Enhancement of electron spin coherence by optical preparation of nuclear spins

We study a large ensemble of nuclear spins interacting with a single electron spin in a quantum dot under optical excitation and photon detection. When a pair of applied laser fields satisfy two-photon resonance between the two ground electronic spin states, detection of light scattering from the intermediate exciton state acts as a weak quantum measurement of the effective magnetic (Overhauser) field due to the nuclear spins. If the spin were driven into a coherent population trapping state where no light scattering takes place, then the nuclear state would be projected into an eigenstate of the Overhauser field operator and electron decoherence due to nuclear spins would be suppressed: we show that this limit can be approached by adapting the laser frequencies when a photon is detected. We use a Lindblad equation to describe the time evolution of the driven system under photon emission and detection. Numerically, we find an increase of the electron coherence time from 5 ns to 500 ns after a preparation time of 10 microseconds.Comment: 5 pages, 4 figure

Charge radii of the nucleon from its flavor dependent Dirac form factors

We have determined the proton and the neutron charge radii from a global analysis of the proton and the neutron elastic form factors, after first performing a flavor decomposition of these form factors under charge symmetry in the light cone frame formulation. We then extracted the transverse mean-square radii of the flavor dependent quark distributions. In turn, these are related in a model-independent way to the proton and neutron charge radii but allow us to take into account motion effects of the recoiling nucleon for data at finite but high momentum transfer. In the proton case we find $\langle r_p \rangle = 0.852 \pm0.002_{\rm (stat.)} \pm0.009_{\rm (syst.)}~({\rm fm})$, consistent with the proton charge radius obtained from muonic hydrogen spectroscopy \cite{pohl:2010,antog2013}. The current method improves on the precision of the $\langle r_p \rangle$ extraction based on the form factor measurements. Furthermore, we find no discrepancy in the $\langle r_p \rangle$ determination among the different electron scattering measurements, all of which, utilizing the current method of extraction, result in a value that is consistent with the smallest $\langle r_p \rangle$ extraction from the electron scattering measurements \cite{Xiong:2019umf}. Concerning the neutron case, past results relied solely on the neutron-electron scattering length measurements, which suffer from an underestimation of underlying systematic uncertainties inherent to the extraction technique. Utilizing the present method we have performed the first extraction of the neutron charge radius based on nucleon form factor data, and we find $\langle r_n^2 \rangle = -0.122 \pm0.004_{\rm (stat.)} \pm0.010_{\rm (syst.)}~({\rm fm}^2)$

A High-resolution Scintillating Fiber Tracker With Silicon Photomultiplier Array Readout

We present prototype modules for a tracking detector consisting of multiple layers of 0.25 mm diameter scintillating fibers that are read out by linear arrays of silicon photomultipliers. The module production process is described and measurements of the key properties for both the fibers and the readout devices are shown. Five modules have been subjected to a 12 GeV/c proton/pion testbeam at CERN. A spatial resolution of 0.05 mm and light yields exceeding 20 detected photons per minimum ionizing particle have been achieved, at a tracking efficiency of more than 98.5%. Possible techniques for further improvement of the spatial resolution are discussed.Comment: 31 pages, 27 figures, pre-print version of an article published in Nuclear Instruments and Methods in Physics Research Section A, Vol. 62

Observation of Faraday rotation from a single confined spin

Ability to read-out the state of a single confined spin lies at the heart of solid-state quantum information processing. While all-optical spin measurements using Faraday rotation has been successfully implemented in ensembles of semiconductor spins, read-out of a single semiconductor spin has only been achieved using transport measurements based on spin-charge conversion. Here, we demonstrate an all-optical dispersive measurement of the spin-state of a single electron trapped in a semiconductor quantum dot. We obtain information on the spin state through conditional Faraday rotation of a spectrally detuned optical field, induced by the polarization- and spin-selective trion (charged quantum dot) transitions. To assess the sensitivity of the technique, we use an independent resonant laser for spin-state preparation. An all-optical dispersive measurement on single spins has the important advantage of channeling the measurement back-action onto a conjugate observable, thereby allowing for repetitive or continuous quantum nondemolition (QND) read-out of the spin-state. We infer from our results that there are of order unity back-action induced spin-flip Raman scattering events within our measurement timescale. Therefore, straightforward improvements such as the use of a solid-immersion lens and higher efficiency detectors would allow for back-action evading spin measurements, without the need for a cavity

Spin entanglement using coherent light and cavity-QED

A scheme for probabilistic entanglement generation between two distant single electron doped quantum dots, each placed in a high-Q microcavity, by detecting strong coherent light which has interacted dispersively with both subsystems and experienced Faraday rotation due to the spin selective trion transitions is discussed. In order to assess the applicability of the scheme for distant entanglement generation between atomic qubits proposed by T.D. Ladd et al. [New J. Phys. 8, 184 (2006)] to two distant quantum dots, one needs to understand the limitations imposed by hyperfine interactions of the quantum dot spin with the nuclear spins of the material and by non-identical quantum dots. Feasibility is displayed by calculating the fidelity for Bell state generation analytically within an approximate framework. The fidelity is evaluated for a wide range of parameters and different pulse lengths, yielding a trade-off between signal and decoherence, as well as a set of optimal parameters. Strategies to overcome the effect of non-identical quantum dots on the fidelity are examined and the timescales imposed by the nuclear spins are discussed, showing that efficient entanglement generation is possible with distant quantum dots. In this context, effects due to light hole transitions become important and have to be included. The scheme is discussed for one- as well as for two-sided cavities, where one must be careful with reflected light which carries spin information. The validity of the approximate method is checked by a more elaborate semiclassical simulation which includes trion formation.Comment: 17 pages, 13 figures, typos corrected, reference update

Estimation of GRB detection by FiberGLAST

FiberGLAST is one of several instrument concepts being developed for possible inclusion as the primary Gamma-ray Large Area Space Telescope (GLAST) instrument. The predicted FiberGLAST effective area is more than 12,000 cm2 for energies between 30 MeV and 300 GeV, with a field of view that is essentially flat from 0°–80°. The detector will achieve a sensitivity more than 10 times that of EGRET. We present results of simulations that illustrate the sensitivity of FiberGLAST for the detection of gamma-ray bursts

The Development of Sealed UV Sensitive Gaseous Detectors and their Applications

We have developed commercial prototypes of sealed gaseous detectors combined with CsI photocathodes and/or filled with photosensitive vapors. The rirst results of application of these devices for the detection of flames in daylight conditions and for the detection of scintillation lights from noble liquids will be presented. The main conclusion from our studies is that for some applications the sealed UV sensitive gaseous detectors have superior performance (higher practical quantum efficiency and better signal to noise ratio) than existing commercial UV sensitive detectors. Additionally, they are much cheaper.Comment: Presented at the Pisa Meeting "Frontier Detectors for Frontier Physics", May 200

Measurement of the Nucleon F\u3csup\u3en\u3c/sup\u3e₂/F\u3csup\u3ep\u3c/sup\u3e₂ Structure Function Ratio by the Jefferson Lab MARATHON Tritium/Helium-3 Deep Inelastic Scattering Experiment

The ratio of the nucleon F2 structure functions, Fn2/Fp2, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from 3H and 3He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab using two high-resolution spectrometers for electron detection, and a cryogenic target system which included a low-activity tritium cell. The data analysis used a novel technique exploiting the mirror symmetry of the two nuclei, which essentially eliminates many theoretical uncertainties in the extraction of the ratio. The results, which cover the Bjorken scaling variable range 0.19 \u3c x \u3c 0.83, represent a significant improvement compared to previous SLAC and Jefferson Lab measurements for the ratio. They are compared to recent theoretical calculations and empirical determinations of the Fn2/Fp2 ratio

Development and testing of a fiber/multianode photomultiplier system for use on FiberGLAST

A scintillating fiber detector is currently being studied for the NASA Gamma-Ray Large Area Space Telescope (GLAST) mission. This detector utilizes modules composed of a thin converter sheet followed by an x, y plane of scintillating fibers to examine the shower of particles created by high energy gamma-rays interacting in the converter material. The detector is composed of a tracker with 90 such modular planes and a calorimeter with 36 planes. The two major component of this detector are the scintillating fibers and their associated photodetectors. Here we present current status of development and test result of both of these. The Hamamatsu R5900-00-M64 multianode photomultiplier tube (MAPMT) is the baseline readout device. A characterization of this device has been performed including noise, cross- talk, gain variation, vibration, and thermal/vacuum test. A prototype fiber/MAPMT system has been tested at the Center for Advanced Microstructures and Devices at Louisiana State University with a photon beam and preliminary results are presented