Condensed Matter Theory

Yale University, New Haven CT

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research in condensed matter physics of strongly correlated quantum systems and quantum optics. This project builds on theoretical progress during the previous grant period and is motivated by recent experimental advances in both two-dimensional electron gas transport measurements and quantum mechanics of electrical circuits known as "circuit QED." Motivated by recent surprising experiments on thermal transport in quantum Hall edge states, the PI will investigate why thermal excitations travel much shorter distances than charge excitations. The PI will examine sources of energy dissipation internal to soft edges as well as external sources associated with the intrinsic high-frequency dissipation in the bulk of the two-dimensional electron gas. Motivated by the remarkable recent experimental progress in "circuit QED", the PI will investigate the many-body physics of strongly interacting microwave polaritons in lattices of qubits and resonators. The PI aims to show how lattices of superconducting qubits and resonators can be used to simulate strongly correlated bosons as well as frustrated quantum spins. The PI will also continue research in collaboration with experimentalists on circuit QED both in terms of fundamental quantum optics and quantum computation, and on opto-nano-mechanics. This research includes investigations of the quantum and statistical mechanics of diverse important quantum phases of matter including such topics as: quantum coherence in mesoscopic electrical systems, opto-mechanical systems, novel correlated states of microwave photons, and two-dimensional electron gases. Applications and extensions of quantum optics ideas for superconducting circuits and opto-mechanical systems will continue to be developed. Analytical as well as quantum trajectory, classical Monte Carlo, and other numerical techniques will be applied to the study of these phenomena. New numerical techniques with wide applicability will be sought, developed and investigated. The proposed work will advance our knowledge on these broad fronts and will make close contact with experiment. NONTECHNICAL SUMMARY This award supports theoretical research and education on artificial atoms created from electrical circuits made from materials that are superconductors. Superconductors exhibit a quantum mechanical state which can conduct electricity without dissipation. Like real atoms, these artificial atoms can interact with a single quantum or photon of microwave radiation. These superconducting electrical circuits are being developed as the basic hardware for the construction of a quantum computer. A quantum computer would perform computations by manipulating quantum mechanical states and in principle can outperform the fastest existing computers for some problems. In addition to this potential practical application, these superconducting circuits can be used to study the fundamental quantum mechanics of many-particle systems interacting with electromagnetic fields. Normally electromagnetic waves pass through each other unaffected. In particle language, photons do not normally collide. However in the presence of artificial atoms, the photons effectively begin to interact and collide with each other. This can be used to study the quantum mechanics of many strongly colliding particles and to simulate phase transitions of solid materials using particles of light. The PI will propose experiments that can observe these new states of matter using light. The PI will also develop a theory of opto-mechanics in which the feeble pressure exerted by light can be used to cause mechanical motion of small objects and even cool their motion. Normally shining a laser on an object heats it up. However that it is possible to laser cool the motion of a material object just as the motion of individual atoms can be laser cooled. This is opening up a whole new technology with practical applications in optical communications and measurements.