  The fundamental challenge underlying superconducting quantum computing is to
characterize heterogeneity and disorder in the underlying quantum circuits.
These nonuniform distributions often lead to local electric field
concentration, charge scattering, dissipation and ultimately decoherence. It is
particularly challenging to probe deep sub-wavelength electric field
distribution under electromagnetic wave coupling at individual nano-junctions
and correlate them with structural imperfections from interface and boundary,
ubiquitous in Josephson junctions (JJ) used in transmon qubits. A major
obstacle lies in the fact that conventional microscopy tools are incapable of
measuring simultaneous at nanometer and terahertz, "nano-THz" scales, which
often associate with frequency-dependent charge scattering in nano-junctions.
Here we directly visualize interface nano-dipole near-field distribution of
individual Al/AlO$_{x}$/Al junctions used in transmon qubits. Our THz nanoscope
images show a remarkable asymmetry across the junction in electromagnetic
wave-junction coupling response that manifests as "hot" vs "cold" cusp spatial
electrical field structures and correlates with defected boundaries from the
multi-angle deposition processes in JJ fabrication inside qubit devices. The
asymmetric nano-dipole electric field contrast also correlates with
distinguishing, "overshoot" frequency dependence that characterizes the charge
scattering and dissipation at nanoscale, hidden in responses from topographic,
structural imaging and spatially-averaged techniques. The real space mapping of
junction dipole fields and THz charge scattering can be extended to guide qubit
nano-fabrication for ultimately optimizing qubit coherence times.
