Connecticut’s oldest planetarium will soon be back in action. Once used for education and outreach for UConn faculty, students, and community members, the planetarium fell into disuse in the last several years, but Department of Physics Assistant Professor-in-Residence Matt Guthrie has been working hard with skilled facilities staff, including CLAS Facilities Team Leader Brett DeMarchi, to bring this piece of UConn history back into working order.
UConn faculty and students will host a community event to view the solar eclipse at 2:00-4:30pm this Monday, April 8, on Horsebarn Hill (behind the Dairy Bar). Here in Storrs we’ll observe a maximum occultation of 92% at 3:28pm. This is a very exciting and special opportunity, since the next time that our location will […]
Two of UConn Physics Department’s undergrads, Rachel Cleveland and Nicholas Thiel-Hudson, have been recently selected as part of the 2024 cohort of UConn University Scholars! These students were selected based on the strength of their proposal. Graduation as a University Scholar recognizes a student’s extraordinary engagement with self-reflective learning and research or creative endeavors.
After years of disuse, the UConn Observatory, featuring a 16-inch optical telescope, is coming back into service. Physics faculty member Matt Guthrie, a driving force behind this rejuvenation effort spoke with UConn Today about the benefits offered by the Observatory both to students and to the community.
On October 14, 2023 40-50 members and friends of the UConn Physics department took part in the 51’st annual ascent up Mount Monadnock, near Jaffrey, New Hampshire. After the hike, the then-hungry hikers descended to the campground near Gilson Pond and enjoyed some well-earned refreshments.
Astrophysical observations give overwhelming evidence for the existence of dark matter. Several theoretical particles have been proposed as dark matter candidates, including weakly interacting massive particles (WIMPs), axions, and, more recently, their much lighter counterparts. However, there has yet to be a definitive detection of dark matter. For years, one group, the DAMA collaboration, has asserted that they observe a dark matter-induced annual modulation signal in their NaI(Tl)-based detectors. Their observations are inconsistent with those from other direct detection dark matter experiments under most assumptions of dark matter. In this talk, I will describe how I came to work on this topic and the debate’s current status, the worldwide experimental effort to test this extraordinary claim, and our progress toward resolving the current stalemate in the field.
Note: The pre-colloquium reception will be 3-4pm in the Gant Light Court
Graduate student Mitchell Bredice, Department of Physics, University of Connecticut
Kinetics, Nucleation, and Relaxation Dynamics of Ion-Seeded Nanoparticles
The recent interest in studying the adsorption and emission spectra of the hazy atmospheres of exoplanets stimulates the interest in clusters, small aggregates of atoms or molecules. The nucleation and dynamics of nanoparticles in the Earth’s atmosphere and their impact on the global climate and environment is another important area of research stimulating investigations of nucleation processes. However, how these small aggregates form is not wholly understood. Traditionally, nucleation of clusters or other phases is described through Classical Nucleation Theory. Although this theory has many discrepancies in describing the nucleation of submicron particles. In this work, we have performed molecular dynamics simulations of the nucleation of ion-seeded nanoparticles, specifically ArnH+ clusters, to investigate the microscopic mechanisms of nucleation from a gas or liquid phase. From these simulations, we have studied the stages of the nonequilibrium and equilibrium growth of ArnH+ clusters and analyzed the size distribution and internal energy relaxation of nascent clusters during different stages of their growth. The fundamental impact of the internal energy relaxation on the nonequilibrium nucleation of small ArnH+ clusters has been demonstrated. This analysis has generally been avoided in previous investigations due to assumptions of the equilibrium nature of the nucleation process. The results of our simulations showed that nanoparticles are formed in highly excited states, thus the cluster growth and relaxation are concurrent processes, and that relaxation of the cluster internal energy can delay cluster growth processes. To further investigate the internal energy relaxation, an ensemble of molecular dynamics simulations was performed for the detailed analysis of the average time evolution of kinetic, potential, and total energies of small ArnH+ clusters, and their kinetic energy relaxation. The results of the performed simulations have been explained through the use of a collisional Boltzmann equation describing the energy relaxation processes. Lastly, the general relationship between nonequilibrium growth and internal energy relaxation is discussed.
Dr. Esteban Goetz, Department of Physics, University of Connecticut
Interferometric Harmonic Spectroscopy for Electron Dynamics Imaging and Attosecond Pulse Train Phase Characterization
The advent of ultrashort light pulses has opened the possibility of investigating atomic and molecular processes on their natural time scales. In particular, Attosecond Transient Absorption Spectroscopy (ATAS) [1], a technique that allows to time-resolve the quantum dynamics of electrons by monitoring the absorption of extreme ultraviolet (XUV) radiation by an atomic or molecular system when the latter is dressed by an infrared (IR) laser source.
Motivated by recent experimental advances in self-referenced interferometric harmonic spectroscopy [2], we theoretically investigate an alternative approach to ATAS for electron dynamics imaging and attosecond pulse train (APT) phase characterization. In contrast to ATAS, which gives access to the imaginary part of the refractive index through an absorption measurement, an interferometric phase measurement gives information of its real part. In this talk, I will discuss the link between the XUV phase measurements of Ref. [2] and the different photoexcitation pathways occurring at the atomic level which are imprinted in the real part of the macroscopic refractive index. As an application, we show how such an interferometric approach can be used for phase retrieval of attosecond pulse trains based on two-arm harmonic spectroscopy and an optimization algorithm. Finally, I will highlight the impact of spin-orbit couplings and macroscopic and field propagation effects on the phase measurements and APT phase retrieval. Our theoretical description is based on numerical solution of the scalar Maxwell equations beyond Beer’s Law for the macroscopic field propagation coupled to the time-dependent Schroedinger equation for the quantum dynamics.
[1] M. Holler et al., Phys. Rev. Lett. 106, 123601 (2011)
[2] G. R. Harrison et al., arXiv:2305.17263 (2023)
Circuit complexity and functionality: a thermodynamic perspective
We explore a link between complexity and physics for circuits of given functionality. Taking advantage of the connection between circuit counting problems and the derivation of ensembles in statistical mechanics, we tie the entropy of circuits of a given functionality and fixed number of gates to circuit complexity. We use thermodynamic relations to connect the quantity analogous to the equilibrium temperature to the exponent describing the exponential growth of the number of distinct functionalities as a function of complexity. This connection is intimately related to the finite compressibility of typical circuits. Finally, we use the thermodynamic approach to formulate a framework for the obfuscation of programs of arbitrary length – an important problem in cryptography – as thermalization through recursive mixing of neighboring sections of a circuit, which can viewed as the mixing of two containers with “gases of gates”. This recursive process equilibrates the average complexity and leads to the saturation of the circuit entropy, while preserving functionality of the overall circuit. The thermodynamic arguments hinge on ergodicity in the space of circuits which we conjecture is limited to disconnected ergodic sectors due to fragmentation. The notion of fragmentation has important implications for the problem of circuit obfuscation as it implies that there are circuits with same size and functionality that cannot be connected via local moves. Furthermore, we argue that fragmentation is unavoidable unless the complexity classes NP and coNP coincide.
Quantum acoustics and the physics of the strange metals
ABSTRACT:
Quantum acoustics is the analog of quantum optics, with phonons playing the role of photons. The classical fields (electromagnetic, acoustic) are reached by virtue of coherent states in both cases. Quantum acoustics leads to two time dependent, interacting wave fields, one lattice, one quantum. The electron diffuses at a Planckian rate, independent of electron-lattice coupling and temperature, and the calculated resistivity is linear in temperature. Mott-Ioffe-Regel and Drude peak mysteries are also resolved. A rather different carrier transport scenario emerges for the strange metals.