Laser cooling traps more antimatter atoms than ever before

M. Hori

Benjamin A. Thompson, Nick Petrić Howe

C. J. Baker, William Alan Bertsche, A. Capra +55 more

Abstract The photon—the quantum excitation of the electromagnetic field—is massless but carries momentum. A photon can therefore exert a force on an object upon collision1. Slowing the translational motion of atoms and ions by application of such a force2,3, known as laser cooling, was first demonstrated 40 years ago4,5. It revolutionized atomic physics over the following decades6–8, and it is now a workhorse in many fields, including studies on quantum degenerate gases, quantum information, atomic clocks and tests of fundamental physics. However, this technique has not yet been applied to antimatter. Here we demonstrate laser cooling of antihydrogen9, the antimatter atom consisting of an antiproton and a positron. By exciting the 1S–2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-α laser radiation10,11, we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions. We observe a reduction in the median transverse energy by more than an order of magnitude—with a substantial fraction of the anti-atoms attaining submicroelectronvolt transverse kinetic energies. We also report the observation of the laser-driven 1S–2S transition in samples of laser-cooled antihydrogen atoms. The observed spectral line is approximately four times narrower than that obtained without laser cooling. The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic11–13 and gravitational14 studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.

Shin Satori, Hitoshi Kuninaka, K. Kuriki

The storage of antimatter in an electrically neutral state is one of the breakthroughs required to realize antimatter applications. In this work, use of laser cooling to manipulate the motion of neutral atoms by radiative pressure was demonstrated using a commercial laser diode and metastable argon as antimatter simulant. The concept of critical velocity was introduced as a criterion for the laser cooling and its importance was experimentally demonstrated.

Philip H. Jones, Onofrio M. Maragò, Giovanni Volpe

J. Walz

We discuss laser cooling of antihydrogen atoms in a magnetic trap down to the millikelvin range using radiation at Lyman‐alpha. This is very important to suppress residual Zeeman shifts and broadenings in future high‐resolution laser‐spectroscopy of antihydrogen. Even colder antihydrogen temperatures in the sub‐millikelvin range are desirable for experiments on antimatter gravity. We discuss novel methods to obtain antihydrogen atoms at these ultracold temperatures.