  The transition disk around the T Tauri star T Cha possesses a large gap,
making it a prime target for high-resolution imaging in the context of planet
formation. We aim to find signs of disk evolutionary processes by studying the
disk geometry and the dust grain properties at its surface, and to search for
companion candidates. We analyze a set of VLT/SPHERE data at near-infrared and
optical wavelengths. We performed polarimetric imaging of T Cha with IRDIS (1.6
$\mu$m) and ZIMPOL (0.5-0.9 $\mu$m), and obtained intensity images from IRDIS
dual-band imaging with simultaneous spectro-imaging with IFS (0.9-1.3 $\mu$m).
The disk around T Cha is detected in all observing modes and its outer disk is
resolved in scattered light with unprecedented angular resolution and
signal-to-noise. The images reveal a highly inclined disk with a noticeable
east-west brightness asymmetry. The significant amount of non-azimuthal
polarization signal in the $U_{\phi}$ images, with a $U_{\phi}$/$Q_{\phi}$
peak-to-peak value of 14%, is in accordance with theoretical studies on
multiple scattering. Our optimal axisymmetric radiative transfer model
considers two coplanar inner and outer disks, separated by a gap of 0.28"
(~30au) in size. We derive a disk inclination of ~69 deg and PA of ~114 deg. In
order to self-consistently reproduce the intensity and polarimetric images, the
dust grains, responsible for the scattered light, need to be dominated by sizes
of around ten microns. A point source is detected at an angular distance of
3.5" from the central star. It is, however, found not to be co-moving. We
confirm that the dominant source of emission is forward scattered light from
the near edge of the outer disk. Our point source analysis rules out the
presence of a companion heavier than ~8.5 $M_{\mathrm{jup}}$ between 0.1" and
0.3". The detection limit decreases to ~2 $M_{\mathrm{jup}}$ for 0.3" to 4.0".
