We report an experiment in which an atomic excitation is localized to a spatial width that is a factor of 8 smaller than the wavelength of the incident light. The experiment utilizes the sensitivity of the dark state of electromagnetically induced transparency (EIT) to the intensity of the coupling laser beam. A standing-wave coupling laser with a sinusoidally varying intensity yields tightly confined Raman excitations during the EIT process. The excitations, located near the nodes of the intensity profile, have a width of 100 nm. The experiment is performed using ultracold 87 Rb atoms trapped in an optical dipole trap, and atomic localization is achieved with EIT pulses that are approximately 100 ns long. To probe subwavelength atom localization, we have developed a technique that can measure the width of the atomic excitations with nanometer spatial resolution.

We report temporally and spatially resolved electron property measurements of a 150 ns pulsed helium plasma jet in air operated at a low-repetition rate using Thomson laser scattering. A ringshaped electron density distribution was revealed in the pulsed plasma jet at an axial distance of 1 mm from the electrode nozzle and started to converge after 5 mm. A peak electron density of 1×10 20 m −3 was identified at the radius of the ring and close to the nozzle electrode. For a delay time ranging from 60 to 250 ns after the onset of the streamer, the electron temperature at the radius of the ring varied from 2.8 to 0.8 eV. Higher temperature >3.5 eV was also identified at regions with lower densities. Importantly, temporal development of the electron density and temperature of the plasma jet confirmed the strong dependence of guided streamer formation and propagation on the external pulsed electric field. The jet current measured during the rising and falling phases of the voltage pulse can be related to the peaks in the temporal development of the electron density.

We experimentally demonstrate the localization of excitation between hyperfine ground states of 87 Rb atoms to as small as λ/13 wide spatial regions. We use ultracold atoms trapped in a dipole trap and utilize electromagnetically induced transparency (EIT) for the atomic excitation.The localization is achieved by combining a spatially varying coupling laser (standing-wave) with the intensity dependence of EIT. The excitation is fast (150 ns laser pulses) and the dark-state fidelity can be made higher than 94% throughout the standing wave. Because the width of the localized regions is much smaller than the wavelength of the driving light, traditional optical imaging techniques cannot resolve the localized features. Therefore, to measure the excitation profile, we use an auto-correlation-like method where we perform two EIT sequences separated by a time delay, during which we move the standing wave. 1 I. 1. INTRODUCTIONThe diffraction limit, which posits that traditional optical techniques cannot resolve or write features smaller than about half the wavelength of light, is an important barrier for a variety of research areas. For example, a number of quantum computing implementations, such as those utilizing trapped neutral atoms, use focused laser beams to trap, initialize, and manipulate qubits [1][2][3][4][5]. In a neutral-atom quantum computing architecture, the qubit spacing has to be larger than half the wavelength, which limits the two-qubit interaction energies that can be obtained (for example through Rydberg dipole-dipole interaction). The necessary qubit spacing in turn limits the fidelity and the speed of the two-qubit gates. A technique to address atoms with high fidelity in sub-wavelength spatial scales would greatly improve the performance of the two-qubit gates. In this work, we use the dark state of electromagnetically induced transparency (EIT) [6][7][8][9] to address atoms in regions much smaller than the diffraction limit. We use a standing wave coupling laser and demonstrate efficient transfer between the ground levels of 87 Rb in regions with widths as small as λ/13. The transfer is fast (150 ns laser pulses) and the fidelity for the atomic system to be in the dark state can be made higher than 94% at all spatial points along the standing wave. We perform these experiments using ultracold 87 Rb atoms trapped in a far-off-resonant dipole trap at a temperature of ≈ 1 µK. Although other techniques have been investigated that achieve sub-wavelength resolution, using the dark state provides key advantages for quantum computing. The atoms are coherently transferred [9], keeping their phase relationship with other qubits intact. The dark state can be prepared with little population transfer to a radiative excited state, which reduces heating and decoherence from spontaneous emission.Because the excitation is coherent, dark-state based localization can be achieved using short and intense laser pulses, allowing fast quantum gates to be constructed.There has been other important work related to address...

This work details electron density and temperature measurements within an atmospheric nanosecond repetitively pulsed discharge in air using Thomson scattering. High voltage pulses up to 15 kV were applied to a pin-to-pin electrode configuration at several repetition frequencies to determine the effect of successive pulses on the electron parameters. Electron densities on the order of 10 17 cm −3 are measured within hundreds of nanoseconds after the discharge, with densities of 10 14 cm −3 still present in the region up to 20 μs after the initial pulse discharge. Subsequent high voltage pulses reignite the plasma, increasing the electron density from the previous pulse if the repetition frequency is above a critical value. Electron temperatures and densities were recorded at various times after the initial pulse and between subsequent pulses.

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