Modern electron microscopes achieve remarkable resolutions and can image details on the atomic scale. Yet they are not well suited for sensitive materials such as biological samples: when fragile molecules are bombarded with high-energy electron beams, such materials are quickly destroyed.
Philipp Haslinger works in the field of quantum and matter-wave optics. In recent years, his research has led him to a radically new way of extending the capabilities of electron microscopy. His idea is to use electrons as "miniature magnetic sensors" that can probe the quantum properties of a sample in a gentle, non-destructive manner, similar to the way MRI scans reveal the interior of the human body. To develop this technology further, he has now been awarded a Consolidator Grant from the European Research Council (ERC).
Electron Beams and Electron Spins
"We combine two technologies that have so far been regarded as completely separate," says Philipp Haslinger. "On the one hand electron microscopy, and on the other hand magnetic resonance spectroscopy." The two methods offer very different strengths: electron microscopy achieves nanometer-scale resolution, while magnetic resonance has lower spatial resolution but excels at distinguishing between different quantum states of matter with extraordinary sensitivity.In a conventional electron microscope, electrons essentially play the same role as light in an optical microscope: the sample is ’illuminated’ with electrons, which are then scattered and detected to create an image.
Haslinger’s team, however, takes a quantum approach. According to quantum physics, electrons behave like waves, similar to water waves reflecting from the edge of a pool and interfering with themselves. By measuring these interference patterns, one can infer how the electron interacted with the matter it passed by. "The particles in the material possess quantum spins, an intrinsic angular momentum that generates a tiny magnetic field," explains Haslinger. "We can measure this magnetic field using electrons, and we can do so a thousand times better than before."
The measurement proceeds in two steps. First, the sample is excited: microwave radiation is used to coherently manipulate the magnetic spins in a very gentle way. Then the electron beam is sent in to ’pick up’ the spin information from the sample surface."Simulations show that this technique has tremendous potential," says Haslinger. "We are very confident that in the coming years we will be able to produce extremely high-precision images with this new method."
