Physics and Astronomy Colloquia

Department of Physics & Astronomy Colloquia

2017-2018 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$ü$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 T-symmetry is also violated. But to date no CP or T-symmetry violation has been observed in any strong force mediated process. This is known as the Strong-CP 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 Strong-CP problem and that neutral particles such as neutrons may spontaneously oscillate to their mirror universe counterpart ($n ↔ n*$) [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 in-turn 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$ü$ders, Det. Kong. Danske Videnskabernes Selskab, Mat.-fys. Medd., 28, No. 5 (1954).
[2] W. Pauli, Niels Bohr and the Development of Physics, McGraw-Hill, New York (1955): 30-51.
[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): 286-296.
[6] Z. Berezhiani and L. Bento, NeutronMirror-Neutron 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): 421-431.

•   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 non-physicists. The availability of near-ideal 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? D-Wave 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 D-Wave 2000Q with N>2000 qubits.

• Sept. 20, 2017* Dr. Mina Yoon, Oak Ridge National Laboratory jointly with University of Tennessee

• First-principles Materials by Design for Thermodynamically Stable Low-dimensional Electrides

Host: Dr. Seong-Gon Kim

Abstract:

Two-dimensional (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 low-dimensional 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 first-principles 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 first-principlescalculations-based 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$3O and $Ba$3N retain 1D anionic electrons along the hollow inter-rod sites; additionally, strong inter-rod interaction in $C$3O and $Ba$3N 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] First-Principles Prediction of Themodynamically Stable Two-Dimensional 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 one-dimensional building blocks, Changwon Park, Sung Wng Kim, Mina Yoon (2017, submitted to Phys. Rev. Lett.).

* Note the special colloqium date, Wednesday afternoon!

2017-2018 Committee

Lamiaa El Fassi (Chair) (325-0627, le334@msstate.edu email)
Benjamin Crider (325-4017, bpc135@msstate.edu email)
Ariunbold Gombojav (325-2927, ag2372@msstate.edu email)
Jinwu Ye (325-2926, jy306@msstate.edu email)
Secretary: Susan Galloway (325-2806, srg133@msstate.edu email)

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