This work is a continuation of fundamental experiments in quantum optics using superconducting integrated circuits. Based on the paradigm of "circuit QED" developed by the PI's group, in which superconducting qubits are combined with microwave transmission line resonant cavities to realize the physics of the Jaynes-Cummings model with ultra-strong coupling, the team is pursuing the generation, manipulation, and measurement of non-classical states of the electromagnetic field. Using the tools developed for quantum information processing with superconducting devices, we have developed a new "two-cavity" circuit architecture during the current funding period. Here a single qubit, which provides nonlinearity, is combined with two microwave cavities, allowing new possibilities for nonlinear optics at the single quantum level. The main goal with this architecture was to develop a quantum non-demolition measurement capable of detecting single microwave photons. The team has experiments showing that they can indeed perform several repeated measurements on single photons. The main thrust of the continuation program will therefore be to characterize and understand this quantum measurement, and to observe single quantum jumps of the field in their solid-state system. This measurement capability can then be used to study the backaction of the measurement, observe the collapse of the cavity wavefunction, prepare nonclassical states by measurement post-selection, and investigate quantum control and feedback on few photon states.
The broader impacts of this work is that it will open a new area for fundamental studies of the quantum measurement of the electromagnetic field, as well as develop new technology for integrated circuits which operate at the single quantum level. The experiments that will be performed employ the novel features of the circuit QED system to observe and study phenomena that are mostly inaccessible with traditional AMO systems in quantum optics. The techniques and capabilities for single photon generation and detection could have major impact on the prospects for scalable quantum computation and communication in these superconducting circuits and also atomic/condensed matter hybrid systems such as ion and molecule chips. This project will also continue the trend established by earlier work to forge new connections between the atomic and condensed matter physics communities. This research will take advantage of the infrastructure and technical knowledge for fabrication and measurement of superconducting devices developed as part of the large, applied effort for development of quantum computing at Yale, but allows new and distinct directions of fundamental physical interest.
Intellectual merit: This work of our program on fundamental experiments in quantum optics using superconducting integrated circuits. Based on the paradigm of "circuit QED" developed by the PI’s group, in which superconducting qubits are combined with microwave resonant cavities to realize the physics of the Jaynes-Cummings model with ultra-strong coupling, we are pursuing the generation, manipulation, and measurement of non-classical states of the electromagnetic field. Using the tools developed for quantum information processing with superconducting devices, we have realized a new 3D version of a "two-cavity" circuit architecture with significantly extended coherence times during the current funding period. Here a single qubit, which provides nonlinearity, is combined with two microwave cavities, allowing new possibilities for nonlinear optics at the single quantum level. We used these devices to observe new quantum phenomena, such as the single-photon Kerr regime, and to manipulate states of microwave fields in new ways. We demonstrated the ability to create interesting non-classical states, including the largest "Schrodinger cat states" (superpositions of Glauber coherent states) ever produced, and measured them with full Wigner state tomography. This work opens new possibilities for employing cavities and the physics of continuous variables in quantum information processing. Our main goal with this architecture is to develop real-time quantum non-demolition measurements capable of detecting single quantum jumps, and utilize this to actively stabilize states and perform quantum error correction. The physics and capabilities developed here can have significant impact on the prospects for scalable quantum information processing with solid-state devices. Broader impacts: The proposed work will open a new area for fundamental studies of the quantum measurement of the electromagnetic field, as well as develop new technology for integrated circuits which operate at the single quantum level. The proposed experiments employ the novel features of the circuit QED system to observe and study phenomena which are mostly inaccessible with traditional AMO systems in quantum optics. The techniques and capabilities for single photon generation and detection could have major impact on the prospects for scalable quantum computation and communication in these superconducting circuits and also atomic/condensed matter hybrid systems such as ion and molecule chips. This project will also continue the trend established by earlier work to forge new connections between atomic and condensed matter physics communities. Funds from this proposal were primarily used for a graduate student support. Results was disseminated via publications and presentations at conferences in the areas of AMO physics, quantum information, and condensed matter physics, as well as in tutorials and introductory lectures at summer schools and conferences. This research was leveraged off the infrastructure and technical knowledge for fabrication and measurement of superconducting devices developed as part of the large, applied effort for development of quantum computing at Yale, but allowed new and distinct directions of fundamental physical interest.
