  We study the diffusive behavior of chiral active (self-propelled) Brownian
particles in a two-dimensional microchannel with a Poiseuille flow. Using
numerical simulations, we show that the behavior of the transport coefficients
of particles, for example, the average velocity $v$ and the effective diffusion
coefficient $D_{eff}$, strongly depends on flow strength $u_0$, translational
diffusion constant $D_0$, rotational diffusion rate $D_\theta$, and chirality
of the active particles $\Omega$. It is demonstrated that the particles can
exhibit upstream drift, resulting in a negative $v$, for the optimal parameter
values of $u_0$, $D_\theta$, and $\Omega$. Interestingly, the direction of $v$
can be controlled by tuning these parameters. We observe that for some optimal
values of $u_0$ and $\Omega$, the chiral particles aggregate near a channel
wall, and the corresponding $D_{eff}$ is enhanced. However, for the nonchiral
particles ($\Omega = 0$), the $D_{eff}$ is suppressed by the presence of
Poiseuille flow. It is expected that these findings have a great potential for
developing microfluidic and lab-on-a-chip devices for separating the active
particles.
