A General and Modular Approach for Solid-State Integration and Readout of Zero-Dimensional Quantum Systems and Molecular Qubits

Electronic spectroscopy of zero-dimensional (0D) quantum systems, including point defects in solids, atomic states, and small molecules, is a critical tool for developing a fundamental understanding of these systems, with applications ranging from solid-state and molecular materials development to emerging technologies rooted in quantum information science. However, scanning-tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) techniques for accessing this regime are powerful but not scalable, while device-based approaches that rely on embedding these systems within a solid-state tunnel junction are not generally applicable, requiring bespoke solutions for integrating each 0D system with a given host and excluding large classes of candidate quantum systems. Here, we present the demonstration of an all-electrical readout mechanism for these quasi-0D states that is modular and general, dramatically expanding the phase space of accessible quantum systems and providing an approach that is amenable to scaling and integration with other solid-state quantum technologies. Our approach relies on the creation of high-quality tunnel junctions via the mechanical exfoliation and stacking of multi-layer graphene (MLG) and hexagonal boron nitride (hBN) to encapsulate the target quantum system (QS) in a MLG/hBN/QS/hBN/MLG heterostructure. This structure allows for electronic spectroscopy and readout of candidate quantum systems through a combination of Coulomb and spin-blockade, providing access to entire classes of quantum system that have previously only been accessible via optical spectroscopy or magnetic resonance measurements of large ensembles, if at all. As a demonstration of this approach, we report tunneling spectroscopy of vanadyl phthalocyanine (VOPc), a spin ½ molecular qubit that has demonstrated long coherence times and is compatible with standard evaporation techniques. Electronic spectroscopy of the MLG/hBN/VOPc/hBN/MLG heterostructure reveals resonances that quantitatively agree with tunneling spectroscopy obtained via STS of HOPG/hBN/VOPc half-devices.<br/><br/>*This work is supported by NSF QII-TAQS award OMA-1936219 and MPS-1936219, NSF NRT-QISE award DGE-2244045, and NSF MRSEC award DMR-2011876.