A team of scientists led by Prof Martin Zwierlein of MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics has built a microscope that is able to see up to 1,000 individual fermionic atoms at once.
Atoms of potassium-40 are cooled during imaging by laser light, allowing thousands of photons to be collected by the new microscope. Image credit: Lawrence Cheuk / MIT.
For the past twenty years, physicists have studied ultracold atomic gases of the two classes of particles: fermions (electrons, protons, neutrons, quarks, atoms) and bosons.
In 2009, physicists at Harvard University devised a microscope that successfully imaged individual bosons in a tightly spaced optical lattice.
The second boson microscope was created by scientists at the Max Planck Institute of Quantum Optics in Germany in 2010.
These microscopes revealed, in unprecedented detail, the behavior of bosons under strong interactions. However, no one had yet developed a comparable microscope for fermions.
The new technique developed by Prof Martin Zwierlein and his colleagues at MIT uses two laser beams trained on a cloud of fermionic atoms in an optical lattice.
The two beams, each of a different wavelength, cool the cloud, causing individual fermions to drop down an energy level, eventually bringing them to their lowest energy states – cool and stable enough to stay in place.
At the same time, each fermion releases light, which is captured by the microscope and used to image the fermion’s exact position in the lattice – to an accuracy better than the wavelength of light.
With the new technique, Prof Zwierlein’s team was able to cool and image over 95% of the fermionic atoms making up a cloud of potassium gas.
“An intriguing result from the technique appears to be that it can keep fermions cold even after imaging. That means I know where they are, and I can maybe move them around with a little tweezer to any location, and arrange them in any pattern I’d like,” said Prof Zwierlein, who is the senior author on the study published in the journal Physical Review Letters.
“High-resolution imaging of more than 1,000 fermionic atoms simultaneously would enhance our understanding of the behavior of other fermions in nature – particularly the behavior of electrons,” he said.
“This knowledge may one day advance our understanding of high-temperature superconductors, which enable lossless energy transport, as well as quantum systems such as solid-state systems or nuclear matter.”
“The group’s microscope is able to detect individual atoms with almost perfect fidelity. They detect them reliably, and do so without affecting their positions – that’s all you want,” said Prof Zoran Hadzibabic of Trinity College, who was not involved in the study.
“So far they demonstrated the technique, but we know from the experience with bosons that that’s the hardest step, and I expect the scientific results to start pouring out.”
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Lawrence W. Cheuk et al. 2015. Quantum-Gas Microscope for Fermionic Atoms. Phys. Rev. Lett., vol. 114, no. 19, 193001; doi: 10.1103/PhysRevLett.114.193001
