Electromagnetically induced transparency in superconducting quantum circuits : Effects of decoherence, tunneling and multi-level cross-talk

TL;DR

This paper theoretically investigates electromagnetically-induced transparency (EIT) in superconducting quantum circuits, analyzing how decoherence, tunneling, and multi-level interactions affect EIT properties and potential decoherence diagnostics.

Contribution

The work extends previous EIT studies in superconducting circuits by analyzing imperfect dark-state preparation, decoherence effects, and off-resonant transitions, providing analytic expressions for population loss rates.

Findings

Rapid initial population loss due to imperfect dark state

Slower population loss influenced by detuning and decoherence

Analytic formulas linking decoherence mechanisms to population loss rates

Abstract

We explore theoretically electromagnetically-induced transparency (EIT) in a superconducting quantum circuit (SQC). The system is a persistent-current flux qubit biased in a $\Lambda$ configuration. Previously [Phys. Rev. Lett. 93, 087003 (2004)], we showed that an ideally-prepared EIT system provides a sensitive means to probe decoherence. Here, we extend this work by exploring the effects of imperfect dark-state preparation and specific decoherence mechanisms (population loss via tunneling, pure dephasing, and incoherent population exchange). We find an initial, rapid population loss from the $\Lambda$ system for an imperfectly prepared dark state. This is followed by a slower population loss due to both the detuning of the microwave fields from the EIT resonance and the existing decoherence mechanisms. We find analytic expressions for the slow loss rate, with coefficients that depend on the particular decoherence mechanisms, thereby providing a means to probe, identify, and quantify various sources of decoherence with EIT. We go beyond the rotating wave approximation to consider how strong microwave fields can induce additional off-resonant transitions in the SQC, and we show how these effects can be mitigated by compensation of the resulting AC Stark shifts.