Prof. Francis RobicheauxI've been a
professor of physics at Purdue University since 2013 (previously at
Auburn University 19932013). My research area is Theoretical Atomic
Physics, focusing on coherence and decoherence in quantum
systems, many body processes when photons interact with many atoms,
highly
excited (Rydberg) atoms, strong fields, and
ultracold plasmas. My group typically consists of undergrads,
grad students, and postdocs. I'm a member of the ALPHA collaboration:
the first group to trap the antimatter version of the Hydrogen atom and
the only group to quantitatively measure its properties.


Graduate Student ResearchThere are funded positions available for graduate students. Interested graduate students should inquire about doing a 590 to try out research in the group.This page gives a brief description of the research done by Purdue graduate students. Different students have participated in projects supported by different grants with substantially different topics. However, the learning path of graduate students tends to be similar and most of the projects have a strongly numerical component. Typically, students start with a simplified project with many features of the research they will do. First, the students understand the basic idea behind their project. Then, they write their own computer programs to model the system they are studying. They learn to understand the limitations of their calculations and how to interpret their results. They numerically and theoretically explore the system under study. Finally, if the project successfully generates interesting data, they write the paper and make the figures for publishing their results. Once they have completed a project, they go to conferences or workshops to present the results in person which gives them practice in interacting with their peers. My goal for the students is that they become expert in an area of physics. In addition, I want them to gain mastery over all aspects of doing research. This is why they almost only use programs they have written themselves. Also, the students write their papers with editorial and organizational help from me. Ultimately, for most of their publications, the student is the first author reflecting that they are the major contributor to those results. The students are listed in reverse time order in the group. Deepak
Suresh (joined Jan 2020)
Deepak is supported by the NSF grant that focuses on the interaction of atoms with light with the goal of understanding how collective interactions lead to interesting coherent and decoherent phenomena. Deepak A. Suresh and F. Robicheaux, “Atom recoil in collectively interacting dipoles using quantized vibrational states,” Phys. Rev. A 105, 033706 (2022). PDF (378 kB) This is similar to Deepak's first paper but removes an approximation which seemed weak for the most interesting cases; after heroic calculations, he showed that the large atom recoils are possible when a photon interacts with many atoms. F. Robicheaux and Deepak A. Suresh, “Beyond lowest order meanfield theory for light interacting with atom arrays,” Phys. Rev. A 104, 023702 (2021). PDF (519 kB) (data for figures at https://doi.org/10.4231/YWCSA844) In this paper, we studied a method for systematically including higher levels of correlation in the modeling of many atoms collectively interacting with photons. Deepak A. Suresh and F. Robicheaux, “Photoninduced atom recoil in collectively interacting planar arrays,” Phys. Rev. A 103, 043722 (2021). PDF (655 kB) (data for figures at https://doi.org/10.4231/HHNZSP39) In this paper, we studied the recoil of atoms in arrays that result when photons interact with them and demonstrated cases of atom recoil hundreds of times larger than expected, effects important for quantum simulators and computers. Akilesh
Venkatesh (joined Jan 2019)
Akilesh is supported by the DOE grant that focuses on basic interactions of light, atoms, or electrons with single atoms. Akilesh Venkatesh and F. Robicheaux, “Interference in nonlinear Compton scattering using a Schrodingerequation approach,” Phys. Rev. A 103, 013111 (2021). PDF (456 kB) (data for figures at https://doi.org/10.4231/W4QYZB66) In this paper, we study the interference between Compton scattered photons at frequency 2f and nonlinear Compton scattered photons initially at frequency f. Akilesh Venkatesh and F. Robicheaux, “Effect of the orientation of Rydberg atoms on their collisional ionization cross section,” Phys. Rev. A 102, 032819 (2020). PDF (605 kB) In this paper, we classically calculated the interaction between a pair of highly excited atoms to understand details of ionization for this case. Akilesh Venkatesh and F. Robicheaux, “Simulation of nonlinear Compton scattering from bound electrons,” Phys. Rev. A 101, 013409 (2020). PDF (512 kB) In this paper, we tried to reproduce experimental results on nonlinear Compton scattering of intense Xrays from bound electrons using fully quantum methods. Troy
Seberson (joined Jan 2018, PhD Dec 2020)
Troy was supported by the ONR grant that focuses on the study of optically levitated nanoparticles. T. Seberson, Peng Ju, Jonghoon Ahn, Jaehoon Bang, Tongcang Li, and F. Robicheaux, “Simulation of sympathetic cooling an optically levitated magnetic nanoparticle via coupling to a cold atomic gas,” J. Opt. Soc. Am. B 37, 3714 (2020). PDF(811 kB) In this paper, we proposed a method for sympathetically cooling an optically levitated and magnetic nanoparticle using the magnetic moments of a nearby cold atomic gas. Jaehoon Bang, T. Seberson, Peng Ju, Jonghoon Ahn, Zhujing Xu, Xingyu Gao, F. Robicheaux, and Tongcang Li, “Fivedimensional cooling and nonlinear dynamics of an optically levitated nanodumbbell,” Phys. Rev. Research 2, 043054 (2020). PDF (1140 kB) In this experimental and theoretical paper, we modeled the behavior of optically levitated nanoparticles investigated experimentally by the Li group. T. Seberson and F. Robicheaux, “Stability and dynamics of optically levitated dielectric disks in a Gaussian standing wave beyond the harmonic approximation,” Phys. Rev. Research 2, 033437 (2020). PDF (795 kB) In this paper, we classically simulated the motion of optically levitated nanodisks and found an important nonlinear term in the motion. T. Seberson and F. Robicheaux, “Distribution of laser shotnoise energy delivered to a levitated nanoparticle,” Phys. Rev. A 102, 033505 (2020). PDF (953 kB) In this paper, we quantified the rate at which laser shotnoise affects different degrees of freedom of optically levitated nanoparticles. T. Seberson and F. Robicheaux, “Parametric feedback cooling of rigid body nanodumbbells in levitated optomechanics,” Phys. Rev. A 99, 013821 (2019). PDF (822 kB) In this paper, we classically simulated parametric feedback cooling of optically levitated symmetric top nanoparticles and showed correlation between different rotational motions the can prevent cooling in expermentally common arrangements. Xiao
Wang (joined Aug 2015, PhD Aug 2019)
Xiao was supported by the DOE grant that focuses on basic interactions of light, atoms, or electrons with single atoms. Xiao Wang and F. Robicheaux, “Ionization from Rydberg atoms and wave packets by scaled terahertz singlecycle pulses,” Phys. Rev. A 99, 033418 (2019). PDF(1130 kB) In this paper, we compared fully quantum calculations of ionization of a highly excited electronic state by a singlecycle pulse to those from classical calculations and explained the source of some differences. Xiao Wang and F. Robicheaux, “Angular interferences of sequentially ionized doublecontinuum wave packets,” Phys. Rev. A 98, 053407 (2018). PDF (1400 kB) In this paper, we used semiclassical ideas to explain interference patterns when two electrons are ejected from an atom using a time separated pair of laser pulses. Xiao Wang and F. Robicheaux, “Interference patterns from postcollision interaction in belowthreshold photoexcitation Auger processes,” Phys. Rev. A 98, 013421 (2018). PDF (1850 kB) In this paper, we used semiclassical ideas to explain interference patterns that arise when a single photon ejects two electrons from an atom. Xiao Wang and F. Robicheaux, “Probing double Rydberg wave packets in a helium atom with fast singlecycle pulses,” Phys. Rev. A 96, 043409 (2017). PDF (599 kB) In this paper, we described a method for probing a twoelectron quantum wave packet using a singlecycle electric field. A. P. Povilus, N. D. DeTal, L. T. Evans, N. Evetts, J. Fajans, W. N. Hardy, E. D. Hunter, I. Martens, F. Robicheaux, S. Shanman, C. So, X. Wang, and J. S. Wurtele, “Electron Plasmas Cooled by CyclotronCavity Resonance,” Phys. Rev. Lett. 117, 175001 (2016). PDF (1480 kB) In this experimental and theoretical paper, we provided the theoretical understanding of experimental results on the collective interaction of many electrons whose cyclotron frequency is resonant with a microwave cavity. X. Wang and F. Robicheaux, “Energy shift and state mixing of Rydberg atoms in ponderomotive optical traps,” J. Phys. B 49, 164005 (2016). PDF (934 kB) In this paper, we studied the trapping of Rydberg atoms by focussed light when the electronic state has a total angular momentum J > 0. Tyler
Sutherland (joined Aug 2014, PhD Dec 2017)
Tyler was supported by the NSF grant that focussed on the interaction of atoms with light with the goal of understanding how collective interactions lead to interesting coherent and decoherent phenomena. R.T. Sutherland and F. Robicheaux, “Degenerate Zeeman ground states in the single excitation regime,” Phys. Rev. A 96, 053840 (2017). PDF(363 kB) In this paper, we addressed the difficult problem where many atoms collectively interact through photons and have an exponentially large ground state manifold. R.T. Sutherland and F. Robicheaux, “Superradiance in inverted multilevel atomic clouds,” Phys. Rev. A 95, 033839 (2017). PDF (850 kB) Erratum In this paper, we addressed the difficult problem of understanding the collective decay of the excited state of many atoms when there are multiple final states the atoms can decay into. R.T. Sutherland and F. Robicheaux, “Collective dipoledipole interactions in an atomic array,” Phys. Rev. A 94, 013847 (2016). PDF (815 kB) In this paper, we studied the long range interaction between atoms in a linear array through photons and showed it can lead to qualitatively new and interesting behavior. R.T. Sutherland and F. Robicheaux, “Coherent forward broadening in cold atom clouds,” Phys. Rev. A 93, 023407 (2016). PDF (353 kB); Erratum In this paper, we studied how the long range interaction between atoms in a diffuse cloud through photons can lead to substantial decrease in the lifetime of excited states. Changchun
Zhong (joined Apr 2014, PhD Dec 2017)
Changchun was supported both by the DOE grant that focusses on basic interactions of light, atoms, or electrons with single atoms and the NSF grant that focussed on the understanding of coherence and decoherence in small quantum systems. Changchun Zhong, Tongcang Li, and F. Robicheaux, “Quantum calculation of feedback cooling a laser levitated nanoparticle in the shotnoisedominant regime,” arXiv:1708.01203 (2017). In this paper, we studied feedback cooling of levitated nonoparticles at the quantum level including the heating and decoherence from shotnoise of the levitating laser as well as using position or velocity data to feedback cool the nanoparticle. Changchun Zhong and F. Robicheaux, “Shotnoisedominant regime for ellipsoidal nanoparticles in a linearly polarized beam,” Phys. Rev. A 95, 053421 (2017). PDF(934 kB) In this paper, we studied the shot noise heating and feedback cooling of rotational motion of ellipsoidal nanoparticles at the classical level. Changchun Zhong and F. Robicheaux, “Decoherence of rotational degrees of freedom,” Phys. Rev. A 94, 052109 (2016). PDF (1220 kB) In this paper, we gave the first theoretical treatment of decoherence of rotational degrees of freedom of levitated nanoparticles due to their interaction with light. Changchun Zhong and F. Robicheaux, “Coherence and quasistable states in a strong infrared field,” Phys. Rev. A 93, 033410 (2016). PDF (646 kB) In this paper, we studied the quasistability of atoms in very strong infrared fields when the atoms were excited to near their threshold by a train of UV pulses. Changchun Zhong and F. Robicheaux, “Spectrum of quasistable states in a strong infrared field,” Phys. Rev. A 92, 013406 (2015). PDF (642 kB) In this paper, we studied the quasistability of atoms in strong infrared fields for binding energies where photon absorption should quickly lead to ionization. 
robichf[at]purdue.edu Links: 