## Research areas:

(** v)** Condensed matter physics

** (v)** Atomic, molecular and optical physics

** (v)** Materials science

**(v)** High Energy Physics

## Condensed matter physics

Condensed matter physics is a major fundamental branch of physics that studies the collective quantum dynamics of strongly interacting particles. Unlike high-energy physics, which focuses on elementary particles and forces as the fundamental building blocks of nature, condensed matter physics views the emergent phenomena arising from correlations and entanglement among many particles as the fundamental ones. Quantum field theory, on which both branches of physics rely, makes no distinction between these fundamental views. Examples of condensed matter researched at CQS are solid-state crystals, superfluids and superconductors, magnets, topological insulators, and ultra-cold gases of trapped atoms.

CQS theorists I.Satija, E.Zhao and P.Nikolic share a common interest in topological insulators. I.Satijahas been working on integer quantum Hall states in lattice potentials, with U(1) and SU(2) gauge symmetry groups, often placed in the context of ultra-cold atoms. Her collaborative work, which included the world-leading experimentalist Ian Spielman of NIST, E.Zhao, P.Nikolic and international collaborators, has resulted with the first proposals to experimentally measure Chern numbers in cold atom band-insulators, and create fermionic time-reversal-invariant topological insulators using cold atoms. She also explores novel topological quantum states that are possible only out of equilibrium, and has a long-term interest in the non-linear dynamics of solitons. E.Zhao’s research has scrutinized the transport and proximity-effect properties of interfaces between topological insulators and metals or superconductors, motivated in part by the quest for Majorana fermions. P.Nikolic has been interested in exotic strongly-correlated states of electrons in topological insulators, whose elementary particle constituents carry a quantized fraction of electron’s charge and spin.

Superconductivity is another area studied at CQS from multiple angles. E.Zhao is interested in non-equilibrium properties of superconductors, motivated by possible applications in electronic and spintronic devices, as well as quantum computers. P.Nikolic has been investigating the fundamental properties of superconductors with strong quantum fluctuations, motivated by the unending quest to understand the physics of cuprate high-temperature superconductors. His theory of vortex quantum dynamics and charge dynamics in cuprates, developed in collaboration with world-leading theorists Subir Sachdev (Harvard) and Zlatko Tesanovic (Johns Hopkins), has successfully addressed some of the key experimental observations in cuprates. P.Nikolic is also working on “topological” superconductors in large magnetic fields or topological insulators, where zero-point quantum fluctuations can melt a vortex lattice and produce “fractional” topological insulators, highly-entangled many-body quantum states amenable to quantum computation.

Other interests of the CQS theorists include the transport properties of mesoscopic to nano-scale quantum devices (E.Zhao), and exotic quantum states of localized magnetic moments found in frustrated quantum magnets (P.Nikolic).

A popular blog introduction about topological insulators and some key concepts in condensed matter physics can be found here.

## Atomic, molecular and optical physics

Atoms are the birthplace of quantum mechanics. The historic effort to understand atoms has grown over time into modern fields such as high-energy and condensed matter physics, which explore the constituents of atoms and complex systems made of many atoms respectively. Recently, however, the fundamental interest in atoms has been reinvigorated by the recent discoveries of experimental methods to manipulate the quantum behavior of many atoms, molecules and photons (particles of light). A new playground of quantum mechanics has been opened by this new ability to create idealized simulations of electronic solid-state materials or fundamental processes, and engineer novel quantum states of matter not possible in other systems.

Atomic physics research is done at CQS both theoretically and experimentally. All three CQS theorists,I.Satija, E.Zhao and P.Nikolic, are working on ultra-cold atomic or molecular gases. I.Satija has been interested in topological band-insulating states of cold atoms, as well as soliton dynamics and aspects of noise correlations in Bose-Einstein condensates. E.Zhao has been interested in exotic modulated superfluids, the orbital ordering patterns of atoms in higher bands of periodic potentials, dipolar Fermi gases, and topological phases of cold atoms. His recent collaboration with CQS postdocS.Bhongale has discovered that interacting fermions with dipole moments form solids with periodic modulations of bonds, rather than density. The research of P.Nikolic has mainly explored the unconventional many-body quantum states of fermionic cold atoms with nearly resonant scattering (unitarity). His work has characterized the universal dynamics of imbalanced fermion gases near unitarity, and extended its field-theoretical approach to fermionic atoms in lattice potentials and artificial gauge fields. This work lead to the theoretical discovery of novel pair-density wave supersolids, and the phase-diagram maps of vortex-FFLO and quantum vortex liquid states of atoms in artificially created gauge fields.

The CQS experimentalist K.Sauer is an expert on magnetic resonance phenomena. The research done in her Magnetic Resonance Laboratory (MRL) seeks to understand and exploit spin-dynamics in such systems as nuclear quadrupole resonance and optically pumped atoms. One of the goals of this research is to push the noise in such systems to their fundamental limit, to reveal the full capability of magnetic resonance at low-fields both as an analytic tool and for the detection of contraband substances.

The CQS experimentalist Mingzhen Tian is an expert on laser atomic spectroscopy, nonlinear and quantum optics, and quantum information. Her research is currently focused on rare-earth based solid state quantum memory and quantum computation, which are the important elements in developing quantum information science and technology. The research topics also include laser spectroscopic properties of rare-earth ions trapped in inorganic crystal lattice at cryogenic temperature, the coherent and incoherent processes under the excitation of composite laser pulses, and the influence of the static electric and magnetic fields. Study of these processes provides the information needed to set up the physical systems to demonstrate quantum memory and quantum computation and analyze and optimize the performance.

## Materials science

Materials science is an interdisciplinary field dealing with fundamental properties and characteristics of materials, and applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates elements of applied physics and chemistry. [Paraphrasing Wikipedia]

The CQS material scientist Y.Mishin is interested in the theory and atomistic modeling of materials, particularly materials interfaces, atomic diffusion, and mechanical behavior of metals and intermetallic compounds. Specific areas of interest include models of atomic interaction in materials, interfaces in materials (including grain and interphase boundaries, interfacial motion, segregation, chemical reactions and cohesion), atomistic theory and modeling of interfacial kinetics in materials, defects and diffusion in intermetallic compounds, and plastic deformation and fracture of metals and intermetallic compounds.