Andreev bound-state optoelectronics: Absorption spectroscopy and microwave-to-optical transduction

Superconducting weak-link junctions host electron-hole hybridized excitations called Andreev bound states, central to mesoscopic transport and emerging quantum information platforms. Andreev physics has so far been synonymous with the microwave range. However, advancements in superconductor-semiconductor hybrid junctions open the door to the characterization, and manipulation, of Andreev states by light. Here we introduce a model for light-Andreev interaction, with distinct features: Electrons transitioning into Andreev levels can sidestep Pauli exclusion, resulting in two optical absorption resonances separated by twice the bound-state energy. One resonance populates the Andreev state and the other empties it, enabling optical control of Andreev qubit parity; pumping both resets the junction and prevents saturation. Given their strong microwave coupling, we show how Andreev bound states can operate as optical-to-microwave transducers with MHz-scale intermode coupling, a key ingredient for heat load management and quantum networking. We illustrate these effects with realistic device parameters. Our results highlight the possibilities in the new field of Andreev optoelectronics.

We present a minimal model that couples Andreev bound states to optical-range light, forming the basis for Andreev optoelectronics. We identify the “anomalous” absorption of light by occupied ABSs. This counteracts junction saturation and allows continuous absorption of bichromatic light. Absorption can be measured by optical scattering or microwave response. Unlike tunneling spectroscopy, normal absorption and anomalous absorption are spectrally separated, enabling optical control of Andreev qubit parity. In addition, Andreev bound states mediate coherent transduction between optical and microwave photons, providing a direct route to optical readout and control of superconducting quantum circuits.

Ŀooking ahead, pulsed optical driving unlocks a myriad of time-resolved experiments and may permit the internal dynamics of the junction to be filmed. The ABSs also carry the Josephson current, begging the question of whether transport through the junction can be tuned with optical illumination as it can be with microwave irradiation [119,120]. Finally, beyond interfacing with microwave circuitry, the coupling we describe here may allow optical readout and control of quantum information stored directly in the Andreev levels.

Click here to read the entire article:  https://journals.aps.org/prb/abstract/10.1103/2fyj-67lt