Experimental determination of the helium 2 3P1-1 1S0 transition rate

We present the first experimental determination of the 2 3P1–1 1S0 transition rate in helium and compare this measurement with theoretical quantum-electrodynamic predictions. The experiment exploits the very long (∼1  minute) confinement times obtained for atoms magneto-optically trapped in an apparatus used to create a Bose-Einstein condensate of metastable (2 3S1) helium. The 2 3P1–1 1S0 transition rate is measured directly from the decay rate of the cold atomic cloud following 1083 nm laser excitation from the 2 3S1 to the 2 3P1 state, and from accurate knowledge of the 2 3P1 population. The value obtained is 177±8  s-1, which agrees very well with theoretical predictions, and has an accuracy that compares favorably with measurements for the same transition in heliumlike ions higher in the isoelectronic sequence

Observation of transverse interference fringes on an atom laser beam

Using the unique detection properties offered by metastable helium atoms we have produced high resolution images of the transverse spatial profiles of an atom laser beam. We observe fringes on the beam, resulting from quantum mechanical interference between atoms that start from rest at different transverse locations within the outcoupling surface and end up at a later time with different velocities at the same transverse position. Numerical simulations in the low output-coupling limit give good quantitative agreement with our experimental data

Metastable helium: a new determination of the longest atomic excited-state lifetime

Exited atoms may relax to the ground state by radiative decay, a process which is usually very fast (of order nanoseconds). However, quantum-mechanical selection rules can prevent such rapid decay, in which case these “metastable” states can have lifetimes of order seconds or longer. In this Letter, we determine experimentally the lifetime of the longest-lived neutral atomic state—the first excited state of helium (the 2 3S1 metastable state)—to the highest accuracy yet measured. We use laser cooling and magnetic trapping to isolate a cloud of metastable helium (He*) atoms from their surrounding environment, and measure the decay rate to the ground 1 1S0 state via extreme ultraviolet (XUV) photon emission. This is the first measurement using a virtually unperturbed ensemble of isolated helium atoms, and yields a value of 7870(510) seconds, in excellent agreement with the predictions of quantum electrodynamic theory

Trap loss in a metastable helium-rubidium magneto-optical trap

We present results of the study of a simultaneously confined metastable helium (He*) and rubidium magneto-optical trap (MOT). By monitoring the trap decay of the Rb87 MOT with and without a He* MOT present, we find the light-assisted, two-body loss rate to be βRb-He*=(6±2) ×10-10 cm3/s. Moreover, we find that it is possible to create a large, robust Rb87-He* MOT, opening the possibility of creating a Rb87-He* Bose-Einstein condensate. This would be the first dual-species condensate incorporating an alkali metal ground-state atom and an excited-state noble gas atom

Active cancellation of stray magnetic fields in a Bose-Einstein condensation experiment

A method of active field cancellation is described, which greatly reduces the stray magnetic field within the trap region of a Bose-Einstein condensation experiment. An array of six single-axis magnetic sensors is used to interpolate the field at the trap center, thus avoiding the impractical requirement of placing the sensor within the trap. The system actively suppresses all frequencies from dc to approximately 3000 Hz, and the performance is superior to conventional active Helmholtz cancellation systems. A method of reducing the field gradient, by driving the six Helmholtz coils independently, is also investigated

Suppression of Penning ionization in a spin-polarized mixture of rubidium and He

This paper presents the first study of the collision dynamics of an ultra-cold spin-polarized mixture of rubidium and metastable helium (He*) atoms. Our experiment monitors ion production from the mixture for both magnetically polarized and unpolarized cases. In the unpolarized case, we observe an increase in our background ion rate. However, in the completely polarized sample the ion production is below the sensitivity of our experiment. Nonetheless, we determine an upper limit of 5 × 10-12 cm 3 s-1 for the polarized rate constant (β Rb-He*), which is two orders of magnitude below the unpolarized rate constant. Such a suppression of the He*-87Rb polarized rate was not apparent a priori and opens the intriguing possibility of creating a dual Bose-Einstein condensate comprising an alkali ground-state atom and an excited-state noblegas atom

Laser Spectroscopy of Ultracold Metastable Helium Atoms

A Bose-Einstein condensation experiment is used to create ultracold metastable helium (23S1) atoms which are probed by a 389nm laser connecting with the 33P state to study photoassociation in the short-lived molecular states thus created

Metastable Helium: Lifetime measurements using cold atoms as a test of QED

Here we present the first complete measurement of the radiative decay rate to the ground state of the lowest four triplet states of helium i.e. the metastable 23S1 state and the 23P manifold. We employ laser cooling and trapping in an ultrahigh vacuum chamber to enable direct measurement of the trap loss rate for decay from the 23P 1 state to the ground state. We then use this rate to calibrate the XUV emission decay to the ground state for all the remaining transitions. The 23P1 and 23P2 transition rates are measured for the first time, an upper bound is placed on the 23P 0 decay rate, and the 23S1 metastable lifetime is determined for only the second time with a five-fold improvement in accuracy. These results are in excellent agreement with theoretical QED predictions, and anchor the helium-like isoelectronic sequences for these transitions at low Z