Nonequilibrium phase transitions pose many questions and challenges, in part due to their complexity in theoretical descriptions, in part due to the experimental difficulties in systematically controlling systems out of equilibrium. In work now published in a new PRX article, the Houck Lab has studied a chain of 72 microwave cavities, each coupled to a […]
In a new preprint, we show how to implement a quantum optimal control algorithm with automatic differentiation executed on a GPU. This work, done in collaboration with the Schuster Lab, highlights how automatic differentiation allows one to specify advanced optimization criteria and incorporate them in the optimization process with ease. We demonstrate that the use […]
Photons are particles with rather special properties. They are easily created by a light source, absorbed by matter, and may repel or attract each other when in contact with a suitable material. The idea of feeding photons into crystal-like structures in which photons move between preferred positions and interact with each other, has recently captured […]
Andy Li presents his research during a poster session at the Northwestern site visit by the NSF MPS Directorate. (Photo credit: Roger Anderson)
The problem of interacting bosons in frustrated lattices is an intricate one due to the absence of a unique minimum in the single-particle dispersion where macroscopic number of bosons can condense. In this paper, we consider a family of tight-binding models with macroscopically degenerate lowest energy bands, separated from other bands by a gap.We predict […]
Microwave photons inside lattices of coupled resonators and superconducting qubits can exhibit surprising matter-like behavior. Realizing such open-system quantum simulators presents an experimental challenge and requires new tools and measurement techniques. Here, we introduce Scanning Defect Microscopy as one such tool and illustrate its use in mapping the normal-mode structure of microwave photons inside a […]
We study the properties of an advanced superconducting circuit, the 0-π circuit. This device, previously introduced by Brooks et al. in Phys. Rev. A 87, 052306 (2013), has multiple intriguing characteristics. With the right choice of parameters – it can exhibit a (near) degeneracy of the ground state, be robust with respect to dephasing, and […]
One of our group members, Andy (Cheong Yiu) Li, has received the 2014 World Quantitative and Science Scholarship by the WorldQuant Foundation. Find more information about the scholarship here.
The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad […]
Photon-based strongly-correlated lattice models like the Jaynes-Cummings and Rabi lattices differ from their more conventional relatives like the Bose-Hubbard model by the presence of an additional tunable parameter: the frequency detuning between the pseudo-spin degree of freedom and the harmonic mode frequency on each site. Whenever this detuning is large compared to relevant coupling strengths, […]