Active stabilization of ion trap radiofrequency potentials
Disclosed are improved methods and structures for actively stabilizing the oscillation frequency of a trapped ion by noninvasively sampling and rectifying the high voltage RF potential at circuit locations between a step-up transformer and a vacuum feedthrough leading to the ion trap electrodes. We use this sampled/rectified signal in a feedback loop to regulate the RF input amplitude to the circuit. By employing techniques and structures according to the present disclosure we are advantageously able to stabilize a 1 MHz trapped ion oscillation frequency to <10 Hz after 200 s of integration, representing a 34 dB reduction in the level of trap frequency noise and drift, over a locking bandwidth of up to 30 kHz.
1. A method for actively stabilizing ion trap radiofrequency (RF) potentials comprising:
noninvasively sampling a high voltage potential at a position in a circuit between a step-up transformer and a vacuum feedthrough for electrodes of the ion trap;
rectifying the sampled high voltage potential signal;
applying the rectified signal to a frequency mixer that controls an RF oscillator amplitude;
generating an error signal by comparing the rectified signal to a stable set-point voltage reference;
amplifying the error signal and then applying the error signal to the frequency mixer; and
applying the rectified signal to a feedback loop of the circuit such that an amplitude of an RF input to the circuit is desirably regulated and the ion trap RF potentials are actively stabilized;
wherein the rectification is performed through the effect of a temperature compensating rectifier including two matched diodes configured for passive temperature compensation in conjunction with a low-pass filter configured such that a ripple amplitude of at least 10dB below diode input signal amplitude is produced.
2. The method according to claim 1 further comprising stabilizing a ratio of voltage to frequency (V 0 /Ω) through the effect of a digital counter and divider circuit.
3. The method according to claim 2 wherein the ion trap is a component of a system selected from the group consisting of: quantum information processor, ion trap mass spectrometer, and multipole mass spectrometer.
4. The method according to claim 3 wherein the ion trap exhibits a geometry selected from the group consisting of: quadrupole trap, linear trap, surface ion trap, hexapole trap, and higher-order trap.
5. The method according to claim 4 wherein the sampling and providing are effected under the control of a digital computer.
6. A system for actively stabilizing ion trap radiofrequency (RF) potentials comprising:
means for noninvasively sampling a high voltage potential at a position in a circuit between a step-up transformer and a vacuum feedthrough for electrodes of the ion trap;
means for rectifying the sampled high voltage potential signal;
means for applying the rectified signal to a feedback loop of the circuit such that an amplitude of an RF input to the circuit is desirably regulated. and the ion trap RF potentials are actively stabilized;
means for applying the rectified signal to a frequency mixer that controls an RF oscillator amplitude;
means for generating an error signal by comparing the rectified signal to a stable set-point voltage reference; and
means for amplifying the error signal and then applying the error signal to the frequency mixer;
wherein the rectifying means further includes temperature compensating means including two matched diodes configured for passive temperature compensation in conjunction with a low-pass filter configured such that a ripple amplitude of at least 10dB below diode input signal amplitude is produced.
7. The system according to claim 6 further comprising a voltage to frequency (V 0 /Ω) stabilizing means.