A new quantum simulator uses microwave photons in a superconducting cavity to simulate particles on a lattice similar to those found in superconductors or atomic nuclei.
The recent rapid advancement in the ability to create and manipulate superconducting qubit systems has created an exciting opportunity to construct quantum materials from the ground up, artificial atom by atom. This thesis will explore the creation of a new architecture of quantum simulation in which we use the circuit quantum electrodynamics toolbox to build quantum topological materials that so far have proven difficult to understand with theory, simulate with computational methods, and realize/measure with other quantum systems. Specifically we design a two-dimensional material in which microwave photons living in a superconducting 3D microwave cavity lattice interact strongly with a time-reversal symmetry breaking magnetic field and with each other. This is the first photonic topological lattice platform compatible with strong interactions. The combination of these interactions will enable the study of fractional quantum Hall systems, where fractionally charged particles called anyons are theorized to exist. This thesis describes how to engineer a tunable, low loss microwave lattice, create a magnetic field for chargeless photons using ferrite crystals, and generate inter-particle interactions using Josephson junction transmon qubits.
Summary form only given. A microscopic system under continuous observation exhibits at random times sudden jumps between its states. Quantum jumps of trapped massive particles (electrons, ions or molecules) have already been observed, which is not the case of the jumps of light quanta. Here we report on the first observation of photon number quantum jumps. Microwave photons are stored in a superconducting cavity for times in the second range. They are repeatedly probed by a stream of non-absorbing atoms. An atom interferometer measures the atomic dipole phase shift induced by the non-resonant cavity field, so that the final atom state reveals directly the presence of a single photon in the cavity. Sequences of hundreds of atoms highly correlated in the same state, are interrupted by sudden state-switchings. These telegraphic signals record, for the first time, the birth, life and death of individual photons. Applying a similar QND procedure to mesoscopic fields with tens of photons opens new perspectives for the exploration of the quantum to classical boundary.
Realizing and controlling the unconventional pairing featured by topological superconductors remains a central challenge. We introduce a cavity QED quantum simulator that engineers competing chiral px+ipy and dx2−y2+idxy orders by tailoring cavity-mediated couplings between atomic pseudospins that emulate momentum-dependent pairing channels. The desired spatially inhomogeneous cavity-mediated couplings can be engineered in a 2D optical lattice using incommensurate cavity-lattice wavelengths naturally occurring in cavity QED systems. This minimal and fully tunable platform enables controlled state preparation and continuous measurement of superconducting order parameters. To probe this competition, the platform enables selective excitation and direct time-domain detection of Bardasis-Schrieffer modes---collective excitations of the subdominant pairing channel. The same competing channel can have an even stronger impact out of equilibrium, where a sudden quench can drive its growth and abruptly reshape the dominant superconducting order, despite the stability of the dominant order in equilibrium. Together, these results establish cavity QED as a controlled setting for revealing hidden competing orders and exploring nonlinear dynamics of topological superconductivity that remain elusive in solid-state and ultracold-atom systems.