Condensed Matter Physics Seminar

Microwave photons are an ideal system in which to study quantum optics as near field, resonant, and far field length scales are readily accessible.  I will describe two experiments in which we realize quantum and topological photonic circuits, respectively, as well as describe prospects for combining the two aspects.  Despite having 100,000 times less energy than visible photons, it has recently become possible to detect and create single microwave photons on demand, using them both for fundamental quantum optics experiments and as a vehicle to mediate quantum logic gates.  I will describe an experiment in which two superconducting qubits are coupled through multiple strongly coupled planar superconducting cavities --- a multi-pole cavity QED architecture, which can be thought of as a simple photonic material. A useful feature of this architecture for quantum computing is that dispersive interactions between qubits are suppressed exponentially in the number of cavities when detuned, while the resonant coupling remains very strong. I will discuss a gate protocol, the adiabatic multi-pole (AMP) gate, which uses the Stark shift of a single photon to produce high fidelity quantum logic gates.

Additionally, I will describe a microwave circuit which acts as a topological insulator (TI) for microwaves.  In this experiment, a synthetic gauge field is created by systematically varying the local couplings, leading to global topology in the band structure of the meta-material.  Because topology of this sort is a band-structure effect rather than a many-body effect it is possible to observe this phenomena robustly even at room temperature.  I will describe site-resolved measurements of the density of states of both the bulk and edge modes of the system, as well as time domain measurements directly showing the spin-orbit coupling of the edge modes.  The ability to easily make long range couplings also allow measurement in exotic global topologies such as a mobius strip.  Prospects towards realizations of such systems in the quantum regime with interactions will be discussed.