  Electromagnetically induced transparency and absorption (EIT and EIA) are
usually demonstrated by three-level atomic or atom-like systems. In contrast to
the usual case, we theoretically study the EIT and EIA in an equivalent
three-level system, which is constructed by dressing a superconducting
two-level system (qubit) dressed by a single-mode cavity field. In this
equivalent system, we find that both the EIT and the EIA can be tuned by
controlling the level-spacing of the superconducting qubit and hence
controlling the dressed system. This tunability is due to the dressed
relaxation and dephasing rates which vary parametrically with the level-spacing
of the original qubit and thus affect the transition properties of the dressed
qubit and the susceptibility. These dressed relaxation and dephasing rates
characterize the reaction of the dressed qubit to an incident probe field. We
also use recent experimental data on superconducting qubits (charge, phase, and
flux qubits) to demonstrate our approach and show the possibility of
experimentally realizing this proposal.
