Trapped Antihydrogen in Its Ground State

Antihydrogen atoms ($\overline{\mathrm{H}}$) are confined in an Ioffe trap for 15–1000 s—long enough to ensure that they reach their ground state. Though reproducibility challenges remain in making large numbers of cold antiprotons ($\overline{p}$) and positrons ($e^{+}$) interact, $5\pm 1$ simultaneously confined ground-state atoms are produced and observed on average, substantially more than previously reported. Increases in the number of simultaneously trapped $\overline{\mathrm{H}}$ are critical if laser cooling of trapped $\overline{\mathrm{H}}$ is to be demonstrated and spectroscopic studies at interesting levels of precision are to be carried out.

Figure 1

Electrodes and coils produce Penning traps (to store $\overline{p}$ and $e^{+}$) and an Ioffe trap [22] (to store $\overline{\mathrm{H}}$). Much of the vacuum enclosure and cooling system is hidden to make the traps and detectors visible. An external solenoid (not shown) adds a 1 T magnetic field along the trap axis $\widehat{\mathbf{z}}$ which is vertical.

Figure 2

(a) Potentials along the center axis used to contain (solid line) and remove (dashed line) charged particles. (b) Electrode cross sections with equipotential energy contours for a low-field-seeking, ground state $\overline{\mathrm{H}}$ in the Ioffe trap. (c) Axial electric field contours used to clear $\overline{p}$ and $e^{+}$ before trapped $\overline{\mathrm{H}}$ are detected. The trap axis is vertical.

Figure 3

(a) The emf induced across the field-boosting solenoid as the Ioffe racetrack coil quenches. (b) Deduced Ioffe trap well depth for ground state $\overline{\mathrm{H}}$ shows that if these fill the trap uniformly in energy 93% will escape within 1 s after the quench.

Figure 4

(a) Detector counts in 1 s intervals for 20 trials. The radial Ioffe trap field turns off and releases trapped $\overline{\mathrm{H}}$ between $t=0$ and 1 s. The counts in this interval above the average cosmic ray counts (solid line) correspond to 105 trapped $\overline{p}$ for our detection efficiency. (b) Probability that cosmic rays produce the observed counts or more. (c) Quenching the Ioffe trap generates no false signals in 20 control trials.