Prineha Narang1
Harvard University1
The potential impact of active solid-state quantum defects, frequently referred to as artificial atoms in solids, on creating quantum information systems in the near-term is evident <sup>1,2</sup> <sup>3</sup> . Yet, design and control of multiqubit systems and robust quantum interfaces to these defects at the nanoscale has remained challenging. While there are computational methods and measurement techniques that can study a single solid-state spin qubit based on defects in solids, understanding the interaction between them remains a major challenge. In this context, I will introduce the crucial chemical degree of freedom to the state-of-the-art in quantum defects by demonstrating how these “artificial atoms” become “artificial molecules” when placed within a few angstroms of each other. At these length scales, the host lattice is not only a passive dielectric that screens interactions between defects in complexes, but actively participates in structure relaxation and determines configuration-dependent interactions. Armed with this physical understanding, I will demonstrate how this chemical degree of freedom can be used to tune quantum defects. Next, I will present promising physical mechanisms and device architectures for coupling such quantum defects to other qubit platforms <i>via</i> dipole-, phonon-, and magnon-mediated interactions. Specifically I will share our latest work on coupling magnons to magnetic emitters as a natural step towards magnon-mediated efficient manipulation of spin-qubit states with applications in sensing and quantum information science. I will discuss a scheme that uses magnetic nanoparticles that sustain antenna-like magnon resonances as nanomagnonic cavities for microwave magnetic fields. Here, in recent work we have shown that nanomagnonic cavities can modify the local magnetic environment of spin emitters in the microwave domain, facilitate the magnetic drive of spin transitions, and allow for strong coupling of these emitters with single magnons<sup>4</sup>. I will show how the magnetic fields of nanomagnonic cavities that change spatially on the length scales of single molecular or defect emitters, coupled with descriptions of spin emitters beyond the point-dipole approximation, enables selection rule-breaking of orbital-spin transitions<sup>5</sup>. Such nanomagnonic cavities could pave the way towards magnon-based quantum networks and magnon-mediated quantum gates. Taking this further, I will present some of our recent work in capturing non-Markovian dynamics in open quantum systems (OQSs) built on the ensemble of Lindblad's trajectories approach <sup>6,7</sup>. In the outlook, I will discuss new approaches from quantum chemistry for OQSs that could guide the controllable coupling of active quantum defects and create robust quantum interfaces to the nanoscale.<br/> <br/>1. Awschalom, D. <i>et al.</i> Development of Quantum Interconnects (QuICs) for Next-Generation Information Technologies. <i>PRX Quantum</i> <b>2</b>, 017002 (2021).<br/>2. Head-Marsden, K., Flick, J., Ciccarino, C. J. & Narang, P. Quantum Information and Algorithms for Correlated Quantum Matter. <i>Chem. Rev.</i> (2020) doi:10.1021/acs.chemrev.0c00620.<br/>3. Philbin, J. P. & Narang, P. Computational materials insights into solid-state multiqubit systems. <i>PRX Quantum</i> <b>2</b>, (2021).<br/>4. Neuman, T., Wang, D. S. & Narang, P. Nanomagnonic Cavities for Strong Spin-Magnon Coupling and Magnon-Mediated Spin-Spin Interactions. <i>Phys. Rev. Lett.</i> <b>125</b>, 247702 (2020).<br/>5. Wang, D. S., Neuman, T. & Narang, P. Spin Emitters beyond the Point Dipole Approximation in Nanomagnonic Cavities. <i>J. Phys. Chem. C</i> <b>125</b>, 6222–6228 (2021).<br/>6. Head-Marsden, K., Krastanov, S., Mazziotti, D. A. & Narang, P. Capturing non-Markovian dynamics on near-term quantum computers. <i>Phys. Rev. Research</i> <b>3</b>, (2021).<br/>7. Krastanov, S. <i>et al.</i> Unboxing Quantum Black Box Models: Learning Non-Markovian Dynamics. <i>arXiv [quant-ph]</i> (2020).