Title: Hybrid quantum phononics with superconducting qubits*

Abstract: Superconducting qubits, and the experimental architecture of circuit quantum
electrodynamics (cQED), have emerged as not only a promising platform for quantum
computation but also for investigating fundamental and applied aspects of
synthetic/hybrid quantum systems composed of qubits coupled to other quantum systems
or degrees of freedom. In particular, the ability to leverage the properties of
superconducting qubits to investigate and manipulate phononic degrees of freedom opens
the door to exploring new regimes of circuit quantum optics using high-frequency sound.
Due to the intrinsically strong nonlinearity provided by the qubit, these types of hybrid
“quantum acoustic” systems have the potential to access a broad class of quantum states
of motion beyond what is achievable with effectively linear optomechanical or
electromechanical interactions.
In this talk I will describe some of our recent experimental results investigating the
fundamental physics of hybrid systems based on superconducting qubits coupled to
piezoelectric surface and bulk acoustic wave devices and how these systems can be used
to develop next-generation technologies for quantum sensing, computation, and
communication. As I will describe, these engineered systems, in which quantum
information stored in the qubit can be controllably coupled to the microscopic surface
and bulk phonon modes of a piezoelectric crystal, are an ideal platform for investigating
the exotic behavior of synthetic open quantum systems and phononic interference in the
quantum regime. Additionally, I will describe how these devices pave the way to exciting
new technologies ranging from quantum-limited surface sensing to phonon-based
bosonic quantum memories.

*This work was supported by the National Science Foundation via Grant No. ECCS-2142846 (CAREER)

Speaker: Leonid Levitov (M.I.T)

Title: Spin chirality, quasiparticle dynamics and signatures of exotic superconductivity

Speaker: Cyprian Lewandowski, Florida State University

Speaker: Herbert Fertig. Indiana University

Title: A Tale of Two Bilayers

Abstract: Modern materials physics has made available true two-dimensional electron systems, in the form of atomic networks bonded only across a single plane.  These van der Waals systems may be formed from a variety of materials, with different electronic properties, which may be combined into bilayer heterostructures with properties not found in either layer individually.  In this talk we will describe quantum coherent states of two such systems, in which nesting plays an important role in determining the ground state phase diagram.  The first of these is a phosphorene – graphene bilayer, for which one finds Fermi surfaces with strong nesting overlaps, leading to spin-density wave ground states for sufficiently strong interactions.  The second involves an idealized bilayer in which each layer supports a particle-hole symmetric band structure, possibly with non-trivial topology.  For half-filling, we find that nesting of the Fermi surfaces on opposite layers leads to different exciton condensate states, separated by a first order transition line which ends in an unusual zero temperature critical endpoint.  We demonstrate that this endpoint is a signature of Lifshitz transitions hosted by the individual layers in the absence of interactions.   In this way their Fermi surface topologies leave an imprint in the interacting phase diagram, in regions where the states themselves are fully gapped and lack Fermi surfaces.

Speaker: Long Ju, MIT
Title: Emergent Quantum Phenomena in Crystalline Graphene

Abstract: Condensed matter physics has witnessed many emergent quantum phenomena driven by electron correlation and topology. Such phenomena have been mostly observed in conventional crystalline materials where flat electronic bands are available. In recent years, moiré superlattices built upon two-dimensional (2D) materials emerged as a new platform to engineer and study electron correlation and topology. In this talk, I will introduce a family of synthetic quantum materials, based on crystalline multilayer graphene, as a new platform to engineer and study emergent phenomena driven by many-body interactions. This system hosts flat-bands in highly ordered conventional crystalline materials and dresses them with proximity effects enabled by rich structures in 2D van der Waals heterostructures. As a result, a rich spectrum of emergent phenomena including correlated insulators, spin/valley-polarized metals, integer and fractional quantum anomalous Hall effects, as well as chiral superconductivities have been observed in our experiments. I will also discuss the implications of these observations for topological quantum computation.

Speaker:Dr.  Songyang Pu, University of Tennessee, Knoxville,

Title:  Imaging composite fermions with scanning tunneling microscopy

Abstract:  A composite fermion (CF) is a topological quasiparticle that emerges from a nonperturbative attachment of vortices to electrons in strongly correlated two-dimensional materials. Similar to noninteracting fermions that form Landau levels in a magnetic field, CFs can fill analogous “Lambda” levels, giving rise to the fractional quantum Hall (FQH) effect of electrons. Here, we show that Lambda levels can be directly visualized through the characteristic peak structure in the signal obtained via spectroscopy with scanning tunneling microscopy (STM) on a FQH state. Complementary to transport, which probes the low-energy properties of CFs, we show that high-energy features in STM spectra can be interpreted in terms of Lambda levels. We numerically demonstrate that STM spectra can be accurately modeled using Jain's CF theory. Our results show that STM provides a powerful tool for revealing the anatomy of FQH states and identifying physics beyond the noninteracting CF paradigm.

Brian Skinner

The Ohio State University

Department of Physics

Title:  Chiral Wigner Crystal Phases Induced by Berry Curvature

Abstract:  In 1934 Eugene Wigner first predicted that a gas of electrons is susceptible to a freezing transition when its density is low enough due to the long-range Coulomb interaction between electrons. This Wigner crystal (WC) state has only very recently been realized and visualized in two dimensional materials without applied magnetic field. Here I discuss new forms of the Wigner crystal state that can arise in materials with Berry curvature. I focus specifically on bilayer graphene, and discuss the phase diagram and the different ordered states of the Wigner crystal.

TBA