We present an electro-absorptive THz antenna for the polarity-sensitive coherent sampling of THz lightwaves based on quantum dots. Introducing AC-bias, we effectively break the symmetry of the quantum-confined Stark effect in a layer of colloidal CdS-CdSe quantum dots. The alternating bias allows for the polarity-sensitive readout of THz-fields using differentially detected ultrafast electro-absorption. We investigate the underlying scaling behaviors, demonstrate first applications and discuss the prospects of THz-super-resolution imaging with Quantum-probe field microscopy (QFIM).