Simulating Open Quantum Systems with Molecular Spin Qudits

The ever-growing development of quantum computers recently allowed for public accessibility to noisy intermediate-scale quantum (NISQ) computers [1]. Now, a great effort of conceptualization and implementation of efficient quantum simulations is realizing the future envisioned by Feynman [2] in which we are finally able to tackle quantum phenomena which go beyond classical computation [3]. However, interaction with the environment typical of open quantum systems (OQS) represents a double-edged sword in such applications. On the one hand it is the primary cause of the "noisy" nature of nowadays quantum simulators, limiting the computational power of algorithms developed on such platforms. On the other hand, since most quantum systems of relevant interest are effectively OQS, quantum simulators are faced with the problem of simulating non-unitary time evolution together with the coherent Hamiltonian dynamics. This presents a significant challenge, since the dynamics of quantum computers is limited to unitary quantum gates.<br/><br/>In this work [4], we have demonstrated how molecular nanomagnets coupled to superconducting resonators form a flexible playground that allows the implementation of different algorithms to simulate OQS. The ability of molecules to host systems with many addressable levels (qudits) makes it possible to reduce the complexity of such algorithms both in the number of operations (gates) to be implemented and in the number of units required. Through detailed numerical simulations, we have studied two conceptually different algorithms to show the advantages and disadvantages of each, and simulated proof-of-concept models that we believe can be taken to the laboratory in the near future, showing that in all cases molecular nanomagnets are an optimal ingredient in the study of OQS by means of digital algorithms.<br/><br/><b>References</b><br/>[1] Preskill, J. (2018). Quantum computing in the NISQ era and beyond. <i>Quantum</i>, <i>2</i>, 79.<br/>[2] Feynman, R. P. (2018). Simulating physics with computers. In <i>Feynman and computation</i> (pp. 133-153). CRC Press.<br/>[3] Arute, F., Arya, K., Babbush, R., Bacon, D., Bardin, J. C., Barends, R., ... & Martinis, J. M. (2019). Quantum supremacy using a programmable superconducting processor. <i>Nature</i>, <i>574</i>(7779), 505-510.<br/>[4] Roca-Jerat, S., Macaluso, E., Chiesa, A., Paolo, S., Luis, F., Zueco, D. & Carretta, S. (2024). Simulating open quantum systems with molecular spin qudits. <i>In preparation</i>.