Alp Sipahigil (Advisor)

Ultralong lifetimes of silicon nanomechanical resonators at cryogenic temperatures and microwave frequencies make them promising resources in quantum engineering. In this work, we propose a nanomechanical qubit achieving strong single-phonon level anharmonicity of 5 MHz without the need for coupling to an ancillary qubit of a hybrid quantum architecture. This qubit design combines a nano-machined silicon cantilever brought in proximity to a silicon surface using microelectromechanical actuators. The surface forces between the cantilever and the silicon surface provide an effective...

Superconducting quantum circuits are leading candidates for quantum computing. Scaling up these systems for practical applications will require compact coherent qubits that store the quantum states, high fidelity quantum gates that process them, and a scalable architecture that can accommodate complex error correction circuits. Meeting such requirements is mainly impeded by the unavoidable presence of two-level systems (TLS), which act as a decoherence source that results in the loss of quantum information via phonon emission. In this project, we engineer superconducting circuits...

The overhead to construct a logical qubit from physical qubits rapidly increases with the de- coherence rate. Current superconducting qubits reduce dissipation due to two-level systems (TLSs) by using large device footprints. However, this approach provides partial protection, and results in a trade-off between qubit footprint and dissipation. This work introduces a new platform using phononics to engineer superconducting qubit-TLS interactions. We realize a superconducting qubit on a phononic bandgap metamaterial that suppresses TLS- mediated phonon emission. We use the qubit to probe its...