Quantum Microwave to Optical Transduction with Light-Robust Superconducting Circuits

Citation

Wood, Steven (2024) Quantum Microwave to Optical Transduction with Light-Robust Superconducting Circuits. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kkbj-ex94. https://resolver.caltech.edu/CaltechTHESIS:03222024-181941076

Abstract

Modern computing and communication technologies such as supercomputers and the internet are based on optically connected networks of microwave frequency information processors. In recent years, an analogous architecture has emerged for quantum networks with optically distributed entanglement between remote superconducting quantum processors, a leading platform for quantum computing. The high coherence, controllability and scalability of microwave frequency superconducting circuits are ideal test-beds for nodes of a quantum network, however, microwave photons are not well suited for transmission of quantum information over long distances due to the presence of a large thermal background at room temperature. Optical photons are ideal for quantum communication applications due to their low propagation loss and negligible thermal occupation at room temperature. Coherent transduction of single photons from the microwave to the optical domain has the potential to play a key role in quantum networking and distributed quantum computing. In this thesis, we present the design of a piezo-optomechanical quantum transducer where transduction is mediated by a strongly hybridized acoustic mode of a piezoacoustic cavity attached to an optomechanical crystal. Our design involves on-chip integration of a light-robust superconducting circuit with the piezo-optomechanical transducer. Absorption of stray photons from the optical pump used in the transduction process is known to cause excess decoherence and noise in the superconducting circuit. The recovery time of the superconducting circuit after the optical pulse sets a limit on the transducer repetition rate. We fabricate niobium nitride based superconducting circuits and test their response to illumination by a 1550nm laser. We find a bandwidth-limited recovery time of $\sim$ 1us, indicating that a repetition rate exceeding 10kHz should be possible. Combined with the expected efficiency and noise metrics of our design, we expect that a transducer in this parameter regime would be suitable to realize probabilistic schemes for remote entanglement of superconducting quantum processors. We show non-classical microwave-optical photon correlations of the niobium nitride aluminum nitride transducer operated as a spontaneous parametric down conversion source. We go on to show the preparation and characterization of microwave-optical Bell states prepared by the transducer. And finally, we conclude by discussing the challenges with fabricating niobium nitride superconducting circuits and lithium niobate piezoacoustic devices on silicon-on-insulator substrates and provide steps towards realizing our enhanced transducer design.

Thesis Files