Quantum Control, Chaos, and Measurement with Superconducting Circuits

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NONTECHNICAL SUMMARYThis award supports theoretical research and education on the measurement and control of quantum mechanical systems that comprise circuits made from superconductors.Quantum physics has undergone a renaissance of activity, spurred on by the discovery of quantum information theory. The principles of quantum physics are being applied towards developing new kinds of computers, sensors, and simulators, that can surpass in performance their classical analogs. Superconducting quantum circuits are a leading candidate for making quantum computing elements because of fast processing speeds and their ability to preserve quantum information from environmental interference for long times. They are also excellent testbeds for fundamental quantum and condensed matter physics because they can be precisely controlled and measured. This PI and his group will advance theoretical investigations of these systems together with experimental collaborators. The research team will investigate the possibility of chaotic behavior emerging during the operation of these quantum systems. Chaos in this case is characterized by sensitive dependence of the system's dynamics to small changes to the system's initial conditions. Another problem that will be tackled is how to make measurements of system parameters as precisely as possible, a topic important for quantum sensing. A final research topic concerns how to transfer energy and light between spatially distant superconducting circuits. The educational component of the grant will provide training for graduate students, as well as a summer class for high-school students that will include teaching quantum physics at a qualitative level using minimal mathematics. In addition, the PI will write a book based on his previous experience teaching that class, presenting basic quantum phenomena at a high-school level. TECHNICAL SUMMARYThis award supports theoretical research and education to advance fundamental understanding of quantum control, chaos, and measurement with superconducting quantum circuits.At the interface of quantum and condensed matter physics there has been fruitful recent activity utilizing superconducting quantum circuits. This award funds several research topics in this frontier field. The PI and his research team will apply the stochastic path integral theory of continuous quantum measurements, developed in the PI's group, to research dynamical chaos of continuously measured, driven quantum systems. The most likely paths of the monitored quantum system are described by a set of nonlinear, deterministic, equations of motion. By considering a time-dependent Hamiltonian, chaos in the most likely paths is predicted to occur in relatively simple quantum situations. Quantum enhanced metrology for superconducting circuits will also be developed, building on recent demonstrations of a scaling-law improvement in the precision of frequency measurements. Limitations of decoherence for metrology may be overcome with methods such as dynamical decoupling. The PI's group will investigate more complicated cases where the parameter itself is a quantum one, so the measurement disturbance of the parameter must be considered. As a third topic, the research team will investigate energy and photon transfer with entanglement creation between superconducting cavities and circuits. The theoretical research will be pursued in collaboration with groups of experimental colleagues.The educational component of the grant will provide training for graduate students, as well as a summer class for high-school students that will include teaching quantum physics at a qualitative level using minimal mathematics. In addition, the PI will write a book based on his previous experience teaching that class, presenting basic quantum phenomena at a high-school level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.