Towards a table top quantum computer

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 1999.Includes bibliographical references (leaves 135-139).In the early 1990s, quantum computing proved to be an enticing theoretical possibility but a extremely difficult experimental challenge. Two advances have made experimental quantum computing demonstrable: Quantum error correction; and bulk, thermal quantum computing using nuclear magnetic resonance (NMR). Simple algorithms have been implemented on large, commercial NMR spectrometers that are expensive and cumbersome. The goal of this project is to construct a table-top quantum computer that can match and eventually exceed the performance of commercial machines. This computer should be an inexpensive, easy-to-use machine that can be considered more a computer than its "supercomputer" counterparts. For this thesis, the goal is to develop a low-cost, table-top quantum computer capable of implementing simple quantum algorithms demonstrated thus far in the community, but is also amenable to the many scaling issues of practical quantum computing. Understanding these scaling issues requires developing a theoretical understanding of the signal enhancement techniques and fundamental noise sources of this powerful but delicate system. Complementary to quantum computing, this high performance but low cost NMR machine will be useful for a number of medical, low cost sensing and tagging applications due the unique properties of NMR: the ability to sense and manipulate the information content of materials on macroscopic and microscopic scales.Yael G. Maguire.S.M

Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)

The implicit objective of the biennial "international - Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST) is to foster collaboration between international scientific teams by disseminating ideas through both specific oral/poster presentations and free discussions. For its second edition, the iTWIST workshop took place in the medieval and picturesque town of Namur in Belgium, from Wednesday August 27th till Friday August 29th, 2014. The workshop was conveniently located in "The Arsenal" building within walking distance of both hotels and town center. iTWIST'14 has gathered about 70 international participants and has featured 9 invited talks, 10 oral presentations, and 14 posters on the following themes, all related to the theory, application and generalization of the "sparsity paradigm": Sparsity-driven data sensing and processing; Union of low dimensional subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph sensing/processing; Blind inverse problems and dictionary learning; Sparsity and computational neuroscience; Information theory, geometry and randomness; Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?; Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website: http://sites.google.com/site/itwist1

Bosonic Quantum Simulation in Circuit Quantum Electrodynamics

The development of controllable quantum machines is largely motivated by a desire to simulate quantum systems beyond the capabilities of classical computers. Investigating intrinsically multi-level model bosonic systems, using conventional quantum processors based on two-level qubits is inefficient and incurs a potentially prohibitive mapping overhead in the current near-term intermediate-scale quantum (NISQ) era. This motivates the development of hybrid quantum processors that contain multiple types of degrees of freedom, such that one can leverage an optimal one-to-one mapping between the model system and simulator. Circuit quantum electrodynamics (cQED) has emerged as a leading platform for quantum information processing owing to the immense flexibility of engineering high fidelity coherent interactions and measurements. In cQED, microwave photons act as bosonic particles confined within a nonlinear network of electromagnetic modes. Controlling these photons serves as the basis for a hardware efficient platform for simulation of naturally bosonic systems. In this thesis, we present two experiments that encapsulate this idea by simulating molecular dynamics in two different regimes of electronic-nuclear coupling: adiabatic and nonadiabatic. In the first experiment, we implement a boson sampling protocol for estimating Franck-Condon factors associated with photoelectron spectra. Importantly, we fulfill the scalability requirement by developing a novel single-shot number-resolved quantum non-demolition detector for microwave photons. In the second experiment, we develop and employ a model for simulating dissipative nonadiabatic dynamics through a conical intersection as a basis for modeling photochemical reactions. We directly observe branching of a coherent wave-packet upon passage through the conical intersection, revealing the competition between coherent evolution and dissipation in this system. The tools developed for the experiments in this thesis serve as a basis for implementing more complex bosonic simulations

Sensor Fault Detection and Isolation Using System Dynamics Identification Techniques.

A sensor, generally composed of a power supply, a sensing device, a transducer, and a signal processor, behaves like any other dynamic system. A damage in any of its components can cause unexpected deviations in the sensor measurements from the actual values. Due to its increasing importance in system diagnosis and controls, a faulty sensor may lead to a process shut down or even a fatal accident in safety-critical systems. One of the the challenge is to detect and isolate a fault in the sensor from one in the monitored system once abnormal behaviors are observed in the measurements. This work first tackles such a challenge in a single-input-single-output system by tracking the dynamic response and the associated gain factor of the sensor and the monitored system. Inspired by the fact that sensor measurements depict the dynamics of the monitored plant and the sensor, a subspace identification approach is proposed to detect, isolate, and accommodate a sensor failure under regular operation conditions without additional hardware components. In order to deal with the increased complexity in a multiple-input-multiple-output system, an approach is then proposed to identify the underlying relations in a nonlinear dynamic system with a set of linear models, each capturing the system dynamics in the representative operating regime. Evaluated based on the minimum description length principle, the proposed approach identifies the most correlated system inputs for the target output and the associated model structure using genetic algorithm. An approach is finally developed to detect and isolate sensor faults and air leaks in a diesel engine air path system, a highly dynamic multiple-input-multiple-output system. The proposed approach utilizes analytical redundancies among the intake air mass flow rates and the pressures in the boost and intake manifolds. Without the need for a complete model of the target system, fault detectors are constructed in this work using the growing structure multiple model system identification algorithm. Given the addition information on operation regime from the identified model, the proposed approach evaluates both the global and local properties of the generated residuals to detect and isolate the potential sensor and system faults.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89790/1/jiangli_1.pd

Study on a miniaturized satellite payload for atmospheric temperature measurements

The atmospheric temperature reflects the thermal balance of the atmosphere and is a valuable indicator of climate change. It has been widely recognized that the atmospheric gravity wave activity has a profound effect on the large-scale circulation, thermal and constituent structures in the mesosphere and lower thermosphere (MLT). Temperature distribution in this region is an essential component to identify and quantify gravity waves. Observation from remote sensing instruments on satellite platforms is an effective way to measure the temperature in the MLT region. A miniaturized satellite payload is developed to measure the atmospheric temperature in the MLT region via observing the O2A-band emission. Following a Boltzmann distribution, the relative intensities of the emission lines can be used to derive the temperature profile. Based on the spatial heterodyne spectroscopy, this instrument is capable of resolving individual emission lines in the O2A-band for the spatial and spectral information simultaneously. The monolithic and compact feature of this spectrometer makes it suitable for operating on satellite platforms. In this work, the characterization of the instrument is investigated for the purpose of simultaneously measuring multiple emission lines of the O2A-band. The instrument is explored through a series of experimental methods, providing characteristics of the instrument and evaluation of its performance. In spatial and spectral domain, Level- 0 and Level-1 data processors are developed to convert the raw data to the calibrated spectral radiance for further temperature and gravity wave characterization. Within this framework, the performance of the utilized detector is evaluated along with its radiation tolerance in space environment. In the processor, the detector artifacts are corrected based on the measurements in laboratory or in space. The radiometric response of the instrument is characterized on a pixel-by-pixel basis using a blackbody. An interferogram distortion correction algorithm is developed to correct for the spatial and phase distortion induced by the detector optics. Further, localized phase distortion correction is implemented to correct for the remaining phase error. Unwanted ghost emission lines are removed based on two dimensional Fourier transform. In the spectral domain, the processing steps mainly consist of wavelength calibration and instrument spectral response correction, including filter response correction and modulation efficiency correction. As an in-orbit verification, the AtmoSHINE instrument was successfully deployed in space on 22th of December, 2018. In the first test phase, the functionality and the performance of the instrument in space were verified. The detector dark current measurement in orbit is consistent with the ground-based results. Based on the the calibration procedures and the developed data processing algorithms, the O2A-band emission lines can be successfully resolved. A cross-verification of the AtmoSHINE limb radiance profile with other satellite payload measurements indicates that the radiometric performance of the instrument is within the expectation. The retrieved temperature parameters are studied with respect to different number of samples and different objective functions in the optimization. This work verifies the ability of the instrument to derive the atmospheric temperature in the MLT region and its potential application in gravity wave detections

Engineering coherent control of quantum information in spin systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (p. 151-161).Quantum Information Processing (QIP) promises increased efficiency in computation. A key step in QIP is implementing quantum logic gates by engineering the dynamics of a quantum system. This thesis explores the requirements and methods of coherent control in the context of magnetic resonance for: (i) nuclear spins of small molecules in solution and (ii) nuclear and electron spins in single crystals. The power of QIP is compromised in the presence of decoherence. One method of protecting information from collective decoherence is to limit the quantum states to those respecting the symmetry of the noise. These decoherence-free subspaces (DFS) encode one logical quantum bit (qubit) within multiple physical qubits. In many cases, such as nuclear magnetic resonance (NMR), the control Hamiltonians required for gate engineering leak the information outside the DFS, whereby protection is lost: It is shown how one can still perform universal logic among encoded qubits in the presence of leakage. These ideas are demonstrated on four carbon-13 spins of a small molecule in solution. Liquid phase NMR has shortcomings for QIP, like the lack of strong measurement and low polarization. These two problems can be addressed by moving to solid-state spin systems and incorporating electron spins. If the hyperfine interaction has an anisotropic character, it is proven that the composite system of one electron and N nuclear spins (le-Nn) is completely controllable by addressing only to the electron spin. This 'electron spin actuator' allows for faster gates between the nuclear spins than would be achievable in its absence. In addition, a scheme using logical qubit encodings is proposed for removing the added decoherence due to the electron spin. Lastly, this thesis exemplifies arbitrary gate engineering in a le-ln ensemble solid-sate spin system using a home-built ESR spectrometer designed specifically for engineering high-fidelity quantum control.by Jonathan Stuart Hodges.Ph.D

Multidimensional Frequency Estimation with Applications in Automotive Radar

This thesis considers multidimensional frequency estimation with a focus on computational efficiency and high-resolution capability. A novel framework on multidimensional high-resolution frequency estimation is developed and applied to increase the range, radial velocity, and angular resolution capcability of state-of-the-art automotive radars

Two-proton emission and related phenomena

One of characteristic phenomena for nuclei beyond the proton dripline is the simultaneous emission of two protons (2\emph{p}). The current status of our knowledge of this most recently observed and the least known decay mode is presented. First, different approaches to theoretical description of this process, ranging from effective approximations to advanced three-body models are overviewed. Then, after a brief survey of main experimental methods to produce 2\emph{p}-emitting nuclei and techniques to study their decays, experimental findings in this research field are presented and discussed. This review covers decays of short-lived resonances and excited states of unbound nuclei as well as longer-lived, ground-state radioactive decays. In addition, more exotic decays like three- and four-proton emission are addressed. Finally, related few-body topics, like two-neutron and four-neutron radioactivity, and the problem of the tetraneutron are shortly discussed.Comment: 109 pages, 62 figures, accepted by Progress in Particle and Nuclear Physic

Coherent control of collective atomic spins

In this thesis I explore the use of collective spin angular momentum as a platform for quantum information processing. Such systems have several nice features that make them excellent choices for such protocols, especially ones where information is also stored in photonic variables. The longer coherence times of atoms makes it possible to store information from light in atoms for future use, and it is generally easier to couple atomic variables than to create nonlinear interactions of light. Above and beyond the advantages of atomic systems, collective atomic systems have additional strengths. In the limit of a large number of atoms, the collective variables of atomic systems have a natural connection to the bosonic algebra of light (known as the Holstein-Primakoff or HP approximation) where components of the collective spin angular momentum effectively act as quadratures, making them natural systems for coupling to light. Also, collectively addressing the atoms allows one to access a large state space without individual addressing of the atoms. A natural first step towards control of these collective variables is generating large amounts of atomic spin squeezing. In the HP approximation going from rotations to squeezing corresponds to going from linear to quadratic interactions in the atomic quadratures; for extremely large squeezing one should see the breakdown of the HP approximation and the ability to generate arbitrary collective atomic states. I have sought to improve previous schemes for the spin squeezing of atomic ensembles, such as the proposal of Takeuchi et. al. based on coherent quantum feedback. In this scheme a beam of linearly polarized light passes through the atomic ensemble (prepared in a coherent state), coupling to the atoms through a state-dependent index of refraction (the Faraday effect). The light is then passed through a wave-plate and reflected back through the atoms for a second pass. This double-pass scheme leads to an effective nonlinearity as the atomic fluctuations are mapped onto the light on the first pass and then back on to the atoms in the second pass. The light acts as a bus coupling each atom to each of the others. This nonlinear interaction forms a shearing of the atomic coherent state that results in squeezing. The light is entangled to the atoms through these interactions, and remains entangled as it escapes the system. This leads to decoherence of the atoms as the light is lost to the environment, reducing the amount of spin squeezing achieved. The first step towards improving the double-pass scheme was to add a quantum eraser step in which the light is disentangled from the squeezed atoms. By first measuring one quadrature of the light, and then performing a measurement-dependent rotation on the atomic ensemble, it is possible to decouple the atoms and light so that the loss of the light does not reduce the atomic squeezing. This results in an improvement of the rate of atomic spin squeezing. The nonlinear shearing interaction that remains still falls short of the exponential squeezing seen in optical parametric amplification. The reason for this can be seen by decomposing the shearing interaction into squeezing along a given quadrature followed by a rotation. The rotation leads to a constantly changing axis along which the squeezing occurs, and thus the squeezing builds up more slowly. This can be corrected for by breaking up the light pulse into a sequence of small pulses, and performing a small phase matching rotation after each pulse. The squeezing then adds up along a constant direction, rather than along a constantly varying direction. This results in still further improvement of the rate of atomic spin squeezing. A complete model includes the effects of photon-atom scattering and other noise and loss effects on the overall rate of squeezing. Previous derivations of noise due to photon-atom scattering have started with the unjustified assumptions that the atomic and photonic decoherence channels were both Gaussian and independent of correlations between the two subsystems. They then proceed with very general statistical arguments that rely upon these simplifications. My work begins with the more fundamental master equation picture in which I find the Linblad jump operators. I find that in general the photonic and atomic loss channels are not independent, with the intensity of the light dictating the details of this dependence, and find the conditions under which the Gaussian approximation holds. Squeezing and loss is initially treated assuming ensembles of spin-1/2 atoms, but this work is further extended to higher dimensional subsystems. For a higher spin case, preparing the atoms in spin coherent states is not optimal. One can engineer a stronger interaction by preparing the atoms in an atomic cat state , i.e., a superposition of the two stretch states along the direction of propagation of the light beam. The fluctuations of such a state are more strongly coupled to the light, resulting in a stronger nonlinearity. This leads to strong correlations between the atoms, but they are not immediately useful for squeezing; the cat state must be coherently mapped to a coherent state to achieve atomic spin squeezing. The state created in this manner is ultimately more squeezed than that achieved with the same interaction but prepared initially in a coherent state