School of Physics Seminar - Professor Greg Fuchs

In this seminar I’ll discuss two recent experiments that explore new quantum platforms based on spins, magnons, and superconductors, each with eye toward future integration.  First, I’ll discuss recent experiments in which we hybridize superconducting resonator photons and magnons hosted by the organic ferrimagnet vanadium tetracyanoethylene (V[TCNE]_x) [1]. This work is motivated by the challenge of scalably integrating an arbitrarily-shaped, low-damping magnetic system with planar superconducting circuits, thus enabling a new class of quantum magnonic circuit designs.  We take advntage of the properties of V[TCNE]_x, which has ultra-low intrinsic damping, can be grown at low processing temperatures on arbitrary substrates, and can be patterned via electron beam lithography.  We demonstrate the scalable, lithographically integrated fabrication of hybrid quantum magnonic devices consisting of a thin-film superconducting resonator coupled to a low-damping, thin-film V[TCNE]_x microstructure.  Our devices operate in the strong coupling regime, with a cooperativity as high as 1181(44) at T~0.4 K, suitable for scalable quantum circuit integration. Then I’ll discuss our recent discovery of two new spin defects in GaN that each show optically detected magnetic resonance (ODMR) [2].  The search for new “quantum defects” has been motivated by the success of the diamond nitrogen-vacancy (NV) center as a platform for quantum sensing and networking, while realizing that NV centers have both strengths and shortcomings.  While diamond itself is an excellent material host for quantum defects, it is not a mature semiconductor platform and it lacks well-established doping and fabrication technologies.  Here we examine bright individual defect centers in GaN and find two distinct defect species in the red part of the visible spectrum.  In the first, we find a room temperature ODMR contrast of ~5% and identify that the associated S ≥ 1 resides in a metastable orbital state.  In the second, we find a large room temperature ODMR contrast of up to ~30% that is associated with an S ≥ 3/2 ground-state and excited state.  We characterize the defect symmetry axis and spin Hamiltonian of each defect, which provides clues as to the structure of these defects.  Although the nuclear spin bath provided by the GaN host leads to a larger spin transition linewidth than e.g. NV centers in diamond, the maturity of the host semiconductor and the brightness of the defects makes this system interesting for quantum sensors integrated with electronics in a mature semiconductor host.