We have numerically investigated the effect of an underdamped intra-pigment vibrational mode on an exciton's quantum coherence and energy transfer efficiency. Our model describes a bacteriochlorophyll a pigment-protein dimer under the conditions at which photosynthetic energy transfer occurs. The dimer is modeled using a theoretical treatment of a vibronic exciton, and its dynamics are numerically analyzed using a non-Markovian and non-perturbative method. We examined the system's response to various values of the Huang-Rhys factor, site energy difference, reorganization energy, and reorganization energy difference. We found that the inclusion of the intra-pigment vibronic mode allows for long-lived oscillatory quantum coherences to occur. This excitonic coherence is robust against static site-energy disorder. The vibrational mode also promotes exciton transfer along the site-energy landscape thus improving the overall energy transfer efficiency.

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The noise and complexity inherent to quantum communication networks leads to technical challenges in designing quantum network protocols using classical methods. We address this issue with a hybrid variational quantum optimization framework (VQO) that simulates quantum networks on quantum hardware and optimizes the simulation using differential programming. We maximize nonlocality in noisy quantum networks to showcase our VQO framework. Using a classical simulator we investigate the noise robustness of quantum nonlocality. Our VQO methods reproduce known results and uncover novel phenomena. We find that maximally entangled states maximize nonlocality in the presence of unital qubit channels, while nonmaximally entangled states can maximize nonlocality in the presence of nonunital qubit channels. Thus, we show VQO to be a practical design tool for quantum networks even when run on a classical simulator. Finally, using IBM quantum computers we demonstrate that our VQO framework can maximize nonlocality on noisy quantum hardware. In the long-term, our VQO techniques show promise of scaling beyond classical approaches and can be deployed on quantum network hardware to optimize network protocols against their inherent noise.

after joining the department in 2018. His research interests include distributed processing of quantum information, entanglement theory, and general quantum resource theories.Ian George received the B.A. degree in physics and philosophy from Kenyon College, Gambier, OH, USA, in 2018, and the M.Sc. degree in physics (quantum information) from the University of Waterloo, Waterloo, ON, Canada, in 2020. He is currently pursuing the Ph.D. degree in electrical and computer engineering with the