-
Dissertation Defense, Niraj Ghimire- Density Matrix Renormalization Group studies of interacting dipoles in a zigzag chain- Ph. D. defense11:00am
6/26
Dissertation Defense, Niraj Ghimire- Density Matrix Renormalization Group studies of interacting dipoles in a zigzag chain- Ph. D. defense
Wednesday, June 26th, 2019
11:00 AM - 01:00 PM
Storrs Campus Gant West Room 103-A
Dissertation Defense
Niraj Ghimire
Physics Department
University of Connecticut
"Density Matrix Renormalization Group studies of interacting dipoles in a zigzag chain"
The goal of my research is to simulate quantum mechanics, which is known to be a very challenging problem even for the most advanced supercomputers of today. The system I have chosen consists of molecular dipoles in a quasi-one-dimensional optical lattice. For the first part of the talk, I will discuss the situation where the dipoles are polarized in the plane of the lattice at half-filling and double occupancy is not allowed on any lattice sites. The dipoles can hop around between sites and the interactions between them can be attractive or repulsive, with the hopping and interaction allowed up to second neighbors. I am particularly interested in the zero-temperature quantum phases induced by geometrical frustration, a situation where not all the interactions are satisfied. By mapping the dipoles in this lattice to a spin-1/2 model and by using the numerical approximation method known as density matrix renormalization group (DMRG), I have studied this system and produced a complex phase diagram.
For the second part of the talk, I will discuss the situation where a dipole is trapped in each lattice site such that the dipole moment vector can be oriented in any direction. The dipoles interact with one another via dipole-dipole potential and also interact with the external field, but they do not hop around between lattice sites. I will talk about some results for this classical model. Then I will explain how I have mapped it to a spin-2 model (which is quantum mechanical) and explain some results obtained using DMRG.
Major Advisor: Dr. Susanne Yelin
Wednesday, June 26, 2019
11:00 AM
Gant Science Complex
GW-103A -
Soroush Khosravi Dehaghi, Department of Physics, University of Connecticut, "Femtosecond Laser Transient Spectroscopy of Carotenoids and Carbon Nanotubes", PhD Defense2:30pm
1/23
Soroush Khosravi Dehaghi, Department of Physics, University of Connecticut, "Femtosecond Laser Transient Spectroscopy of Carotenoids and Carbon Nanotubes", PhD Defense
Wednesday, January 23rd, 2019
02:30 PM - 04:30 PM
Storrs Campus GW103A
Soroush Khosravi Dehaghi,
Department of Physics,
University of Connecticut
Femtosecond Laser Transient Spectroscopy of Carotenoids and Carbon Nanotubes
Carotenoids and semiconducting single-wall carbon nanotubes, which are both nanoscale carbon-based quantum mechanical systems, were studied using different optical spectroscopy techniques.
The lifetime of the S\(_2\) excited state of the carotenoids were estimated using a model-based lifetime analysis routine. It was found that the addition of a conjugated carbonyl group to the carotenoid has several crucial effects on the optical response due to the alteration of the delocalized conjugated \(\pi\) molecular orbital of the molecule. These effects include the shortening of the lifetimes of the excited states, the change in the decay mechanism from the S\(_2\) excited state to the S\(_1\) excited state, and the unresolved vibrational peaks in the steady-state absorption spectrum.
The decay of the E\(_{22}\) excited state of (6,5) semiconducting carbon nanotube dispersed in flavin mononucleotide with water was observed using transient grating spectroscopy. The lifetime of this excited state was estimated to be 450 ± 50 fs. A very strong single-frequency oscillatory component was observed in the transient grating decay profile. -
Electric Form Factor of the Neutron from Asymmetry Measurements, Doctoral Dissertation Oral Defense of Richard Obrecht11:00am
1/4
Electric Form Factor of the Neutron from Asymmetry Measurements, Doctoral Dissertation Oral Defense of Richard Obrecht
Friday, January 4th, 2019
11:00 AM - 12:00 PM
Storrs Campus Gant West, P-121
Electric Form Factor of the Neutron from Asymmetry Measurements
Field of Study: Physics -
Jonathan Kwolek, Department of Physics, University of Connecticut, "Studying Charge Exchange in a Hybrid Ion-neutral Trap", PhD Defense1:30pm
11/30
Jonathan Kwolek, Department of Physics, University of Connecticut, "Studying Charge Exchange in a Hybrid Ion-neutral Trap", PhD Defense
Friday, November 30th, 2018
01:30 PM - 03:30 PM
Storrs Campus GW121
Jonathan Kwolek,
Department of Physics,
University of Connecticut
Studying Charge Exchange in a Hybrid Ion-neutral Trap
Interactions between neutral and ionized atoms are medium-range, and the spiraling nature of these collisions can lead to long interaction times and large cross sections. The field of ion-neutral interactions is bolstered by methods from atomic physics, which allow us to accurately control and determine the quantum-states of the reactants. Atomic physics opens the door to studying these interactions over a large range of energies, in order to observe interesting effects from the ultracold to hot temperature regimes.
The hybrid-trap enables the concentric trapping of a sample of cold atoms and ions. The dissertation discusses our exploration into the controlled reactions in the Na+Ca^+ system, including measurements of sympathetic cooling and a charge-exchange rate which changes as a function of energy and atomic state. The quantum-state distributions of Na in our magneto-optical trap is also explored, as well as its agreement and subsequent deviation based on a predictive model. The measurements of reaction rates indicate a reaction-energy threshold in two different reaction channels, which can be corroborated by theoretical investigation.