QUIONE aims beyond merely capturing impactful images where individual atoms are discernible; its objective lies in quantum simulation.

According to researchers, quantum simulation enables us to distill highly complex systems into more manageable models, tackling unanswered questions that elude conventional computation.

The ICFO-The Institute of Photonic Sciences team’s research details were published in the journal PRX Quantum.

The use of Strontium

Quantum-gas microscopes have been shown to be effective instruments for comprehending quantum systems at the atomic level, derived from the analog quantum processors that have lately surfaced.

These gadgets enable the detection of individual atoms in the extremely high-resolution photographs of quantum gasses.

Until now, alkaline atoms such as potassium and lithium were used in these microscopy setups. These atoms have simpler optical spectrum features than alkaline-earth atoms like strontium. This indicates that strontium provides additional materials for these investigations to work with.

Due to its unique features, strontium has become particularly attractive for applications in quantum computing and quantum simulation in recent years.

An atomic quantum processor, for instance, may be created from a cloud of strontium atoms to solve issues beyond the scope of today’s classical computers.

Unlocking quantum phenomena

The team started their efforts by reducing the temperature of strontium gas in order to achieve the objective. Atoms can move very slowly or not at all by applying the force of several laser beams, which can lower their temperature to nearly absolute zero in a matter of milliseconds.

In this realm, the behaviors of atoms are governed by the laws of quantum mechanics, revealing novel characteristics such as quantum superposition and entanglement.

Subsequently, the scientists used specialized lasers to turn on the optical lattice, which maintains the atoms’ grid-like arrangement throughout space. Researchers activated the optical lattice, which keeps the atoms arranged in a grid along space.

“You can imagine it like an egg carton, where the individual sites are actually where you put the eggs. But instead of eggs we have atoms and instead of a carton we have the optical lattice,” said Sandra Buob, a researcher at ICFO and the first author of the study, in a statement.

Once the gas and optical lattice were prepared, researchers used the microscope to capture images of the strontium quantum gas, atom by atom. Although this marked the success of QUIONE’s construction, the creators sought to push its capabilities further.

Strontium gas superfluid

The team recorded videos of the atoms and noticed unexpected movements. Despite supposed stillness during imaging, atoms occasionally leaped to neighboring lattice sites, a phenomenon attributed to quantum tunneling.

Using their quantum-gas microscope, the researchers verified that the strontium gas was a superfluid—a quantum phase of matter that moves without viscosity.

 “We suddenly switched off the lattice laser so that the atoms could expand in space and interfere with each other. This generated an interference pattern due to the wave-particle duality of the atoms in the superfluid. When our equipment captured it, we verified the presence of superfluidity in the sample,” Antonio Rubio-Abadal, a researcher at ICFO, said in a statement.

With strontium included in their arsenal of quantum-gas microscopes, the researchers anticipate the potential to simulate increasingly intricate and exotic materials, thus predicting the emergence of novel phases of matter.

Furthermore, the team foresees harnessing substantially greater computational power to leverage these machines as analog quantum computers.

Abstract

The development of quantum-gas microscopes has brought novel ways of probing quantum degenerate many-body systems at the single-atom level. Until now, most of these setups have focused on alkali atoms.

Expanding quantum-gas microscopy to alkaline-earth elements will provide new tools, such as SU(N)-symmetric fermionic isotopes or ultranarrow optical transitions, to the field of quantum simulation.

Here, we demonstrate the site-resolved imaging of an 84Sr bosonic quantum gas in a Hubbard-regime optical lattice. The quantum gas is confined by a two-dimensional in-plane lattice and a light-sheet potential, which operate at the strontium clock-magic wavelength of 813.4 nm. We realize fluorescence imaging using the broad 461-nm transition, which provides high spatial resolution.

Simultaneously, we perform attractive Sisyphus cooling with the narrow 689-nm intercombination line. We reconstruct the atomic occupation from the fluorescence images, obtaining imaging fidelities above 94%.

Finally, we realize an 84Sr superfluid in the Bose-Hubbard regime. We observe its interference pattern upon expansion, a probe of phase coherence, with single-atom resolution. Our strontium quantum-gas microscope provides a new platform to study dissipative Hubbard models, quantum optics in atomic arrays, and SU(N) fermions at the microscopic level.