Engineering quantum electronic chips: realization and characterization of circuit quantum electrodynamics systems

Robert J. Schoelkopf

Paul Brookes, Giovanna Tancredi, Andrew D. Patterson +6 more

Critical slowing down of the time it takes a system to reach equilibrium is a key signature of bistability in dissipative first-order phase transitions. Understanding and characterizing this process can shed light on the underlying many-body dynamics that occur close to such a transition. Here, we explore the rich quantum activation dynamics and the appearance of critical slowing down in an engineered superconducting quantum circuit. Specifically, we investigate the intermediate bistable regime of the generalized Jaynes-Cummings Hamiltonian (GJC), realized by a circuit quantum electrodynamics (cQED) system consisting of a transmon qubit coupled to a microwave cavity. We find a previously unidentified regime of quantum activation in which the critical slowing down reaches saturation and, by comparing our experimental results with a range of models, we shed light on the fundamental role played by the qubit in this regime.

Y. N. Srivastava

Nicolas Dirnegger, Prineha Narang, Arpit Arora

Introducing new components and functionalities into quantum devices is critical in advancing state-of-the-art hardware. Here, we propose superconducting diodes (SDs) as a coherent nonreciprocal element in circuit quantum electrodynamics (cQED) architectures. In particular, we use an asymmetric SQUID as an SD controlled with a flux bias - nonreciprocal element with single control handle and on-chip modality. We spectroscopically characterize SD and show that flux bias acts cooperatively with the nonlinear diode response to induce direction-dependent resonance shifts in the transmission spectrum. We show that even with modest diode efficiency the isolation isolation ratio is sufficiently high, and scales with multiple SDs. We demonstrate the use of the SD as a coupler to realize coherent nonreciprocal qubit-qubit coupling. With a minimal two qubit system, we demonstrate nonreciprocal half-iSWAP, thereby showcasing the potential of intrinsic nonreciprocity as a tool to perform arbitrary two-qubit gates. Our work enables high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, where nonreciprocity is embedded at the device level.

Guillermo Romero, E. Solano, Lucas Lamata

C. M. Quintana

Abstract : Circuit Quantum Electrodynamics (cQED) is a highly promising platform for quantum control, quantum simulation, and quantum optics in a solid-state environment. Such systems consist of arti cial atoms coupled to superconducting resonators, and can be probed with microwave signals on a chip. This thesis theoretically and experimentally studies a method of quantum-limited Josephson parametric ampli cation for the improvement of such microwave measurements. A theoretical analysis of parametric ampli cation with a nonlinear quantum oscillator is given, along with an analysis of a particular implementation with a superconducting coplanar waveguide resonator shunted by an array of SQUIDs. A parametric ampli er chip is designed and a fabrication process is engineered. Measurements and analysis of a successfully fabricated device are presented, and future outlook is discussed.