Theses - Physics
http://hdl.handle.net/1721.1/7865
2018-05-21T18:27:30ZStrongly interacting photons via Rydberg-Rydberg interactions
http://hdl.handle.net/1721.1/115027
Strongly interacting photons via Rydberg-Rydberg interactions
Liang, Qiyu, Ph. D. Massachusetts Institute of Technology
A quantum nonlinear optical medium, i.e. a medium where the light propagation depends on photon number, has been a long-standing goal due to its applications in quantum information, communication and metrology. When the medium is nonlinear at single photon level, it can be viewed as strong interactions between individual photons mediated by the medium. Here, we achieve such strong interactions by coupling the photons to highly polarizable Rydberg states with a phenomena called electromagnetically induced transparency (EIT). The strong van der Waals or dipole-dipole interactions between Rydberg excitations map to the photons under EIT conditions. The photons are incident on a cigar-shaped laser-cooled rubidium cloud in free space. After the photons emerge out of the cloud, we measure the photon correlations from time-resolved single photon detections, which reveal crucial information about the quantum states of strongly interacting two or three photons. In this thesis, I will present four experiments. The first two experiments demonstrate quantum nonlinearities with a propagating continuous wave (cw) light field via Rydberg-Rydberg interactions in the dissipative and dispersive regimes, respectively. In the dissipative regime, strong photon anti-bunching is observed. In the dispersive regime, we achieve a conditional phase shift ~ [pi]/4, together with photon-bunching driven by attractive force. Moreover, the photons acquire a finite mass and we see evidence for a diphoton molecule. In the third experiment, by measuring higher-order correlation functions, we observe a three-photon bound state evidenced by tighter binding in addition to a larger conditional phase shift than the two-photon states. By comparing with an effective field theory, our results suggest that there might be a three-photon force on top of the pairwise interactions owing to the saturation of the interaction. Namely, only one Rydberg excitation can be created within a characteristic length scale called blockade radius. Finally, we explore the exchange interaction instead of the widely studied blockade shifts. Under the exchange interactions, a propagating photon and a stored one experience coherent collisions protected by a symmetry of the Hamiltonian and pick up a robust [pi]/2 phase shift.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 181-188).
2017-01-01T00:00:00ZTop mass determination using Effective Field Theories
http://hdl.handle.net/1721.1/115026
Top mass determination using Effective Field Theories
Pathak, Aditya, Ph. D. Massachusetts Institute of Technology
The top quark mass is one of the most important Standard Model parameters and its mass has been measured at sub-percent precision by the Tevatron and LHC using Monte Carlo (MC) based methods. The resulting MC top mass parameter suffers from 0(1 GeV) uncertainty due to lack of specification of a precise field theoretic definition. Here a kinematic extraction method for obtaining a precisely defined short distance top mass at the LHC is proposed. A formula for factorized top jet mass cross section in the peak region is derived using methods of Effective Field Theory (EFT). It can then be used for direct comparison with data or for calibrating Monte Carlo simulations. Result for hard matching coefficient at two loops at the top mass scale is presented that enables N3LL logarithmic resumamtion of the cross section for top-jets in e+e- collisions. An effective theory setup for top mass extraction with soft drop grooming is derived, and is used to derive a factorization formula for the groomed jet mass distribution. Constraints from power counting in EFT limit the strength of groomers to "light grooming region". Studies with PYTHIA demonstrate that application of soft drop, even when restricted to light grooming, shows remarkable improvements in resilience to contamination from the underlying event (UE), has vastly reduced dependence the jet radius, and makes the top jet mass spectrum from pp collisions look like that of e+e- collisions as predicted. Modifications to the peaked spectrum from hadronization and UE for groomed top jets are suppressed and can be handled reliably. Using our factorization theorem results, a preliminary calibration study of Pythia top mass parameter is performed that yields results consistent with earlier calibrations for e+e- colliders.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 231-239).
2017-01-01T00:00:00ZQuantum signal processing by single-qubit dynamics
http://hdl.handle.net/1721.1/115025
Quantum signal processing by single-qubit dynamics
Low, Guang Hao
Quantum computation is the most powerful realizable model of computation, and is uniquely positioned to solve specialized problems intractable to classical computers. This quantum advantage arises from directly exploiting the strangeness of quantum mechanics that is fundamental to reality. As such, one expects our understanding of quantum processes in physical systems to be indispensable to the design and execution of quantum algorithms. We present quantum signal processing, which exploits the dynamics of simple quantum systems to perform non-trivial computations. Such systems applied as computational modules in larger quantum algorithms, offer a natural physical alternative to standard tasks such as the calculation of elementary functions with integer arithmetic. The quantum advantage of this approach, based on simple physics, is of significant practical relevance. In cases, arbitrary bits of precision may be emulated using only constant space. Moreover, the simplicity and performance of quantum signal processing is such that it is the final missing ingredient for realizing a number of optimal quantum algorithms, particularly in Hamiltonian simulation. Quantum signal processing realizes a useful fusion of analog and digital models of quantum computation. At the physical level, we focus on how even a simple two-level system - the qubit, computes through optimal discrete-time quantum control. Whereas quantum control is typically used to synthesize unitary quantum gates, we solve the synthesis problem of unitary quantum functions with a fully characterization of achievable functions, and efficient techniques for their implementation. This furnishes a surprisingly rich framework in the analog model of quantum computation for computing functions. The generality of this model is realized by many applications, often with no modification, to quantum algorithms designed for digital quantum computers, in particular for matrix manipulation. In this manner, we solve a number of open problem related to optimal amplitude amplification algorithms, optimally computing on matrices with a quantum computer, and the simulation of physical systems.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 117-125).
2017-01-01T00:00:00ZDetectability of dynamical tidal effects and the detection of gravitational-wave transients with LIGO
http://hdl.handle.net/1721.1/115024
Detectability of dynamical tidal effects and the detection of gravitational-wave transients with LIGO
Essick, Reed Clasey
Dynamical tidal effects impact the orbital motion of extended bodies, imprinting themselves in several measurable ways. This thesis explores the saturation of weakly nonlinear dynamical tidal interactions within two very different systems: hot Jupiters orbiting main-sequence hosts with radiative cores and compact stellar remnants inspiraling due to gravitational radiation. In addition, it discusses general aspects of detecting Gravitational Waves with ground-based laser interferometers. Data quality and noise reduction along with source parameter estimation, with particular emphasis on localization, are discussed in great detail. Conclusions drawn from statistical ensembles of simulated signals are applied to the first three confirmed detections of Gravitational Waves, all from the coalescence of binary black hole systems.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 186-201).
2017-01-01T00:00:00Z