6,645 research outputs found
Detection of Fluctuating Pulsed Signals in the Presence of Noise
Control Systems Laboratory changed its name to Coordinated Science LaboratoryContract DA-36-039-SC-5669
Verifying continuous variable entanglement of intense light pulses
Three different methods have been discussed to verify continuous variable
entanglement of intense light beams. We demonstrate all three methods using the
same set--up to facilitate the comparison. The non--linearity used to generate
entanglement is the Kerr--effect in optical fibres. Due to the brightness of
the entangled pulses, standard homodyne detection is not an appropriate tool
for the verification. However, we show that by using large asymmetric
interferometers on each beam individually, two non-commuting variables can be
accessed and the presence of entanglement verified via joint measurements on
the two beams. Alternatively, we witness entanglement by combining the two
beams on a beam splitter that yields certain linear combinations of quadrature
amplitudes which suffice to prove the presence of entanglement.Comment: 11 pages, 7 figures, to appear in Phys. Rev.
Coherence of Spin Qubits in Silicon
Given the effectiveness of semiconductor devices for classical computation
one is naturally led to consider semiconductor systems for solid state quantum
information processing. Semiconductors are particularly suitable where local
control of electric fields and charge transport are required. Conventional
semiconductor electronics is built upon these capabilities and has demonstrated
scaling to large complicated arrays of interconnected devices. However, the
requirements for a quantum computer are very different from those for classical
computation, and it is not immediately obvious how best to build one in a
semiconductor. One possible approach is to use spins as qubits: of nuclei, of
electrons, or both in combination. Long qubit coherence times are a
prerequisite for quantum computing, and in this paper we will discuss
measurements of spin coherence in silicon. The results are encouraging - both
electrons bound to donors and the donor nuclei exhibit low decoherence under
the right circumstances. Doped silicon thus appears to pass the first test on
the road to a quantum computer.Comment: Submitted to J Cond Matter on Nov 15th, 200
Absolute absorption and fluorescence measurements over a dynamic range of 10 with cavity-enhanced laser-induced fluorescence
We describe a novel experimental setup that combines the advantages of both
laser-induced fluorescence and cavity ring-down techniques. The simultaneous
and correlated measurement of the ring-down and fluorescence signals yields
absolute absorption coefficients for the fluorescence measurement. The combined
measurement is conducted with the same sample in a single, pulsed laser beam.
The fluorescence measurement extends the dynamic range of a stand-alone cavity
ring-down setup from typically three to at least six orders of magnitude. The
presence of the cavity improves the quality of the signal, in particular the
signal-to-noise ratio. The methodology, dubbed cavity-enhanced laser-induced
fluorescence (CELIF), is developed and rigorously tested against the
spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density
measurements in a cell. We outline how the method can be utilised to determine
absolute quantities: absorption cross sections, sample densities and
fluorescence quantum yields.Comment: 12 pages, 6 figures, submitted to J. Chem. Phy
Sensing array for coherence analysis of modulated aquatic chemical plumes
An electrochemical sensor array can provide information about the spatial and temporal distribution of chemicals in liquid turbulent plumes. Planar laser induced fluorescence (PLIF) and amperometric sensor arrays were used to record signals from modulated chemical plumes released into a recirculating aquatic flume. Coherence analysis was applied to extract the frequency components contained in the sensor response. Effects due to release distance, modulation frequency, and array orientation were investigated. This study has demonstrated that frequency encoded information can be extracted from a turbulent chemical plume using an array of amperometric sensors with optimized three-dimensional geometry and tuning.M.S.Committee Chair: Janata, Jiri; Committee Member: Lyon, Andrew; Committee Member: Weissburg, Mar
Pump-Enhanced Continuous-Wave Magnetometry using Nitrogen-Vacancy Ensembles
Ensembles of nitrogen-vacancy centers in diamond are a highly promising
platform for high-sensitivity magnetometry, whose efficacy is often based on
efficiently generating and monitoring magnetic-field dependent infrared
fluorescence. Here we report on an increased sensing efficiency with the use of
a 532-nm resonant confocal cavity and a microwave resonator antenna for
measuring the local magnetic noise density using the intrinsic nitrogen-vacancy
concentration of a chemical-vapor deposited single-crystal diamond. We measure
a near-shot-noise-limited magnetic noise floor of 200 pT/
spanning a bandwidth up to 159 Hz, and an extracted sensitivity of
approximately 3 nT/, with further enhancement limited by the
noise floor of the lock-in amplifier and the laser damage threshold of the
optical components. Exploration of the microwave and optical pump-rate
parameter space demonstrates a linewidth-narrowing regime reached by virtue of
using the optical cavity, allowing an enhanced sensitivity to be achieved,
despite an unoptimized collection efficiency of <2 %, and a low
nitrogen-vacancy concentration of about 0.2 ppb.Comment: 10 pages and 5 figure
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