Controlling and Protecting Quantum Information in Superconducting Oscillators

Modern quantum experiments allow the precise manipulation and measurement of many-body quantum states, promising to process quantum information to gain exponential advantages in computing, sensing, and communication. A hardware-efficient way to achieve such a processor is to manipulate quantum information stored in the continuous-variable (bosonic) phase space of electromagnetic radiation. Since photons in free space do not interact, such an approach necessarily requires the introduction of nonlinearity through strong light-matter couplings. However, since all matter is lossy, this inevitably introduces a trade-off between the speed of control and the inherited decoherence of the `light.' In this talk I will present my thesis work that introduces new techniques to control microwave radiation trapped in superconducting oscillators through interactions with Josephson junction-based nonlinearities. I first demonstrate novel methods for the programmable entanglement of two detuned oscillators through carefully constructed driven nonlinearities, achieving orders of magnitude higher fidelity than previously possible. This serves as the first demonstration of an erasure-limited controllable superconducting qubit. Using similar driven interactions, I then implement a bosonic control architecture and that is protected from any nonlinearity when idle, and implements clean multi-oscillator entangling gates when driven. Finally, I utilize such photon-exchanges to dynamically hybridize the bosonic mode and a transmon ancilla, in a way that regains universal control and measurement without inheriting the ancilla's decoherence. Together, this thesis provides a promising path toward error-resilient bosonic devices and bosonic error correction beyond the ancilla limit.