PCSI2027 Session PCSI-SuE1: Plenary Session

The ability to control individual quantum systems - spins, photons, and solids - has enabled new approaches to computing, communication, and sensing. Extending this control from individual qubits to quantum matter calls for engineering both the microscopic constituents of a material and the electromagnetic fields through which they interact. In this talk, I will describe our efforts to develop quantum systems from the bottom up, beginning with long-coherence rare-earth qubit and quantum memories and progressing toward photonic control of nonequilibrium electronic states. The connecting theme is the co-design of materials and their optical environment, using thin-film growth and device integration to create quantum functionality.

Our approach begins with bottom-up rare-earth quantum materials grown by molecular-beam epitaxy. Telecom-wavelength erbium spin-photon interfaces combine long optical and spin coherence with compatibility with photonic and superconducting circuits, linking localized quantum degrees of freedom to photons that can propagate through optical fiber. I will discuss how epitaxial materials development and heterogeneous integration together provide a foundation for entangling spins to photons and, ultimately, optically interconnected quantum nodes. Building outward from these interfaces, we have also demonstrated a direct telecom quantum link between integrated entanglement source and erbium solid-state quantum memory, exploiting their intrinsic spectral matching without quantum frequency conversion.

We extend this approach to quantum matter by growing an ultrathin Bi₂Se₃ topological-insulator film directly on an on-chip silicon photonic-crystal cavity. This integration combines epitaxial growth and optical confinement while preserving access to time- and angle-resolved photoemission spectroscopy. Under resonant ultrafast excitation, we directly observe cavity-driven Floquet-Bloch sidebands with delayed buildup and a response prolonged beyond the incident pulse. The cavity thus controls both the spatial confinement and temporal evolution of the drive, establishing a platform for using engineered photonic environments to manipulate nonequilibrium electronic states.

These efforts share a common strategy: engineer quantum functionality from the material upward, and use innovations in heterogeneous integration to bring distinct quantum degrees of freedom into controlled interaction. I will conclude with an outlook on how co-designing materials and photonic structures may expand this range toward hybrid quantum interconnects and new forms of hybrid quantum matter.