791 research outputs found
Demonstration of an inductively coupled ring trap for cold atoms
We report the first demonstration of an inductively coupled magnetic ring trap for cold atoms. A uniform, ac magnetic field is used to induce current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap of radius 5 mm. We use a laser-cooled atomic sample to characterize the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matter-wave interferometry, offering long interaction times and large enclosed areas
Diffraction grating characterisation for cold-atom experiments
We have studied the optical properties of gratings micro-fabricated into semiconductor wafers, which can be used for simplifying cold-atom experiments. The study entailed characterisation of diffraction efficiency as a function of coating, periodicity, duty cycle and geometry using over 100 distinct gratings. The critical parameters of experimental use, such as diffraction angle and wavelength are also discussed, with an outlook to achieving optimal ultracold experimental conditions
Laser frequency stabilization to a single ion
A fundamental limit to the stability of a single-ion optical frequency
standard is set by quantum noise in the measurement of the internal state of
the ion. We discuss how the interrogation sequence and the processing of the
atomic resonance signal can be optimized in order to obtain the highest
possible stability under realistic experimental conditions. A servo algorithm
is presented that stabilizes a laser frequency to the single-ion signal and
that eliminates errors due to laser frequency drift. Numerical simulations of
the servo characteristics are compared to experimental data from a frequency
comparison of two single-ion standards based on a transition at 688 THz in
171Yb+. Experimentally, an instability sigma_y(100 s)=9*10^{-16} is obtained in
the frequency difference between both standards.Comment: 15 pages, 5 figures, submitted to J. Phys.
Parameterized bounded-depth Frege is not optimal
A general framework for parameterized proof complexity was introduced by Dantchev, Martin, and Szeider [9]. There the authors concentrate on tree-like Parameterized Resolution-a parameterized version of classical Resolution-and their gap complexity theorem implies lower bounds for that system. The main result of the present paper significantly improves upon this by showing optimal lower bounds for a parameterized version of bounded-depth Frege. More precisely, we prove that the pigeonhole principle requires proofs of size n in parameterized bounded-depth Frege, and, as a special case, in dag-like Parameterized Resolution. This answers an open question posed in [9]. In the opposite direction, we interpret a well-known technique for FPT algorithms as a DPLL procedure for Parameterized Resolution. Its generalization leads to a proof search algorithm for Parameterized Resolution that in particular shows that tree-like Parameterized Resolution allows short refutations of all parameterized contradictions given as bounded-width CNF's
A 0.8V, 7μA, rail-to-rail input/output, constant Gm operational amplifier in standard digital 0.18μm CMOS
A two-stage amplifier, operational at 0.8V and drawing 7/spl mu/A, has been integrated in a standard digital 0.18/spl mu/m CMOS process. Rail-to-rail operations at the input are enabled by complementary transistor pairs with g/sub m/ control. The efficient rail-to-rail output stage is biased in class AB. The measured DC gain of the amplifier is 75dB, and the unity-gain frequency is 870kHz with a 12pF, 100k/spl Omega/load. Both input and output stage transistors are biased in weak inversion
High-precision control of static magnetic field magnitude, orientation, and gradient using optically pumped vapour cell magnetometry
An integrated system of hardware and software allowing precise definition of arbitrarily oriented magnetic fields up to |B| = 1 μT within a five-layer Mumetal shield is described. The system is calibrated with reference to magnetic resonance observed between Zeeman states of the 6S1/2 F = 4 133Cs ground state. Magnetic field definition over the full 4π solid angle is demonstrated with one-sigma tolerances in magnitude, orientation, and gradient of δ|B| = 0.94 nT, δθ = 5.9 mrad, and δ|∇B|=13.0δ|∇B|=13.0 pT/mm, respectively. This field control is used to empirically map Mx magnetometer signal amplitude as a function of the static field (B0) orientation
Ultra-low noise, bi-polar, programmable current sources
We present the design process and implementation of fully open-source,
ultra-low noise programmable current source systems in two configurations.
Although originally designed as coil drivers for Optically Pumped Magnetometers
(OPMs), the device specifications make them potentially useful in a range of
applications. The devices feature a bi-directional current range of ~10~mA
and ~250~mA respectively on three independent channels with 16-bit
resolution. Both devices feature narrow 1/f noise bandwidth of 1~Hz, enabling
magnetic field manipulation for high-performance OPMs. They exhibit low noise
of 146.3~pA/ and 4114~pA/ which
translates to 14.57~ppb/ and 16.46~ppb/
noise relative to full scale.Comment: 9 pages, 9 figure
Design and fabrication of diffractive atom chips for laser cooling and trapping
It has recently been shown that optical reflection gratings fabricated directly into an atom chip provide a simple and effective way to trap and cool substantial clouds of atoms [1,2]. In this article we describe how the gratings are designed and micro-fabricated and we characterise their optical properties, which determine their effectiveness as a cold atom source. We use simple scalar diffraction theory to understand how the morphology of the gratings determines the power in the diffracted beams
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