An international team of physicists has directly observed for the first time the orbital structure of an excited hydrogen atom by building a quantum-like microscope. This device allowed them to gaze deep inside the hydrogen atom by magnifying its orbital structure to laboratory-scale dimensions.
Quantum mechanics rules the micro-scale world. The development of this theory in the early 20th century changed the way scientists understand nature. Central to this theory is the concept of wave function, which describes the probability of observing the outcome of measurements on a quantum system, such as its energy, position or momentum. Among other things, physicists can infer the atom’s orbital structure – the space in an atom that is most likely occupied by electrons – from wave functions but only by using very demanding calculations.
To date, directly observing these orbital structures was precluded since any measurement of a quantum system collapses the wave function, meaning that only one of its possible states can be measured. The latter reconciles quantum phenomena with our macroscopic view of nature but it does not help scientists to make an image of the electrons dancing around the atom’s nucleus. For capturing a full quantum state, they need a tool that can statistically average many measurements over time.
An international team of physicists, led by A. Stodolna (FOM Institute for Atomic and Molecular Physics, the Netherlands), overcame this obstacle by building a quantum-like microscope that strongly magnifies the hydrogen atom’s orbital structure so it can be visualized on a two-dimensional detector.
The observations were made using an experiment dreamed up more than 30 years ago. A beam of hydrogen atoms is placed in an electric field and excited by laser pulses. The ionized electrons can escape from the atoms along direct and indirect trajectories with respect to the detector. The phase difference between these trajectories leads to an interference pattern, which is magnified by an electrostatic lens to millimetre-scale dimensions where they could be observed on a detector. For this purpose, the team observed several hundreds of thousands of ionization events.
The interference pattern found fairly agreed with the nodal features of the hydrogen wave function, which can be calculated analytically. This demonstration establishes the microscopy technique as a fundamental tool that will help scientists better understand the mysteries of the quantum realm.
Future work is aimed on testing on how the hydrogen atom would react by the presence of a magnetic field as well as extending the study to multi-electron atoms such as helium.
For more information about the experiment, you can find the full article here.