Caltech Young Investigators Lecture

Abstract: Superconducting circuits have emerged as one of the leading platforms for realizing a universal quantum computer. They are relatively easy to design, simulate, and fabricate, and their coherence times have improved enormously over the past decade. However, to date there still does not exist a clear technology roadmap for building a fault-tolerant computer due to several challenges. An error-corrected processor with even a relatively small number of logical qubits (~100) will require orders of magnitude many more physical qubits than anything demonstrated to date. So a first challenge is that, because resonant electromagnetic circuits operating at microwave frequencies have large footprints, the space available to fabricate them on a chip is severely limited. In addition each qubit generally requires several lines for readout and control, so wiring a chip at the bottom of a dilution refrigerator quickly becomes intractable.

Here I propose to alleviate these challenges by integrating superconducting qubits with nanomechanical resonators, using the latter as ultracompact quantum memories. I will first present an architecture in which a single superconducting qubit coupled to several resonators can be used to sequentially perform one and two qubit gates between any pair of them, turning the original qubit into a ‘module' with a much larger Hilbert space. I will then present the first experimental demonstration of direct, resonant coupling between a superconducting circuit and a phononic crystal defect cavity (PCDC), a nanostructure which localizes sound waves at a single defect site in an artificial lattice. I will also show new results demonstrating strong coupling of a transmon qubit to an array of PCDCs with localized resonances in the gigahertz range. I will conclude with a discussion on how this platform additionally enables new demonstrations in quantum acoustics such as non-demolition detection of single phonons and generation of Schrödinger cat states.

Bio: Patricio ArrangoizArriola is a PhD candidate in Applied Physics at Stanford University, working in the group of Amir SafaviNaeini. He received a Bachelor's in Physics from Caltech in 2014, where he worked under the supervision of Paul Bellan and Axel Scherer. His doctoral research is on developing hybrid approaches to scaling up superconducting quantum computing technologies. As part of these efforts he worked on techniques to model and simulate the interaction of superconducting qubits and piezoelectric nanostructures and developed a set of fabrication processes to integrate these two technologies on a single chip. His work with lithium niobate has enabled the creation of new nanoscale devices that were previously inaccessible with this material, including phononic and optomechanical crystals directly wired to superconducting circuits. He also contributes to a number of other efforts in the group, including microwave-to-optical conversion of single photons with lithium niobate modulators and various experiments in circuit quantum electrodynamics.

This lecture is part of the Young Investigators Lecture Series sponsored by the Caltech Division of Engineering & Applied Science.