On October 15, 2025, a seminar titled “The Role of LC Resonators in Superconducting Quantum Computing” was presented by Dr. Saleem Rao, Associate Professor, Physics Department.

Dr Rao opened with a concise introduction to quantum computing, covering what qubits are, how superposition and entanglement enable quantum advantage, the basics of gates and measurement (including Bloch sphere intuition), and why noise and error correction dominate system design. He briefly surveyed leading hardware platforms to frame where superconducting circuits fit in the landscape.

The session then traced two decades of progress across optical, trapped-ion, defect-center, and superconducting approaches, noting that fault tolerance remains elusive due to scalability and coherence limits. Focusing on planar cQED, Dr. Rao examined how LC resonators underpin the architecture: setting qubit and readout frequencies, engineering coupling rates, suppressing Purcell loss, and enabling multiplexed measurement. He emphasized how geometry and materials—lumped-element vs. coplanar designs, capacitor edge fields, and interface participation—govern internal quality factors and sensitivity to two-level system (TLS) defects at surfaces and interfaces.

Practical design considerations included materials and processing (Al/Ta films on sapphire or Si, surface treatments), dielectric-field management (trenching, substrate removal, vacuum gaps), and microwave packaging to reduce crosstalk. He highlighted emerging directions—high-kinetic-inductance superinductors, improved Purcell filters, and quantum-limited amplification—that incrementally extend coherence. Yet, Dr. Rao argued, a commercial-grade, fault-tolerant machine remains out of reach: TLS-limited variability, fabrication yield, cryogenic control scaling, and the steep overheads of error correction keep the bar high, even as LC resonators continue to be the quiet workhorses enabling next-generation superconducting devices.

The following are the highlights of the event: