
Department of Physics & Astronomy Colloquia
Hilbun 150, 125 Hilbun Hall, Mississippi State University
Mondays at 3:30 PM
20172018 Program
NB: Unless noted otherwise, Physics Colloquia are held as mentioned above.

 Oct. 23, 2017
Dr. Dipangkar Dutta, Mississippi State University
 Electrons with a twist: a new tool for nuclear physics
 Host: Dr. Lamiaa El Fassi
 Abstract:

The recent demonstration of electron beams carrying quantized orbital angular momentum (OAM), also known as twisted or vortex electron beams, provides a new and unexplored degree of freedom for use in nuclear and particle physics. For example, it could be used to probe fundamental questions about the origin of the proton's spin, such as, the contribution due to the orbital angular momentum of quarks and gluons in the proton. We will discuss how vortex electrons carry OAM and how they are generated, and possible scattering observables to monitor their twistedness? We will also discuss efforts underway at Jefferson Lab (JLab) to develop a new vortex electron sources in order to explore the use of Mott scattering to monitor its twistedness as well as verify the OAM preserving acceleration of the vortex electrons. If successful it could eventually lead to high energy electron beams carrying quantized OAM and open up a new frontier in nuclear physics.

 Oct. 30, 2017
Mr. Prajwal Mohanmurthy, Massachusetts Institute of Technology
 NStar: Searching for Mirror Neutron  Neutron Oscillations
 Host: Dr. Dipangkar Dutta
 Abstract:

The corner stone of standard model of particle physics is the Lorentz symmetry (a special result of which is Einstein's special theory of relativity). It was shown by G. L$\xfc$ders and Pauli that Lorentz symmetry translates to the join conservation of the three discrete symmetries of Charge inversion, Parity inversion and Time inversion [1, 2]. This equivalence is known as CPT theorem. Weak nuclear force mediated neutral Kaon (particle) decay (to 2 $\pi 0$ or to 3 $\pi 0$) showed that CP symmetry is violated [3]. Violation of CP symmetry is allowed by the CPT theorem, if Tsymmetry is also violated. But to date no CP or Tsymmetry violation has been observed in any strong force mediated process. This is known as the StrongCP problem [4]. It was pointed by Ref. [5] that introduction of a mirror realm (which does not interact with our real realm) could solve the StrongCP problem and that neutral particles such as neutrons may spontaneously oscillate to their mirror universe counterpart ($n\; \leftrightarrow \; n*$) [6]. Consequently, two separate groups performed their experiments in search
of such neutron  mirror neutron oscillations and reported having found no evidence of such oscillations [7, 8]. This inturn
set limits on the oscillation time, $\tau $_{nn*} > 414 s. Soon after, Ref. [9] pointed out inconsistencies in the results obtained by these two experiments. Furthermore, Ref. [9] showed that when the results of these two experiments are combined, the inconsistencies can be explained by introducing a mirror neutron oscillation in presence of a magnetic field in the mirror realm. Indeed, the two prior experiments had assumed the absence of any magnetic fields in the mirror realm and only considered applied real magnetic fields. Therefore we need a new experiment to verify or exclude these spurious results.
[1] G. L$\xfc$ders, Det. Kong. Danske Videnskabernes Selskab, Mat.fys. Medd., 28, No. 5 (1954).
[2] W. Pauli, Niels Bohr and the Development of Physics, McGrawHill, New York (1955): 3051.
[3] J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay, Phys. Rev. Lett. 13 (1964): 138.
[4] Mannel, Thomas, Theory and Phenomenology of CP Violation, Nuclear Physics B, 167 (2006): 170174.
[5] Z. Berezhiani, L. Gianfagna, M. Giannotti, Strong CP problem and mirror world: the Weinberg Wilczek axion revisited, Nuclear Physics B, Vol. 500, Issue 34, 22 (2001): 286296.
[6] Z. Berezhiani and L. Bento, NeutronMirrorNeutron Oscillations: How Fast Might They Be?, Phys. Rev. Lett. 96 (2006):081801.
[7] G. Ban et al., Phys. Rev. Lett. 99 (2007): 161603.
[8] A.P. Serebrov et al., Phys. Lett. B 663 (2008): 181.
[9] Z. Berezhiani, More about neutron  mirror neutron oscillation, Eur. Phys. J. C 64 (2009): 421431.

 Nov. 6, 2017
Dr. Mark Novotny, Mississippi State University
 Quantum Supremacy in 2018? Adiabatic Quantum Computers: Huge Advance or All Hype?
 Host: Dr. Benjamin Crider
 Abstract:

This colloquium is suitable for nonphysicists. The availability of nearideal quantum annealing machines, also known as Adiabatic Quantum Computers (AQC), with about N>50 qubits would be an extremely disruptive technology (see attached picture). A qubit is a quantum superposition of the 0 and the 1 bit at the heart of all binary technology. The ability of an ideal AQC to perform calculations impractical for any binary computer is why governments and companies (including Google) are making substantial investments in AQC. Google has as a stated goal to achieve quantum supremacy in 2018   what will that mean? DWave produces a quantum annealing machine with N>2000 qubits. An introduction to AQC machines will be presented. Questions addressed will include whether current AQC technologies: are adiabatic? are quantum? are a computer? If AQC are not all hype, it is an impactful new tool. As with any new tool three things should be done: 1) test the current tool, 2) understand applications enabled by the availability of the current tool and future advanced tools, 3) work to improve next generations of the tool. All three will be touched on in this lecture, including tests and applications of the DWave 2000Q with N>2000 qubits.

 Sept. 20, 2017*
Dr. Mina Yoon, Oak Ridge National Laboratory jointly with University of Tennessee
 Firstprinciples Materials by Design for Thermodynamically Stable Lowdimensional
Electrides
 Host: Dr. SeongGon Kim
 Abstract:

Twodimensional (2D) electrides, emerging as a new type of layered material whose electrons are confined in interlayer spaces instead of at atomic proximities, are receiving interest for their high performance in various (opto)electronics and catalytic applications. A realization of electrides
containing anionic electrons has been a great challenge because of their thermodynamic stability. For example, experimentally, only a couple of layered nitrides and carbides have been identified as 2D electrides. We developed a materials by design scheme and applied it to the computational exploration of new lowdimensional electrides. Our approach here offers an important alternative that overcomes the current limitation on discovery of new 2D inorganic electrides. By combining the global structure optimization method and firstprinciples calculations, we identified new thermodynamically stable electrides that are experimentally accessible. Most remarkably, we, for the first time, reveal an effective design rule for 2D electrides [1]. We then discover another new class of electrides based on 1D building blocks by coupling materials database searches and firstprinciplescalculationsbased analysis. This new class of electrides, composed of 1D nanorod building blocks, has crystal structures that mimic $\beta TiCl$_{3} with the position of anions and cations exchanged. Unlike the weakly coupled nanorods of $\beta TiCl$_{3}, $Cs$_{3}O and $Ba$_{3}N retain 1D anionic electrons along the hollow interrod sites; additionally, strong interrod interaction in $C$_{3}O and $Ba$_{3}N induces band inversion in a 2D superatomic triangular lattice, resulting in Dirac nodal lines [2]. Our work [1, 2] represents an important scientific advancement over previous knowledge of realizing electrides in terms of both materials and design principles, and should interest the communities of catalytic chemistry, surface physics, and structural chemistry, as well as the related engineering disciplines.
[1] FirstPrinciples Prediction of Themodynamically Stable TwoDimensional Electrides, W. Ming, M. Yoon, M.H. Du, F. Liu, K. Lee, and S. W. Kim, J. Am. Chem. Soc. 138, 15336 (2016).
[2]. New electrides based on onedimensional building blocks, Changwon Park, Sung Wng Kim, Mina Yoon (2017, submitted to Phys. Rev. Lett.). * Note the special colloqium date, Wednesday afternoon!
Click here for 20162017 season
20172018 Committee
Lamiaa El Fassi (Chair) (3250627, le334@msstate.edu email)
Benjamin Crider (3254017, bpc135@msstate.edu email)
Ariunbold Gombojav (3252927, ag2372@msstate.edu email)
Jinwu Ye (3252926, jy306@msstate.edu email)
Secretary: Susan Galloway (3252806, srg133@msstate.edu email)
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