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Journal of the Optical Society of America B

Performance of a feedback-controlled, deterministic source of single chromium atoms

Shannon B. Hill, Jabez J. McClelland

Published Mar 1, 2004• 4 citations
Publisher

Abstract

A magneto-optical trap with feedback-controlled loading and loss rates is used to realize a deterministic source of single chromium atoms with single-atom occupation probability as high as 0.987±0.001. We present a series of measurements of the performance of this source and discuss the dependence of the probability of not having a single atom in the trap (error rate) on experimental parameters. We describe a simple analytical model that considers mean load rate, trap lifetime, stray load rate, and feedback response time, and we also present results of Monte Carlo calculations that take into account all experimental conditions. We find that the analytical model describes the behavior well for error rates as small as about 0.03, but the Monte Carlo simulations must be used to model behavior at error rates lower than this, as the occupation probability approaches unity.

DOI
10.1364/josab.21.000473

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A magneto-optical trap with feedback-controlled loading and loss rates is used to realize a deterministic source of single chromium atoms with single-atom occupation probability as high as 0.987±0.001. We present a series of measurements of the performance of this source and discuss the dependence of the probability of not having a single atom in the trap (error rate) on experimental parameters. We describe a simple analytical model that considers mean load rate, trap lifetime, stray load rate, and feedback response time, and we also present results of Monte Carlo calculations that take into account all experimental conditions. We find that the analytical model describes the behavior well for error rates as small as about 0.03, but the Monte Carlo simulations must be used to model behavior at error rates lower than this, as the occupation probability approaches unity.
We have realized a method for producing single Cr atoms on demand by suppressing the stochastic nature of the loading and loss processes of a magneto-optic trap. We observe single-atom trap occupation probabilities as high as (98.7±0.1)% and demonstrate ejection with greater than 90% efficiency at rates up to 10 Hz. Monte Carlo simulations agree well with extraction measurements and are used to predict ultimate performance. Such a deterministic atom source has potential applications in nanotechnology, quantum information processing, and fundamental quantum investigations.
Based on feedback control techniques and our realization of nearly complete transferring cold cesium (Cs) atoms from a magneto-optical trap (MOT) to a far-off-resonance microscopic optical tweezer, we investigated the possibility for nearly deterministic loading of a single Cs atom in a MOT and in a microscopic optical tweezer. We combined feedback controls on the gradient of the MOT quadrupole magnetic field (QMF) and on blue-detuned light-assisted collisions (LAC) of confined cold atoms in the tweezer. Using active feedback on QMF of the MOT, we have achieved ~ 98% of probability of single atom loading in a MOT. In a microscopic optical tweezer, by combining the feedback controls on the QMF and the LAC, we finally achieved ~ 95.2% of probability of single atom loading in the tweezer. This two-path feedback control scheme may be extended to load a small-size 2D tweezer array with exact single atom trapped in each site simultaneously. This is very important and promising to implement an addressable multiple-qubit system for demonstrating quantum register and quantum processor.
A quantitative study on characteristics of a magneto-optical trap with a single or a few atoms is presented. A very small number of 85 Rb atoms were trapped in a micron-size magneto-optical trap with a high magnetic-field gradient. In order to find the optimum condition for a single-atom trap, we have investigated how the number of atoms and the size of atomic cloud change as various experimental parameters, such as a magnetic-field gradient and the trapping laser intensity and detuning. The averaged number of atoms was measured very accurately with a calibration procedure based on the single-atom saturation curve of resonance fluorescence. In addition, the number of atoms in a trap could be controlled by suppressing stochastic loading events by means of a real-time active feedback on the magnetic-field gradient.
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In this article a Markov chain for the distribution of single atoms is suggested and studied. We explore a recursive model for the number of atoms present in a magneto-optical trap under a feedback regime with a Poisson-distributed load. Formulas for the stationary distribution of this process are derived. They can be used to adjust the loading rate of atoms to maximize the proportion of time that a single atom spends in the trap. The (approximate) optimal regime for the Poisson loading and loss processes is found.