On-chip cavity studies of spin systems and nonlinear superconducting phenomena for quantum computing applications

Andrew Houck, Hakan E. Türeci, Jens Koch

In this dissertation, the use of on-chip superconducting (SC) resonators as a probe of spin-photon interactions as well as other superconducting phenomena will be presented. In particular, coherent Rabi oscillations are demonstrated for a spin s=1/2 ensemble in an ESR (Electron Spin Resonance) cavity as well as coherent multiphoton excitations. Applying techniques from the classical ESR measurements to an on-chip resonator is effectively shrinking the cavity volume and increasing vacuum field density. This in turn can greatly increase the sensitivity creating the possibility of probing the quantum to classical transition for spin-photon interactions. Additionally, an on-chip cavity provides the possibility of on-chip ESR measurements to be performed in a dilution refrigerator. Furthermore, progress has been made toward on-chip ESR type measurements. A highly sensitive heterodyne measurement setup has been developed, providing the capability of detecting signals as small as -125~dBm. Under the right conditions this setup may be able to detect single photons. To perform an on-chip ESR measurement, precise placement of the spin system at an anti-node of the magnetic field is required. For this, a technique for spin ensemble placement with micron scale precision is developed. Finally, performing ESR measurements requires the application of a (sometimes large) static field. Even a very small static field and can easily create vortices in a superconducting thin film when applied normal to the film plane. A precise alignment procedure is developed allowing for the operation of on-chip SC resonators to operate with an in-plane field up to 1~Tesla. This led to the first successful field-dependent observation of the nonlinear Meissner effect.

Seong Hyeon Park, Junyoung An, Jeseok Bang +1 more

Zhong-Peng Liu, Hui Wang, Jing Zhang +4 more

Quantum coherent feedback has been proven to be an efficient way to tune the dynamics of quantum optical systems and, recently, those of solid-state quantum circuits. Here, inspired by the recent progress of quantum feedback experiments, especially those in mesoscopic circuits, we prove that superconducting circuit QED systems, shunted with a coherent feedback loop, can change the dynamics of a superconducting transmission line resonator, i.e., a linear quantum cavity, and lead to strong on-chip nonlinear optical phenomena. We find that bistability can occur under the semiclassical approximation and photon antibunching can be shown in the quantum regime. Our study presents alternate perspectives for engineering nonlinear quantum dynamics on a chip.

James F. Annett, Balazs L. Gyorffy, Timothy P. Spiller

Andreas Angerer, Stefan Putz, Dmitry O. Krimer +9 more

Nonlinear systems, whose outputs are not directly proportional to their inputs, are well known to exhibit many interesting and important phenomena that have profoundly changed our technological landscape over the last 50 years. Recently, the ability to engineer quantum metamaterials through hybridization has allowed us to explore these nonlinear effects in systems with no natural analog. We investigate amplitude bistability, which is one of the most fundamental nonlinear phenomena, in a hybrid system composed of a superconducting resonator inductively coupled to an ensemble of nitrogen-vacancy centers. One of the exciting properties of this spin system is its long spin lifetime, which is many orders of magnitude longer than other relevant time scales of the hybrid system. This allows us to dynamically explore this nonlinear regime of cavity quantum electrodynamics and demonstrate a critical slowing down of the cavity population on the order of several tens of thousands of seconds-a time scale much longer than observed so far for this effect. Our results provide a foundation for future quantum technologies based on nonlinear phenomena.