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H Dehmelt

Publications and source records attributed to H Dehmelt.

25 records · Page 2Linked to original sources
PubMed1986

Continuous Stern-Gerlach effect: Noise and the measurement process.

This paper resumes the discussion of the continuous Stern-Gerlach effect, a method to continuously and nondestructively determine the spin state of the same individual electron, quasipermanently confined in a Penning trap in ultrahigh vacuum at liquid helium temperatures. Here the focus is on limitations to spin-state detection due to thermal and zero-point noise and on the quantum-mechanical measurement process. Illustrations of the continuous spin measurement process in the presence of selected perturbations are provided. The alteration of the spin state brought about by the frequency measurement process is exhibited. To resolve Zeno's paradox in a specific example, a slow resonant spin flip is discussed, when interrupted by frequent spin-state measurements. The continuous Stern-Gerlach effect is shown to be a near-ideal example for the quantum mechanical measurement process, for which all steps may be followed in quantitative detail.

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PubMed1986

Self-excited mono-ion oscillator.

We propose self-excitation as a potentially more sensitive technique for studying a mono-ion oscillator of frequency v(z) approximately 0.1-100 MHz. This technique also makes only low demands on the harmonicity of the ion oscillation. It should therefore work with inexpensive, easily constructed rf traps. In our analysis, the bound ion between the trap electrodes is represented by an effective circuit resembling that of a piezoelectric quartz crystal. The feedback circuit developed, when operated below self-excitation threshold, may also make efficient electronic cooling of the ion possible, particularly in conjunction with a heterodyne feedback scheme. In the super-regenerative mode, the apparatus might function as a powerful atomic amplifier of the ion oscillation for an energy as low as a fraction of hv(z). These techniques may prove especially useful in conjunction with attempts to synthesize in an rf trap a loosely bound anti-hydrogen atom from a positron and antiproton.

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PubMed1986

Continuous Stern-Gerlach effect: Principle and idealized apparatus.

A nondestructive type of Stern-Gerlach effect for an individual electron is described that has been thoroughly demonstrated in experiments at the University of Washington. This "continuous Stern-Gerlach effect" makes use of an inhomogeneous magnetic field provided by a weak auxiliary magnetic bottle and is nondestructive in contrast to all previous versions of the effect. As in the classic Stern-Gerlach effect, changes in the spin state are detected via changes in classical particle trajectories; however, what is observed now is not a deflection of the orbit but rather a change of its frequency in the storage well. A simplified model of the continuous Stern-Gerlach effect at zero temperature is introduced to develop the relation between minimum measurement time required for determination of spin state, driven oscillation amplitude, and zero-point fluctuations in the storage well. The problem of the reduction of the wavefunction by the interaction of the electron with the apparatus is addressed following W. Pauli.

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PubMed1984

g-Factor of electron centered in symmetric cavity.

The cyclotron frequency of an electron localized in the center of a cylindrical microwave cavity differs slightly from that in free space. To see this, the system is modeled by a series resonant lc circuit for the cyclotron motion connected across the center of a section of two-wire transmission line (the cavity). When the transmission line is infinitely long, its input impedance at terminals in its center is strictly ohmic and equal to half its characteristic impedance. This ohmic impedance completes the lc circuit, essentially without changing its resonant frequency but damping it. This is the analog of the cyclotron motion in free space that is damped by spontaneous emission. Free space may be mimicked by a short section of transmission line that is terminated at both ends by resistors equal in value to its characteristic impedance. A slightly lossy cavity is modeled by a section of line terminated by resistors much smaller than the characteristic impedance. When the frequency of the lc circuit/cyclotron motion is chosen thus that the line/cavity contains exactly an even number of half-waves, its input impedance will be ohmic and much smaller than its characteristic impedance. Therefore, the frequency of the lc circuit/cyclotron motion will be the same as in vacuum but spontaneous emission and associated line broadening will be much reduced. The g-factor of the electron measured under these conditions practically equals the free space value. This follows because g is determined by the ratio of spin and cyclotron frequencies and the spin practically does not couple to the radiation field.

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PubMed1983

Linewidth of single laser-cooled Mg ion in radiofrequency trap.

A single Mg(+) has been successfully trapped and cooled in a small radiofrequency trap. The ion was cooled by using the radiation from a single-frequency ring dye laser whose output was doubled in frequency with an NH(4) (2)H(2)PO(4) temperature phasematched crystal; a power of about 22 muW or less was sufficient for all of the experiments. The ion temperature was estimated by a computer fit of the experimental resonance line profile; the resulting linewidth was compared to previously published Mg(+) 3(2)P(3/2) Hanle-effect linewidths. The result is a temperature of 5(-5) (+15) mK, which is lower than that attained previously.

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