Atomically Engineering Potential Landscapes: From Defect Emitters towards Entangled Quasiparticles

Defects are often perceived as imperfections, but in the realm of two-dimensional (2D) materials, they can be precisely engineered to create and control entirely new quantum phenomena. We hypothesize that achieving atomic-scale control over heterostructure design allows us to define the potential landscape for electrons at their native length scale, thereby dictating the symmetry of the potential and the resulting electronic interactions. This precise tailoring of the potential offers a critical mechanism for steering the behavior of emergent quasiparticles??"such as excitons, polaritons, or more exotic species such as Tomonaga-Luttinger liquids??"which arise from collective interactions in solids.

To validate this approach, we leverage 2D, 1D and 0-D heterostructures, combined with advanced scanning probe microscopy techniques, to directly probe and manipulate these excitations. In this talk, I will detail our work on point defects in materials like MoSe ₂ and WS ₂ , demonstrating how these can be engineered into quantum emitters capable of single-photon emission. Using photo-assisted Scanning Tunneling Microscopy (photo-STM) and high-throughput theoretical modeling, we have identified and experimentally validated substitutional defects (e.g., C, Co, Yb substituting sulfur atoms in WS ₂ ) that function as atomically precise two-level systems, analogous to color centers. This level of control, creating atomically identical quantum emitters have direct implications on technological advances in terms of next generation quantum sensors and potential entangled photon sources, as well as exploring fundamental properties of many body quantum systems. To achieve this control and to directly map the emission on the atomic scale and start deciphering the interaction of these quantum emitters with their surrounding required substantial development of THz Scanning Tunneling Microscopy, gate assisted Scanning Tunneling Luminescence eventually coupled to quantum optics detection schemes and novel hyperspectral electronic structure mapping techniques which I will mention as well. Ultimately, we are able to create excitons with atomic precision and hence correlate unambiguously surface morphology, electronic structure and optical emission properties with atomic precision. This approach we recently leveraged to visualize the emission from Moire structures at its native length scale together with Feng Wang.

Building on these achievements, I will outline the next frontier which is understanding the theoretical and experimental strategies required to understand the decoherence pathways affecting individual emitters, devise methods to coherently couple atomically identical defects, and assess the technological impact of creating entangled color centers. Ultimately, I argue that controlling quantum effects in matter on the length scale of individual quantum states is one of several catalysts to start thinking about quantum engineering as its own distinct discipline.

Speaker: Alexander Weber-Bargioni, Lawrence Berkeley National Laboratory