Develops quantum metrology for ultra-weakly-coupled dark sectors and fundamental physics. Directions: (1) axion dark matter detection using entangled probe state preparation and superconducting qubit QND readout (HAYSTAC, ADMX); (2) dark radiation/energy detection with Cooper-pair box quasiparticle sensors; (3) GW detectors based on high-B-field microwave cavities probing early-universe phase transitions; (4) emergent gauge symmetries in quantum spin liquids. Co-PI DARPA QuSeN (quantum sensing of neutrinos, 2025). Devices/Sensors lead, DOE Quantum Science Center.

Develops superconducting qubits and QND microwave single-photon detectors, applying them both to scalable quantum computing architectures and to axion/dark-photon dark-matter search experiments as ultra-sensitive quantum sensors.

Pop's group builds superconducting quantum circuits from high-kinetic-inductance materials, above all granular aluminium, and uses them as detectors. The distinctive capability is single-microwave-photon detection and QND photon counting with superinductor-based devices -- an extremely low dark-count, quantum-limited receiver in the GHz band -- plus fluxonium-type qubits, quantum-limited and travelling-wave parametric amplification, and studies of quasiparticle and noise mechanisms that set coherence limits. The direct sensing payoff is dark-matter search: a photon counter that beats the standard quantum limit lets a haloscope integrate far faster than an amplifier-based readout. Relative to the established NV-ensemble quantum-sensing playbook (DEER, nanoscale NMR, T1 relaxometry at pT/sqrt(Hz) ensemble sensitivity), this is the microwave/superconducting counterpart to an NV ensemble -- same objective (detect an absurdly weak field), different physical platform and roughly opposite temperature regime. A recent addition to Stuttgart's 1st Institute of Physics, so the lab is being built out now, which usually means unusual latitude for a postdoc.