Papers by Sophie Schirmer
Journal of Applied Physics, Dec 11, 2017
Spin-based logic devices could operate at very high speed with very low energy consumption and ho... more Spin-based logic devices could operate at very high speed with very low energy consumption and hold significant promise for quantum information processing and metrology. Here, an in-house developed, experimentally verified, ensemble self-consistent Monte Carlo device simulator with a Bloch equation model using a spin-orbit interaction Hamiltonian accounting for Dresselhaus and Rashba couplings is developed and applied to a spin field effect transistor (spinFET) operating under externally applied voltages on a gate and a drain. In particular, we simulate electron spin transport in a 25 nm gate length In0.7Ga0.3As metal-oxide-semiconductor field-effect transistor (MOSFET) with a CMOS compatible architecture. We observe non-uniform decay of the net magnetization between the source and gate and a magnetization recovery effect due to spin refocusing induced by a high electric field between the gate and drain. We demonstrate coherent control of the polarization vector of the drain current via the source-drain and gate voltages, and show that the magnetization of the drain current is strain-sensitive and can be increased twofold by strain induced into the channel.
Semiconductor Science and Technology
Spin-based metal-oxide-semiconductor field-effect transistors (MOSFETs) with a high-mobility III-... more Spin-based metal-oxide-semiconductor field-effect transistors (MOSFETs) with a high-mobility III-V channel are studied using self-consistent quantum corrected ensemble Monte Carlo device simulations of charge and spin transport. The simulations including spin–orbit coupling mechanisms (Dresselhaus and Rashba coupling) examine the electron spin transport in the 25 nm gate length I n 0.7 G a 0.3 A s MOSFET. The transistor lateral dimensions (the gate length, the source-to-gate, and the gate-to-drain spacers) are increased to investigate the spin-dependent drain current modulation induced by the gate from room temperature of 300 K down to 77 K. This modulation increases with increasing temperature due to increased Rashba coupling. Finally, an increase of up to 20 nm in the gate length, source-to-gate, or the gate-to-drain spacers increases the spin polarization and enhances the spin-dependent drain current modulation at the drain due to polarization-refocusing effects.
AVS quantum science, Jul 1, 2024
IEEE Control Systems Letters, Dec 31, 2023
Physical review research, Oct 1, 2023
Research Directions: Quantum Technologies
As shown in previous work, in some cases closed quantum systems exhibit a non-conventional absenc... more As shown in previous work, in some cases closed quantum systems exhibit a non-conventional absence of trade-off between performance and robustness in the sense that controllers with the highest fidelity can also provide the best robustness to parameter uncertainty. As the dephasing induced by the interaction of the system with the environment guides the evolution to a more classically mixed state, it is worth investigating what effect the introduction of dephasing has on the relationship between performance and robustness. In this paper we analyze the robustness of the fidelity error, as measured by the logarithmic sensitivity function, to dephasing processes. We show that introduction of dephasing as a perturbation to the nominal unitary dynamics requires a modification of the log-sensitivity formulation used to measure robustness about an uncertain parameter with nonzero nominal value used in previous work. We consider controllers optimized for a number of target objectives rangin...
MR MEGA-PRESS spectra quantification with convolutional neural networks, written in Python using ... more MR MEGA-PRESS spectra quantification with convolutional neural networks, written in Python using Keras with Tensorflow.<br>
IEEE Control Systems Letters, 2023
Recent achievements in quantum control have resulted in advanced techniques for designing control... more Recent achievements in quantum control have resulted in advanced techniques for designing controllers for applications in quantum communication, computing, and sensing. However, the susceptibility of such systems to noise and uncertainties necessitates robust controllers that perform effectively under these conditions to realize the full potential of quantum devices. The timedomain log-sensitivity and a recently introduced robustness infidelity measure (RIM) are two means to quantify controller robustness in quantum systems. The former can be found analytically, while the latter requires Monte-Carlo sampling. In this work, the correlation between the logsensitivity and the RIM for evaluating the robustness of single excitation transfer fidelity in spin chains and rings in the presence of dephasing is investigated. We show that the expected differential sensitivity of the error agrees with the differential sensitivity of the RIM, where the expectation is over the error probability distribution. Statistical analysis also demonstrates that the log-sensitivity and the RIM are linked via the differential sensitivity, and that the differential sensitivity and RIM are highly concordant. This unification of two means (one analytic and one via sampling) to assess controller robustness in a variety of realistic scenarios provides a first step in unifying various tools to model and assess robustness of quantum controllers.
This project consists of code and data to facilitate investigation of the robustness of energy la... more This project consists of code and data to facilitate investigation of the robustness of energy landscape controllers for transporting a single excitation in XX-coupled spin-1/2 rings of size 5 and 6 under decoherence. The dataset provides controllers optimized for three different performance objectives, and the analysis code is designed to investigate robustness through both statistical estimation and analytic calculation of the log-sensitivity of the fidelity error.
arXiv (Cornell University), Aug 30, 2016
The aim of this work was to create tissue-mimicking gel phantoms appropriate for diffusion kurtos... more The aim of this work was to create tissue-mimicking gel phantoms appropriate for diffusion kurtosis imaging (DKI) for quality assurance, protocol optimization and sequence development. Methods: A range of agar, agarose and polyvinyl alcohol phantoms with concentrations ranging from 1.0% to 3.5%, 0.5% to 3.0% and 10% to 20%, respectively, and up to 3 g of glass microspheres per 100 ml were created. Diffusion coefficients, excess kurtosis values and relaxation rates were experimentally determined. Results: The kurtosis values for the plain gels ranged from 0.05 with 95% confidence interval (CI) of (0.029, 0.071) to 0.216(0.185, 0.246), well below the kurtosis values reported in the literature for various tissues. The addition of glass microspheres increased the kurtosis of the gels with values up to 0.523(0.465, 0.581) observed for gels with the highest concentration of microspheres. Repeat scans of some of the gels after more than six months of storage at room temperature indicate changes in the diffusion parameters of less than 10%. The addition of the glass microspheres reduces the apparent diffusion coefficients (ADCs) and increases the longitudinal and transverse relaxation rates but the values remain comparable to those for plain gels and tissue, with ADCs observed ranging from 818(585, 1053) × 10 −6 mm 2 /s to 2257(2118, 2296) × 10 −6 mm 2 /s, and R 1 values ranging from 0.34(0.32, 0.35) 1/s to 0.51(0.50, 0.52) 1/s, and R 2 values ranging from 9.69(9.34, 10.04) 1/s to 33.07(27.10, 39.04) 1/s. Conclusions: Glass microspheres can be used to effectively modify diffusion properties of gel phantoms and achieve a range of kurtosis values comparable to those reported for a variety of tissues.
Physica Medica, Sep 1, 2016
differentiate between normal and pathologic cases and also related to type of scoliosis. Results.... more differentiate between normal and pathologic cases and also related to type of scoliosis. Results. Skin temperature distribution and homogeneity were quantitatively characterized. Temperature homogeneity is altered as a consequence of scoliosis, between the concave and convex sides of the spine curvature. Alterations tend to depend on the degree of scoliosis. The combination of parameters resulting from thermographic image analysis can effectively describe skin temperature pattern. Conclusion. Image analysis techniques can reveal alterations of skin temperature distribution due to scoliisis. Thermography has the potential to serve as a complementary tool on the evaluation of scoliosis development and treatment.
Magnetic Resonance Imaging, Apr 1, 2018
Evaluation of diffusion weighted imaging in the context of multi-parametric MRI of the prostate i... more Evaluation of diffusion weighted imaging in the context of multi-parametric MRI of the prostate in the assessment of suspected low volume prostatic carcinoma.
Radiotherapy and Oncology, May 1, 2017
Released under the terms of a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Intern... more Released under the terms of a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC-BY-NC-ND).
Research Directions: Quantum Technologies
The design and analysis of controllers to regulate excitation transport in quantum spin rings pre... more The design and analysis of controllers to regulate excitation transport in quantum spin rings presents challenges in the application of classical feedback control techniques to synthesize effective control and generates results in contradiction to the expectations of classical control theory. This paper examines the robustness of controllers designed to optimize the fidelity of an excitation transfer to uncertainty in system and control parameters. We use the logarithmic sensitivity of the fidelity error as the robustness measure, drawing on the classical control analog of the sensitivity of the tracking error. Our analysis shows that quantum systems optimized for coherent transport demonstrate significantly different correlation between error and the log-sensitivity depending on whether the controller is optimized for readout at an exact time T or over a time-window T ± Δ/2.
arXiv (Cornell University), Apr 19, 2023
We propose a model-based reinforcement learning (RL) approach for noisy time-dependent gate optim... more We propose a model-based reinforcement learning (RL) approach for noisy time-dependent gate optimization with reduced sample complexity over model-free RL. Sample complexity is defined as the number of controller interactions with the physical system. Leveraging an inductive bias, inspired by recent advances in neural ordinary differential equations (ODEs), we use an auto-differentiable ODE, parametrized by a learnable Hamiltonian ansatz, to represent the model approximating the environment, whose time-dependent part, including the control, is fully known. Control alongside Hamiltonian learning of continuous time-independent parameters is addressed through interactions with the system. We demonstrate an order of magnitude advantage in sample complexity of our method over standard model-free RL in preparing some standard unitary gates with closed and open system dynamics, in realistic computational experiments incorporating single shot measurements, arbitrary Hilbert space truncations, and uncertainty in Hamiltonian parameters. Also, the learned Hamiltonian can be leveraged by existing control methods like GRAPE for further gradient-based optimization with the controllers found by RL as initializations. Our algorithm, which we apply to nitrogen vacancy (NV) centers and transmons, is well suited for controlling partially characterized one-and two-qubit systems.
arXiv (Cornell University), Mar 9, 2023
As shown in previous work, in some cases closed quantum systems exhibit a non-conventional absenc... more As shown in previous work, in some cases closed quantum systems exhibit a non-conventional absence of trade-off between performance and robustness in the sense that controllers with the highest fidelity can also provide the best robustness to parameter uncertainty. As the dephasing induced by the interaction of the system with the environment guides the evolution to a more classically mixed state, it is worth investigating what effect the introduction of dephasing has on the relationship between performance and robustness. In this paper we analyze the robustness of the fidelity error, as measured by the logarithmic sensitivity function, to dephasing processes. We show that introduction of dephasing as a perturbation to the nominal unitary dynamics requires a modification of the log-sensitivity formulation used to measure robustness about an uncertain parameter with non-zero nominal value used in previous work. We consider controllers optimized for a number of target objectives ranging from fidelity under coherent evolution to fidelity under dephasing dynamics to determine the extent to which optimizing for a specific regime has desirable effects in terms of robustness. Our analysis is based on two independent computations of the log-sensitivity: a statistical Monte Carlo approach and an analytic calculation. We show that despite the different log-sensitivity calculations employed in this study, both demonstrate that the log-sensitivity of the fidelity error to dephasing results in a conventional trade-off between performance and robustness.
This project consists of code and data to facilitate investigation of the robustness of energy la... more This project consists of code and data to facilitate investigation of the robustness of energy landscape controllers for transporting a single excitation in XX-coupled spin-1/2 rings of size 5 and 6 under decoherence. The dataset provides controllers optimized for three different performance objectives, and the analysis code is designed to investigate robustness through both statistical estimation and analytic calculation of the log-sensitivity of the fidelity error.
arXiv (Cornell University), Jul 15, 2022
Robustness of quantum operations or controls is important to build reliable quantum devices. The ... more Robustness of quantum operations or controls is important to build reliable quantum devices. The robustness-infidelity measure (RIMp) is introduced to statistically quantify in a single measure the robustness and fidelity of a controller as the p-th order Wasserstein distance between the fidelity distribution of the controller under any uncertainty and an ideal fidelity distribution. The RIMp is the p-th root of the p-th raw moment of the infidelity distribution. Using a metrization argument, we justify why RIM1 (the average infidelity) is a good practical robustness measure. Based on the RIMp, an algorithmic robustness-infidelity measure (ARIM) is developed to quantify the expected robustness and fidelity of controllers found by a control algorithm. The utility of the RIM and ARIM is demonstrated on energy landscape controllers of spin-1 2 networks subject to Hamiltonian uncertainty. The robustness and fidelity of individual controllers as well as the expected robustness and fidelity of controllers found by different popular quantum control algorithms are characterized. For algorithm comparisons, stochastic and non-stochastic optimization objectives are considered. Although high fidelity and robustness are often conflicting objectives, some high-fidelity, robust controllers can usually be found, irrespective of the choice of the quantum control algorithm. However, for noisy or stochastic optimization objectives, adaptive sequential decision-making approaches, such as reinforcement learning, have a cost advantage compared to standard control algorithms and, in contrast, the high infidelities obtained are more consistent with high RIM values for low noise levels.
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Papers by Sophie Schirmer