Dr. Kemper received his PhD in Physics in 2010 from the University of Florida. He spent 2 years as a postdoctoral research at Stanford University and SLAC National Laboratory followed by serving as an Alvarez Fellow at Lawrence Berkeley National Laboratory before joining the faculty at NC State in 2015 as an assistant professor. He was promoted to associate professor in 2020.
During his PhD studies and continuing during his postdoctoral career, he used computational techniques to study the high-Tc cuprate superconductors, and the novel Fe-based superconductors that were discovered in 2006. Using a combination of Density Functional Theory, Quantum Cluster methods and computational modeling he addressed several aspects of the normal and superconducting states in these materials. Of particular note are a study of the gap symmetry in the Fe-based superconductors, as well as a joint experimental-theory paper showing the presence of four-fold symmetry breaking above the ordering temperatures in Co-doped BaFe2As2.
Starting during his postdoctoral career, and continuing now at NC State, he has embarked on a separate research project in non-equilibrium physics of complex materials. Non-equilibrium phenomena are studied experimentally using ultrafast lasers, which perturb the material under study and observing the subsequent dynamics. He has developed a set of software tools that theoretically model the pump-probe process in a variety of systems, which has to the first theoretical examinations of the pump-probe process. This has led to a series of works answering fundamental questions in non-equilibrium physics as well as collaborative works with experimentalists using pump-probe techniques to answer questions in materials physics.
In the past few years, Lex has started working in quantum computing and quantum information. His particular interest lie at the intersection of Quantum Computing and Condensed Matter Physics, where he is investigating how quantum computers can be used to solve problems in condensed matter.
Papers
Classification of dynamical Lie algebras for translation-invariant 2-local spin systems in one dimension
Classification of dynamical Lie algebras generated by spin interactions on undirected graphs
Denoising of Imaginary Time Response Functions with Hankel projections
A Unified Theory of Barren Plateaus for Deep Parametrized Quantum Circuits
Modulated time evolution for efficient variational ground-state preparation
Cheaper and more noise-resilient quantum state preparation using eigenvector continuation
Quantifying fault tolerant simulation of strongly correlated systems using the Fermi-Hubbard model
Geometric Quantum Machine Learning with Horizontal Quantum Gates
A linear response framework for simulating bosonic and fermionic correlation functions illustrated on quantum computers
Denoising and Extension of Response Functions in the Time Domain
Detection of a two-phonon mode in a cuprate superconductor via polarimetric RIXS
Robust measurements of n-point correlation functions of driven-dissipative quantum systems on a digital quantum computer
Quantum Eigenvector Continuation for Chemistry Applications
Evaluating robust entanglement on a trapped ion platform
Low-energy quasi-circular electron correlations with charge order wavelength in Bi2Sr2CaCu2O8+δ
Mapping the metal-insulator phase diagram by algebraically fast-forwarding dynamics on a cloud quantum computer
Robust measurement of wave function topology on NISQ quantum computers
Catalogue of phonon modes in several cuprate high-temperature superconductors from density functional theory
Algebraic Compression of Free Fermionic Quantum Circuits: Particle Creation, Arbitrary Lattices and Controlled Evolution
Measuring qubit stability in a gate-based NISQ hardware processor
Subspace Diagonalization on Quantum Computers using Eigenvector Continuation
An entanglement-based volumetric benchmark for near-term quantum hardware
Fixed Depth Hamiltonian Simulation via Cartan Decomposition
An Algebraic Quantum Circuit Compression Algorithm for Hamiltonian Simulation
Light-enhanced Charge Density Wave Coherence in a High-Temperature Superconductor
Determining ground-state phase diagrams on quantum computers via a generalized application of adiabatic state preparation
Algebraic Compression of Quantum Circuits for Hamiltonian Evolution
Quantum Markov Chain Monte Carlo with Digital Dissipative Dynamics on Quantum Computers
Quantum Fluctuations of Charge Order Induce Phonon Softening in a Superconducting Cuprate
Relaxation timescales and electron-phonon coupling in optically pumped YBa2Cu3O6+x revealed by time-resolved Raman scattering
Coherent control of asymmetric spintronic terahertz emission from two-dimensional hybrid metal halides
Simulating Quantum Materials with Digital Quantum Computers
Topological Quantum Computing on a Conventional Quantum Computer
Many Body Thermodynamics on Quantum Computers via Partition Function Zeros
Long-Time Error-Mitigating Simulation of Open Quantum Systems on Near Term Quantum Computers
What do the two times in two-time correlation functions mean for interpreting tr-ARPES?
Automated tracking of S. pombe spindle elongation dynamics
Timescales of excited state relaxation in α−RuCl3 observed by time-resolved two-photon photoemission spectroscopy
Probing the interplay between lattice dynamics and short-rangemagnetic correlations in CuGeO3 with femtosecond RIXS
Flatband-Induced Itinerant Ferromagnetism in RbCo2Se2
Fermi Liquid Theory Sheds Light on "Hot" EHL in 1L-MoS2
Nonequilibrium dynamics of spontaneous symmetry breaking into a hidden state of charge-density wave
Bridging the Gap Between the Transient and the Steady State of a Nonequilibrium Quantum System
Establishing non-thermal regimes in pump-probe electron-relaxation dynamics
Visualizing Tailored Spin Phenomena in a Reduced-Dimensional Topological Superlattice
Observing coherences with time-resolved photoemission
Quantum computation of magnon spectra
Driven-dissipative quantum mechanics on a lattice: Describing a fermionic reservoir with the master equation and simulating it on a quantum computer
Direct determination of mode-projected electron-phonon coupling in the time-domain
Higgs Oscillations in time-resolved Optical Conductivity
Theory of Time-Resolved Optical Conductivity of Superconductors: Comparing Two Methods for Its Evaluation
Band resolved imaging of photocurrent in a topological insulator
Coherent excitonic quantum beats in time-resolved photoemission measurements
Observation of chiral surface excitons in a topological insulator Bi2Se3
Detailed band structure of twinned and detwinned BaFe2As2 studied with angle-resolved photoemission spectroscopy
Identifying a forward scattering superconductor through pump-probe spectroscopy
Dense Electron–Hole Plasma Formation and Ultralong Charge Lifetime in Monolayer MoS2 via Material Tuning
Nonequilibrium Electron Dynamics In Pump-Probe Spectroscopy: Role Of Excited Phonon Populations
Interfacial Structure of SrZrxTi1−xO3 films on Ge
All-optical nonthermal pathway to stabilizing magnetic Weyl semimetals in pyrochlore iridates
General principles for the non-equilibrium relaxation of populations in quantum materials
Spectral Evidence for Emergent Order in Ba1-xNaxFe2As2
Ultrafast multi-terahertz probes of symmetry breaking in a stripe-phase correlated oxide
Photoemission signature of excitons
Nonequilibrium electron and lattice dynamics of strongly correlated Bi2Sr2CaCu2O8+δ single crystals
Dynamics of correlation-frozen antinodal quasiparticles in superconducting cuprates
Theoretical phase diagram for the room temperature Electron-Hole Liquid in photo-excited quasi-2D monolayer MoS2
Ultrafast Dynamics of Vibrational Symmetry Breaking in a Charge-ordered Nickelate
Amplitude mode oscillations in pump-probe photoemission spectra from a d-wave superconductor
Review of the theoretical description of time-resolved angle-resolved photoemission spectroscopy in electron-phonon mediated superconductors
Surface vibrational modes of the topological insulator Bi2Se3 observed by Raman spectroscopy
Relaxation of nonequilibrium populations after a pump, the breaking of Mathiessens rule
Creating stable Floquet-Weyl semimetals by laser-driving of 3D Dirac materials
Energy dissipation from a correlated material driven out of equilibrium
Spin-Polarized Surface Resonances Accompanying Topological Surface State Formation
Relationship between Population Dynamics and the Self-Energy in Driven Non-Equilibrium Systems
The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors
Theory of light-enhanced phonon-mediated superconductivity
Ultrafast lattice dynamics of the electronically driven, lattice directed charge density wave in TbTe3
Direct observation of Higgs mode oscillations in the pump-probe photoemission spectra of electron-phonon mediated superconductors
Bandwidth and Electron Correlation-Tuned Superconductivity in Rb0.8Fe2(Se1-zSz)2
Scattering bottleneck for spin dynamics in metallic helical antiferromagnetic dysprosium
Direct characterisation of photo-induced femtosecond lattice dynamics in BaFe2As2
Thickness-Dependent Coherent Phonon Frequency in Ultrathin FeSe/SrTiO3 Films
Classification of Collective Modes in a Charge Density Wave by Momentum-Dependent Modulation of the Electronic Band Structure
Theory of pump-probe photoemission in graphene; Ultrafast tuning of Floquet bands and local pseudospin textures
First-principles study of the phonon modes in bismuth-sillenites
Numerical integration for ab initio many-electron self energy calculations within the GW approximation
Balancing Act: Evidence for a Strong Subdominant d-Wave Pairing Channel in Ba0.6K0.4Fe2As2
Manipulation of gap nodes by uniaxial strain in iron-based superconductors
Distinguishing Bulk and Surface Electron-Phonon Coupling in a Photoexcited Topological Insulator
Exact solution for high harmonic generation and the response to an AC driving field for a charge density wave insulator
Effect of dynamical spectral weight distribution on effective interactions in time-resolved spectroscopy
Ultrafast electron dynamics in the topological insulator Bi2Se3 studied by time-resolved photoemission spectroscopy
Bandgap closure and reopening in CsAuI3 at high pressure
Dynamic competition between spin-density wave order and superconductivity in under doped Ba1-xKxFe2As2
Examining electron-boson coupling using time-resolved spectroscopy
Tunneling spectroscopy for probing orbital anisotropy in iron pnictides
Direct optical coupling to an unoccupied Dirac surface state in the topological insulator Bi2Se3
Time-dependent charge-order and spin-order recovery in striped systems
Electron-Mediated Relaxation Following Ultrafast Pumping of Strongly Correlated Materials; Model Evidence of a Correlation-Tuned Crossover between Thermal and Nonthermal States
Mapping of unoccupied states and relevant bosonic modes via the time dependent momentum distribution
Infrared study of the electronic structure of the metallic pyrochlore iridate Bi2Ir2O7
Structure and functionality of bromine doped graphite
Hot electron transport in a strongly correlated transition-metal oxide
Theoretical description of high-order harmonic generation in solids
Alternative route to charge density wave formation in multiband systems
Pulsed high harmonic generation of light due to pumped Bloch oscillations in noninteracting metals
Phase fluctuations and the absence of topological defects in a photo-excited charge-ordered nickelate
Density functional study of gold and iron clusters on perfect and defected graphene
Anisotropic quasiparticle lifetimes in Fe-based superconductors
Symmetry breaking orbital anisotropy on detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition
Theory of Two-Magnon Raman Scattering in Iron Pnictides and Chalcogenides
Sensitivity of the superconducting state and magnetic susceptibility to key aspects of electronic structure in ferropnictides
Spin fluctuations and superconductivity in a three-dimensional tight-binding model for BaFe2As2
Effects of cobalt doping and three-dimensionality in BaFe2As2
Curvature effect on the interaction between folded graphitic surface and silver clusters
Insensitivity of d-wave pairing to disorder in the high-temperature cuprate superconductors
Nonequilibrium Green's function study of Pd4-cluster-functionalized carbon nanotubes as hydrogen sensors
Projects
PauliTools - A collection of C++ tools to work with Pauli matrices in the binary symplectic representation.
cartan-quantum-synthesizer - Quantum Computing -- Unitary synthesis based on Cartan decomposition
EigenvectorContinuation -