  We show that an open quantum system in a non-Markovian environment can reach
steady states that it cannot reach in a Markovian environment. As these steady
states are unique for the non-Markovian regime, they could offer a simple way
of detecting non-Markovianity, as no information about the system's transient
dynamics is necessary. In particular, we study a driven two-level system (TLS)
in a semi-infinite waveguide. Once the waveguide has been traced out, the TLS
sees an environment with a distinct memory time. The memory time enters the
equations as a time delay that can be varied to compare a Markovian to a
non-Markovian environment. We find that some non-Markovian states show exotic
behaviors such as population inversion and steady-state coherence beyond
$1/\sqrt{8}$, neither of which is possible for a driven TLS in the Markovian
regime, where the time delay is neglected. Additionally, we show how the
coherence of quantum interference is affected by time delays in a driven system
by extracting the effective Purcell-modified decay rate of a TLS in front of a
mirror.
