Department of Physics
http://hdl.handle.net/1721.1/7864
2016-02-08T06:05:57ZCumulative effects in quantum algorithms and quantum process tomography
http://hdl.handle.net/1721.1/100678
Cumulative effects in quantum algorithms and quantum process tomography
Hess, Shelby Kimmel
This thesis comprises three results on quantum algorithms and quantum process tomography. In the first section, I create a tool that uses properties of the quantum general adversary bound to upper bound the query complexity of Boolean functions. Using this tool I prove the existence of O(1)-query quantum algorithms for a set of functions called FAULT TREES. To obtain these results, I combine previously known properties of the adversary bound in a new way, as well as extend an existing proof of a composition property of the adversary bound. The second result is a method for characterizing errors in a quantum computer. Many current tomography procedures give inaccurate estimates because they do not have adequate methods for handling noise associated with auxiliary operations. The procedure described here provides two ways of dealing with this noise: estimating the noise independently so its effect can be completely understood, and analyzing the worst case effect of this noise, which gives better bounds on standard estimates. The final section describes a quantum analogue of a classical local search algorithm for Classical k-SAT. I show that for a restricted version of Quantum 2-SAT, this quantum algorithm succeeds in polynomial time. While the quantum algorithm ultimately performs similarly to the classical algorithm, quantum effects, like the observer effect, make the analysis more challenging.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 129-134).
2014-01-01T00:00:00ZPhotomultiplier tube calibration for the Cubic Meter Dark Matter Time Projection Chamber
http://hdl.handle.net/1721.1/100342
Photomultiplier tube calibration for the Cubic Meter Dark Matter Time Projection Chamber
Burdge, Kevin (Kevin Brian)
This thesis concerns measurements I performed on photomultiplier tubes (PMTs) and lenses to be used in the Cubic Meter Dark Matter Time Projection Chamber (DMTPC) experiment. DMTPC is a new generation of detector, which takes the idea of a standard time projection chamber and adds in some additional optical elements, such as CCDs and PMTs. The goal of DMTPC is the directional detection of the dark matter. During the course of my measurements, I characterized both the absolute gains of DMTPC's eight PMTs, as well as the dark currents exhibited by each of the PMTs. Seven of the eight PMTs demonstrated gains on the order of 10 6-10 7, and one PMT did not function at all. Of the seven working PMTs, six of them had dark currents under 10 kHz, and one had an excessively high dark current over 10 kHz. These gain values for the PMTs will give DMTPC the means to measure the Z dimensions of the particle tracks it intends to image, and thus when combined with the information from the CCDs will allow for full track reconstruction. DMTPC will use lenses on their CCD cameras, and I also measured the transparency of these lenses, and discovered that they are opaque below approximately 350nm. These measurements will be essential for DMTPC, because they will provide information about the relative amounts of light the PMTs and CCDs on the detector will register, and thus provide key information for track reconstruction.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 45-46).
2015-01-01T00:00:00ZLocalization, escape rate and delocalization in kinked ratchet potentials
http://hdl.handle.net/1721.1/100341
Localization, escape rate and delocalization in kinked ratchet potentials
Choi, Sang Hyun
The particle localization in ratchet potentials with segments of reverse directions, or kinked ratchets, is computationally studied. Kinks localize a particle on on-off pulsating ratchet potentials, forming stable points in the effective potential. Analogous Kramers rate for transition between kinks is derived through simulations under different values of parameters defining the system. Adding tilting to the system with a proper choice of tilting frequency induces stochastic resonance. Delocalization of a particle is observed in the resonant activation regime.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 45-46).
2015-01-01T00:00:00ZHigh-precision electron-spin sensing with ensembles of nitrogen-vacancy centers in diamond
http://hdl.handle.net/1721.1/100340
High-precision electron-spin sensing with ensembles of nitrogen-vacancy centers in diamond
Đorđević, Tamara
This thesis describes physical background and an experimental realization of a bulk diamond magnetic field and temperature sensor. The sensing is done using continuous-wave electron-spin resonance spectra of nitrogen-vacancy centers in diamond. Experiments were performed using a light-trapping diamond waveguide sample, with which we estimate to address 10¹³ nitrogen-vacancy centers simultaneously. We derive energy level structure of a nitrogen-vacancy center and recover resonant frequencies of the ESR spectrum. Using the Lindblad master equation, we model ESR line-shape and for the first time consider the influence of infrared driving on the ESR contrast. Both continuous-wave and pulsed sensing protocols are described, and a novel reference-free temperature sensing scheme is proposed. In addition to building a laboratory setup for sensing, we discuss how to miniaturize the setup components and make an on-chip diamond sensor. In particular, we optimize the on-chip fluorescence collection apparatus. Finally, using the built laboratory setup, we demonstrate magnetic field sensitivity floor on the order of 1 nT/Hz 1/2 and temperature sensitivity floor of 0.3 mK/Hz 1/2.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 81-83).
2015-01-01T00:00:00Z