Scanning SQUID Microscopy on fractional flux quanta with on-chip field control

Scanning Superconducting Quantum Interference Device (SQUID) Microscopy (SSM) is a scanning probe technique that utilizes the high magnetic field sensitivity of a SQUID to image local magnetic field of a sample surface. SSM played a vital role in showing the d-wave symmetry in cuprate superconductors by measuring fractional flux quanta, created spontaneously due to the cuprate acting as a π-shift element.

Now we continue on this by incorporating an on-chip bias line that can produce a local magnetic field. This allows us to control the flux state of nearby Nb-YBCO hybrid loops that exhibit fractional flux behavior. We have demonstrated the ability to freely change between the +1/2 Φ₀ and -1/2 Φ₀ states. Additionally, we study transitions into higher flux states (±3/2 Φ₀, ±5/2 Φ₀). These results are a crucial step to using controllable superconducting loops with π-shift elements in quantum annealing computing.