Pardis Sahafi | University of Waterloo, Canada (original) (raw)
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Papers by Pardis Sahafi
Achieving atomic resolution is the ultimate limit of magnetic resonance imaging (MRI), and attain... more Achieving atomic resolution is the ultimate limit of magnetic resonance imaging (MRI), and attaining this capability offers enormous technological and scientific opportunities, from drug development to understanding the dynamics in interacting quantum systems. In this work, we present a new approach to nanoMRI utilizing nuclear magnetic resonance diffraction (NMRd) -- a method that extends NMR imaging to probe the structure of periodic spin systems. The realization of NMRd on the atomic scale would create a powerful new methodology for materials characterization utilizing the spectroscopic capabilities of NMR. We describe two experiments that realize NMRd measurement of 31^{31}31P spins in an indium-phosphide (InP) nanowire with sub-Ångstrom precision. In the first experiment, we encode a nanometer-scale spatial modulation of the zzz-axis magnetization by periodically inverting the 31^{31}31P spins, and detect the period and position of the modulation with a precision of <0.8<0.8<0.8 Å. In the second experiment, we demonstrate an interferometric technique, utilizing NMRd, for detecting an Ångstrom-scale displacement of the InP sample with a precision of 0.07 Å. The diffraction-based techniques developed in this work represent new measurement modalities in NMR for probing the structure and dynamics of spins on sub-Ångstrom length scales, and demonstrate the feasibility of crystallographic MRI measurements.
Adiabatic operations are powerful tools for robust quantum control in numerous fields of physics,... more Adiabatic operations are powerful tools for robust quantum control in numerous fields of physics, chemistry and quantum information science. The inherent robustness due to adiabaticity can, however, be impaired in applications requiring short evolution times. We present a single versatile gradient-based optimization protocol that combines adiabatic control with effective Hamiltonian engineering in order to design adiabatic operations tailored to the specific imperfections and resources of an experimental setup. The practicality of the protocol is demonstrated by engineering a fast, 2.3 Rabi cycle-long adiabatic inversion pulse for magnetic resonance with built-in robustness to Rabi field inhomogeneities and resonance offsets. The performance and robustness of the pulse is validated in a nanoscale force-detected magnetic resonance experiment on a solid-state sample, indicating an ensemble-averaged inversion accuracy of sim99.997\sim 99.997\%sim99.997. We further showcase the utility of our protocol ...
I venture into the study of electron pumps in order to develop a more comprehensive understanding... more I venture into the study of electron pumps in order to develop a more comprehensive understanding of the operation of these devices. We investigate the charging and relaxation of electrons within the dot . For research on charge relaxation of the dot we use devices where the point contact is coupled to the QD in order to probe the charge occupation of the dot. The devices are investigated and considered as possible single detectors of terahertz radiation. The phenomena related to propagating electrons through pumps were explored. We measured and analysed both the dwell times and the excitation states within the dot. The theoretical model of the device is discussed in relation to the study. The electron dwell times are mapped and we show the effects of applied magnetic field on them. A multi-electron quantum dot is considered as a direct terahertz detectors in the investigation of the electron pump as an emitter. A few hundred electrons occupy the dot. The dot is charge excited by ab...
In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sens... more In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sensitive cantilevers in a number of unique scanning probe microscopy (SPM) settings. We describe the fabrication of ultra-low dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning probe applications. Our fabrication process produces, with high yield, ultra-high aspect ratio vertical SiNWs that exhibit exceptional force sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited force sensitivity of 9.7 ± 0.4 aN/ √ Hz at room temperature and 500 ± 20 zN/ √ Hz at 4 K. To facilitate their use in SPM, the SiNWs are patterned within 7 µm from the edge of the substrate, allowing convenient optical access for displacement detection.
Achieving atomic resolution is the ultimate limit of magnetic resonance imaging (MRI), and attain... more Achieving atomic resolution is the ultimate limit of magnetic resonance imaging (MRI), and attaining this capability offers enormous technological and scientific opportunities, from drug development to understanding the dynamics in interacting quantum systems. In this work, we present a new approach to nanoMRI utilizing nuclear magnetic resonance diffraction (NMRd) -- a method that extends NMR imaging to probe the structure of periodic spin systems. The realization of NMRd on the atomic scale would create a powerful new methodology for materials characterization utilizing the spectroscopic capabilities of NMR. We describe two experiments that realize NMRd measurement of 31^{31}31P spins in an indium-phosphide (InP) nanowire with sub-Ångstrom precision. In the first experiment, we encode a nanometer-scale spatial modulation of the zzz-axis magnetization by periodically inverting the 31^{31}31P spins, and detect the period and position of the modulation with a precision of <0.8<0.8<0.8 Å. In the second experiment, we demonstrate an interferometric technique, utilizing NMRd, for detecting an Ångstrom-scale displacement of the InP sample with a precision of 0.07 Å. The diffraction-based techniques developed in this work represent new measurement modalities in NMR for probing the structure and dynamics of spins on sub-Ångstrom length scales, and demonstrate the feasibility of crystallographic MRI measurements.
Adiabatic operations are powerful tools for robust quantum control in numerous fields of physics,... more Adiabatic operations are powerful tools for robust quantum control in numerous fields of physics, chemistry and quantum information science. The inherent robustness due to adiabaticity can, however, be impaired in applications requiring short evolution times. We present a single versatile gradient-based optimization protocol that combines adiabatic control with effective Hamiltonian engineering in order to design adiabatic operations tailored to the specific imperfections and resources of an experimental setup. The practicality of the protocol is demonstrated by engineering a fast, 2.3 Rabi cycle-long adiabatic inversion pulse for magnetic resonance with built-in robustness to Rabi field inhomogeneities and resonance offsets. The performance and robustness of the pulse is validated in a nanoscale force-detected magnetic resonance experiment on a solid-state sample, indicating an ensemble-averaged inversion accuracy of sim99.997\sim 99.997\%sim99.997. We further showcase the utility of our protocol ...
I venture into the study of electron pumps in order to develop a more comprehensive understanding... more I venture into the study of electron pumps in order to develop a more comprehensive understanding of the operation of these devices. We investigate the charging and relaxation of electrons within the dot . For research on charge relaxation of the dot we use devices where the point contact is coupled to the QD in order to probe the charge occupation of the dot. The devices are investigated and considered as possible single detectors of terahertz radiation. The phenomena related to propagating electrons through pumps were explored. We measured and analysed both the dwell times and the excitation states within the dot. The theoretical model of the device is discussed in relation to the study. The electron dwell times are mapped and we show the effects of applied magnetic field on them. A multi-electron quantum dot is considered as a direct terahertz detectors in the investigation of the electron pump as an emitter. A few hundred electrons occupy the dot. The dot is charge excited by ab...
In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sens... more In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sensitive cantilevers in a number of unique scanning probe microscopy (SPM) settings. We describe the fabrication of ultra-low dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning probe applications. Our fabrication process produces, with high yield, ultra-high aspect ratio vertical SiNWs that exhibit exceptional force sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited force sensitivity of 9.7 ± 0.4 aN/ √ Hz at room temperature and 500 ± 20 zN/ √ Hz at 4 K. To facilitate their use in SPM, the SiNWs are patterned within 7 µm from the edge of the substrate, allowing convenient optical access for displacement detection.