Physics & Astronomy News
"Understanding emergent collectivity and clustering in nuclei from a symmetry-based no-core shell-model perspective" by A. C. Dreyfuss, K. D. Launey, T. Dytrych, J. P. Draayer, R. B. Baker, C. M. Deibel, and C. Bahri.
We present a detailed discussion of the structure of the low-lying positive-parity energy spectrum of 12C from a no-core shell-model perspective. The approach utilizes a fraction of the usual shell-model space and extends its multishell reach via the symmetry-based no-core symplectic shell model (NCSpM) with a simple, physically informed effective interaction. We focus on the ground-state rotational band, the Hoyle state, and its 2+ and 4+ excitations, as well as the giant monopole 0+ resonance, which is a vibrational breathing mode of the ground state. This, in turn, allows us to address the open question about the structure of the Hoyle state and its rotational band. In particular, we find that the Hoyle state is best described through deformed prolate collective modes rather than vibrational modes, while we show that the higher lying giant monopole 0+ resonance resembles the oblate deformation of the 12C ground state. In addition, we identify the giant monopole 0+ and quadrupole 2+ resonances of selected light- and intermediate-mass nuclei, along with other observables of 12C, including matter rms radii, electric quadrupole moments, and E2 and E0 transition rates.
Student Spotlight - Allayjah Meredith
New Orleans native Allayjah Meredith, is a physics major with a concentration in astronomy at LSU.
"Electromagnetic duality anomaly in curved spacetimes" by I. Agullo, A. del Rio, and J. Navarro-Salas Published in Physical Review Letters 118 (2017) no.11, 111301
The source-free Maxwell action is invariant under electric-magnetic duality rotations in arbitrary spacetimes. This leads to a conserved classical Noether charge. We show that this conservation law is broken at the quantum level in presence of a background classical gravitational field with a non-trivial Chern-Pontryagin invariant, in a parallel way to the chiral anomaly for massless Dirac fermions. Among the physical consequences, the net polarization of the quantum electromagnetic field is not conserved.
Toward Predictive Theories of Nuclear Reactions Across the Isotopic Chart
Hosted at the Institute for Nuclear Theory at the University of Washington, Seattle, the INT Program INT-17-1a brought together physicists from the low-energy nuclear structure and reaction communities to identify avenues for achieving reliable and predictive descriptions of reactions involving nuclei across the isotopic chart. The 5-week program was organized by Jutta Escher (Lawrence Livermore National Lab), Charlotte Elster (Ohio University), Kristina Launey (LSU), and Dean Lee (North Carolina State University). In addition, a 1-week workshop, "Nuclear Reactions: A Symbiosis between Experiment, Theory and Applications" with co-organizers Jeff Blackmon (LSU) and Nick Scielzo (LLNL), was dedicated to the intersection of experiment, theory, and applications. The workshop focused on connecting theory developments to experimental advances and data needs for astrophysics and other applications.
Gabriela Gonzalez - Top 10 scientist of the year. A window opens to the universe
LSU Department of Physics & Astronomy Professor Gabriela González has played a central role in this groundbreaking discovery. She has served as the spokesperson for the large, international scienti c collaboration that detected gravitational waves called the LIGO Scienti c Collaboration, or LSC. She is also an experimental physicist whose research involves the reduction of noise to enhance the sensitivity of the gravitational wave detectors at the Laser Interferometer Gravitational-wave Observatories, or LIGO, as well as calibration of the detectors and analyzing the data.
“Entanglement dynamics of two nitrogen vacancy centers coupled by a nanomechanical resonator,” Z. Toklikishvili, L. Chotorlishvili, S. K. Mishra, M. Schueler, S. Stagraczynski, A. R. P. Rau, and J. Berakdar), J. Phys. B 50, 055007 (2017).
In this paper we study the time evolution of the entanglement between two remote NV Centers (nitrogen vacancy in diamond) connected by a dual-mode nanomechanical resonator with magnetic tips on both sides. Calculating the negativity as a measure for the entanglement, we find that the entanglement between two spins oscillates with time and can be manipulated by varying the parameters of the system. We observed the phe- nomenon of a sudden death and the periodic revivals of entanglement in time. For the study of quantum deco- herence, we implement a Lindblad master equation. In spite of its complexity, the model is analytically solvable under fairly reasonable assumptions, and shows that the decoherence influences the entanglement, the sudden death, and the revivals in time.
"Manipulation of entanglement sudden death in an all-optical setup" by A. Singh, S. Pradyumna, A. R. P. Rau, and U. Sinha, J. Opt. Soc. Am. B 34 (3), 681- 690 (2017)
The unavoidable and irreversible interaction between an entangled quantum system and its environment causes decoherence of the individual qubits as well as degradation of the entanglement between them. Entanglement sudden death (ESD) is the phenomenon wherein disentanglement happens in finite time even when individual qubits decohere only asymptotically in time due to noise. Prolonging the entanglement is essential for the practical realization of entanglement-based quantum information and computation protocols. For this purpose, the local NOT operation in the computational basis on one or both qubits has been proposed. Here, we formulate an all-optical experimental setup involving such NOT operations that can hasten, delay, or completely avert ESD, all depending on when it is applied during the process of decoherence. Analytical expressions for these are derived in terms of parameters of the initial state’s density matrix, whether for pure or mixed entangled states. After a discussion of the schematics of the experiment, the problem is theoretically analyzed, and simulation results of such manipulations of ESD are presented.
Researchers at LSU and Lund University discover new method of directing X-ray pulses
Researchers from LSU and Lund University in Sweden collaborated to find a new method for using strong laser pulses to direct short bursts of x-ray light. Department of Physics and Astronomy professor and lead researcher Kenneth Schafer, Department Physics and Astronomy professor Mette Gaarde and graduate student Seth Camp worked together to understand the theory behind this new method in directing and controlling x-ray light discovered by Lund University.
LSU partners with BREC for NanoDays event
The University partnered with BREC Parks for a kid-friendly NanoDays event March 25 at the Highland Road Park Observatory to teach the public basic science concepts. NanoDays is an annual “nationwide festival of programs about nanoscale science and engineering” and the potential future uses of nanotechnology, according to a news release from the LSU College of Science’s Department of Physics and Astronomy.
Jorge Pullin co-edited a book "Loop quantum gravity: the first 30 years"
Jorge Pullin has co-edited with Abhay Ashtekar, the Eberly Chair of Physics at the Pennsylvania State University, the volume "Loop quantum gravity: the first 30 years". It includes eight chapters by young emerging leaders of the field providing a snapshot of its state of the art, including one by LSU's Ivan Agullo and Parampreet Singh. The book is part of the series that World Scientific Publishing Co. of Singapore is putting out to celebrate the 100 years of Einstein's General Theory of Relativity. According to the publisher, It will include "two dozen excellent monographs written by top-notch authors from the international gravitational community".
"Surface phases of the transition-metal dichalcogenide IrTe2" by Chen Chen, Jisun Kim, Yifan Yang, Guixin Cao, Rongying Jin, E. W. Plummer
Transition-metal dichalcogenide IrTe2 has attracted attention because of striped lattice, charge ordering and superconductivity. We have investigated the surface structure of IrTe2, using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). A complex striped lattice modulations as a function of temperature is observed, which shows hysteresis between cooling and warming. While the bulk 5x1 and 8x1 phases appear at high temperatures, the surface ground state has the 6x1 phase, not seen in the bulk, and the surface transition temperatures are distinct from the bulk. The broken symmetry at the surface creates a quite different phase diagram, with the coexistence of several periodicities resembling devil's staircase behavior.
"Delicate competing electronic states in ultrathin manganite films" by Zhaoliang Liao, Rongying Jin, E. W. Plummer, and Jiandi Zhang
The coupling between the electrical transport properties of La2/3Sr1/3MnO3 (LSMO) thin films and structural phase transitions of SrTiO3 (STO) substrates at Ts=105K has been investigated. We found that the electrical resistivity of LSMO films exhibit a “cusp” at Ts, which is greatly amplified by tuning films to the verge of metallic and insulating phases, i.e., to the boundary of two delicate competing electronic states. Our results demonstrate that small amounts of strain can tip the subtle balance of competing interactions and tune the electronic properties in correlated electron materials.
"Uniqueness of the Fock quantization of scalar fields in a Bianchi I cosmology with unitary dynamics" by Jerónimo Cortez, Beatriz Elizaga Navascués, Mercedes Martín-Benito, Guillermo A. Mena Marugán, Javier Olmedo, José M. Velhinho
The Fock quantization of free scalar fields is subject to an infinite ambiguity when it comes to choosing a set of annihilation and creation operators, choice that is equivalent to the determination of a vacuum state. In highly symmetric situations, this ambiguity can be removed by asking vacuum invariance under the symmetries of the system. Similarly, in stationary backgrounds, one can demand time-translation invariance plus positivity of the energy. However, in more general situations, additional criteria are needed. For the case of free (test) fields minimally coupled to a homogeneous and isotropic cosmology, it has been proven that the ambiguity is resolved by introducing the criterion of unitary implementability of the quantum dynamics, as an endomorphism in Fock space. This condition determines a specific separation of the time dependence of the field, so that this splits into a very precise background dependence and a genuine quantum evolution. Furthermore, together with the condition of vacuum invariance under the spatial Killing symmetries, unitarity of the dynamics selects a unique Fock representation for the canonical commutation relations, up to unitary equivalence. In this work, we generalize these results to anisotropic spacetimes with shear, which are therefore not conformally symmetric, by considering the case of a free scalar field in a Bianchi I cosmology.
Controlling Fast X-ray Pulses with Laser Light
When hit by light, electrons are excited and begin to move. Ultrafast x-ray pulses may make it possible to watch the motion of these electrons as they move inside and between atoms in a material. Although scientists have gotten much better at making ultrafast x-rays in recent years, controlling them is still notoriously difficult. Researchers at LSU and Lund University in Sweden have demonstrated a new method to direct short bursts of x-ray light that uses strong laser pulses.
Small Science Wields Big Ideas LSU Celebrates NanoDays: The Biggest Event for the Tiniest of Science
Nanoscale structures, such as a single strand of DNA or gold nanoparticles in church windows, have existed in nature and been used long before scientists began devoting their studies to them. Recently, this innovative field of study has contributed to numerous discoveries such as advanced applications in energy, information storage and medicine. Because of its promising future, organizations across the country celebrate NanoDays, a nationwide festival of programs about nanoscale science and engineering. For the eighth consecutive year, LSU will host NanoDays at the Highland Road Park Observatory on Saturday, March 25, from 2-6 p.m.
Hall of Fame Astronaut Fred Gregory to Speak at LSU, Present Astronaut Scholarship Foundation Awards
Retired U.S. Air Force Col. and NASA astronaut Fred Gregory will visit LSU on Friday, March 17, at 11:30 a.m. at the Club at LSU Union Square to present two high achieving students with the Astronaut Scholarship Foundation scholarship and talk about his personal space exploration experience. The Astronaut Scholarship Foundation was created by the six surviving astronauts of Mercury 7 and aims to encourage students to pursue scientific endeavors that keep the U.S. on the leading edge of technology. LSU physics majors Harvey Shows and Amy LeBleu are among the top performing scholars to receive the ASF award. Col. Gregory is making a special visit to LSU to recognize their achievements. The event is co-sponsored by the Division of Student Affairs and College of Science.
"Using the Health Physics Student Volunteer Program for a Research Project Sponsored by the Medical Section of the Health Physics Society" by Joseph Steiner and Penny Leinwander
The Health Physics Society (HPS) Medical Health Physics Section (MHPS) received a request to research data on ra- diation safety guidance related to the death of patients who have recently received therapeutic doses of sealed or unsealed therapy sources. The MHPS elected to use student volunteers to perform this research. The purpose of this manuscript is to describe and provide a template for the process used by the MHPS to develop a student volunteer program. To implement the student volunteer program, the MHPS collaborated with the HPS Student Support Committee to develop a research proposal and a student volunteer selection process. The research proposal was sent to HPS student members in a call for volunteers. Two student volunteers were chosen based on predetermined qualifications to complete the work effort outlined in the research proposal. This project progressed with the use of milestones and culminated with the stu- dents presenting their findings at the annual HPS meeting. The students received HPS student travel awards to present at the con- ference. This work effort proved to be extremely beneficial to all parties involved.
"Callan-Giddings-Harvey-Strominger vacuum in loop quantum gravity and singularity resolution" by Alejandro Corichi, Javier Olmedo and Saeed Rastgoo
We study here a complete quantization of a Callan-Giddings-Harvey-Strominger (CGHS) vacuum model following loop quantum gravity techniques. Concretely, we adopt a formulation of the model in terms of a set of new variables that resemble the ones commonly employed in spherically symmetric loop quantum gravity. The classical theory consists of two pairs of canonical variables plus a scalar and diffeomorphism (first class) constraints. We consider a suitable redefinition of the Hamiltonian constraint such that the new constraint algebra (with structure constants) is well adapted to the Dirac quantization approach. For it, we adopt a polymeric representation for both the geometry and the dilaton field. On the one hand, we find a suitable invariant domain of the scalar constraint operator, and we construct explicitly its solution space. There, the eigenvalues of the dilaton and the metric operators cannot vanish locally, allowing us to conclude that singular geometries are ruled out in the quantum theory. On the other hand, the physical Hilbert space is constructed out of them, after group averaging the previous states with the diffeomorphism constraint. In turn, we identify the standard observable corresponding to the mass of the black hole at the boundary, in agreement with the classical theory. We also construct an additional observable on the bulk associated with the square of the dilaton field, with no direct classical analog.
Tabby Boyajian assesses competing ideas of star KIC 8462852
The strange behavior of Tabby’s Star, or KIC 8462852, has inspired modern astronomy’s wildest guessing game, with explanations ranging from aliens to sunspots. Writer Stephen Petranek got Tabby herself to assess the competing ideas.