This award supports research and education in theoretical condensed matter physics. Recent developments in the design of microwave circuits involving transistor-like elements made of superconductors have resulted in the ability to make electrical supercurrents interact strongly with microwaves. At sufficently low temperature, supercurrents in superconductors carry electricity without dissipation. The superconducting state involes the collective behavior of a large of electrons that together can exhibit properties of quantum mechanical states typical of the world of atoms and molecules even though the supercondutor itself is a macroscopic object. Preliminary work suggests that the resulting generated microwaves can be inherently low noise, somewhat akin to a laser. Such microwave sources may be useful for quantum communication purposes. The PI aims to develop a theoretical understanding of the nature of the microwaves that are generated as a result of these strong light-charge interactions. The PI will work in close collaboration with experimentalist. In a related thrust the PI will investigate a hybrid system where a superconducting transistor element couples microwaves with a nanoscale, mechanical vibrating wire. It is expected that this coupling will result in low inherent noise for the microwaves and coupled mechanical vibrations. This kind of vibrating nanowire device may enable the development of an ultasensitive force microscope. An overall goal of these two projects is to develop an understanding of how to generate steady-state, large amplitude microwave and nanomechanical motions that have manifestly quantum mechanical properties such as ultralow amplitude noise, otherwise known as "quantum squeezing."
A graduate student and advanced undergraduate students involved in the project will receive training in theoretical condensed matter physics. The students will benefit from having direct access to experimental results from colleague Prof. Rimberg's lab, and will help in the interpretation of the experiments.
This award supports theoretical research and education concerned with advancing understanding of a class of superconducting circuit systems that strongly couple microwave photons to Cooper pair transport and to nanomechanical motion. The activity comprises two superconducting circuit projects. One project will develop a comprehensive theory of the Cooper pair laser, in particular elucidating the quantum nature of the generated microwave cavity photons and modeling the data from recent and planned experiments. The other project will develop the theory for a related microwave cavity-Cooper pair circuit system that includes a nanomechanical resonator, also being realized in experiment. This recently proposed system achieves ultra strong coupling between the microwave cavity photons and nanomechanical energy quanta--phonons. The project will in particular address the generation of manifestly quantum states of the mechanical resonator involving large average phonon number. The theoretical investigation will complement a parallel experimental effort by Dartmouth colleague Prof. Alex Rimberg, also supported by the NSF. The goal of the project is to provide a better understanding of how to generate steady, quantum sources of microwaves and mechanical quantum states involving large average photon and phonon numbers. Robust, tunable sources of quantum microwaves may find application in quantum communication, while steady, continuously generated mechanical quantum states may find use in ultra sensitive position detection.
This award supports the training of a graduate student, as well as advanced undergraduate students involved in the research in theoretical condensed matter physics, gaining expertise in such areas as many body theory, mesoscopic quantum physics, nonlinear dynamics, quantum optics, and computational physics. The students will also have opportunities to apply their theoretical models to help explain experimental data from Prof. Rimberg's group.
