nanostructures with a highly symmetrical geometrical arrangement can unlock “superabsorption" – the inverse phenomenon to superradiance – when placed in a structured photonic environment [3]. Alternatively, considering messier ring-like systems subject to additional dissipation from a condensed matter environment leads to another effect featuring excited states that cannot decay optically but which are ready to absorb further photons. This "optical ratcheting" could serve as a buffer for a stream of incident thermal photons arriving with a random distribution of arrival times [4].

[1] Photocell optimisation using dark state protection A. Fruchtman et al, Physical Review Letters 117, 203603 (2016)

[2] Efficient Biologically Inspired Photocell Enhanced by Delocalized Quantum States C. Creatore et al, Phys. Rev. Lett. 111, 253601 (2013).

[3] Superabsorption of light via quantum engineering, K. D. B. Higgins et al, Nature Communications 5:4705 DOI: 10.1038/ncomms5705 (2014).

[4] Quantum-enhanced capture of photons using optical ratchet states, K. D. B. Higgins, B. W. Lovett, E. M. Gauger, arXiv:1504.05849.