Christina Bell An On-chip Millimeter-Wave Mach-Zehnder Interferometer for Quantum Sensing &Computing

We describe the development of superconducting circuit elements required for a millimeter-wave Mach-Zehnder (MZI) interferometer operating at 75-110 GHz (W-band). These element include a wide-band superconducting quadrature hybrid, a superconducting diplexer and current-controllable superconducting transmission line phase shifters in an inverted microstrip geometry. The superconducting transmission lines are fabricated from NbN and are coupled to W-band waveguides using radial probes. These circuit elements can be exploited as a platform to investigate millimeter wave circuit quantum electrodynamics such as the entanglement of millimeter-wave photons and applications in quantum sensing and quantum computing. Another application of a full MZI circuit is in astronomical and cosmological surveys as a Fourier transform spectrome ter.