Event
Ph.D. Defense: Harjot Singh
Wednesday, April 5, 2023
10:30 a.m.
ERP 1207 (Ireap Large conference room)
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Thesis Defense
Name: Harjot Singh
Committee:
Professor Edo Waks (Chair)
Professor Mohammad Hafezi
Professor Julius Goldhar
Professor Cheng Gong
Professor John Cummings
Date/time: 04/05/2023 10:30am-12pm
Location: ERP 1207 (Ireap Large conference room)
Title: Strong optical nonlinearity and spin control using photonic structures
Abstract: Photons are excellent carriers of quantum information. Since they hardly interact with each other, they can maintain their quantum state over long distances. However, this poses a challenge if one wishes to create entanglement between the degrees of freedom of photons. Creating entangled states of photons is essential for quantum information processing with photons.
One way to create interactions between photons is to create strong interactions between two level atoms and modes of electromagnetic radiation. This can be achieved by coupling optical transitions of two-level atoms with modes of optical cavities or waveguides. The nonlinearity of a two-level atom then effectively mediates interactions between two (or more) photons. However, due to a fundamental time-bandwidth limit, a two-level atom cannot enable arbitrary quantum operations on the states of two photons.
In this thesis, we study theoretically the problem of splitting two distinguishable photons to distinguishable output modes with a two-level atom. Due to the time-bandwidth limit, the achieved splitting efficiency is fundamentally limited to 82% using just a two-level atom. We show that a linear optical unitary transformation on the output modes of the two-level atom can exceed this limit. Via optimization of the input two photon wavefunction and the parameters of the linear optical unitary, we calculated a splitting efficiency of 92%.
For experimental realization of strong atom-light interactions, we used InGaAsquantum dots coupled to a bullseye cavity. Bullseye cavities are promising towards realization of efficient collection of light due to their near Gaussian far field emission. We demonstrated a strong interaction between the quantum dot exciton and the Bullseye cavity mode, quantified by a Cooperativity of ~8. This high cooperativity with a low-quality factor cavity can be attributed to the charge stabilization enabled by the diode heterostructure of the quantum dot samples we used.
Finally, we focus on the electron spin ground states of a negatively charged InGaAs quantum dot. The electron spin interacts with the nuclear spins of the In, Ga and As. We measure the spectrum of this interaction using all optical dynamical decoupling pulse sequencies. This work lays a path forward to realizing efficient and coherent spin-photon interfaces with InGaAs quantum dots.
