In a new study, Stanford researchers show how to manipulate atoms to interact with an unprecedented degree of control. Using precisely delivered light and magnetic fields, the researchers programmed a straight line of tree-shaped atoms, a twisted loop called the Möbius strip, and other patterns.
These shapes were produced not by physically moving the atoms, but by controlling how the atoms swap particles and “synchronize” to share certain properties. By carefully manipulating these interactions, researchers can generate a vast array of geometries. Importantly, they discovered that the atoms at the ends of the straight line could be programmed to interact just as strongly as the atoms located right next to each other in the center of the line. To the researchers’ knowledge, the ability to program nonlocal interactions to this degree, independent of the atoms’ actual spatial locations, had never been demonstrated before.
The findings could prove a key step in the development of advanced computing and simulation technologies based on the laws of quantum mechanics – the mathematical description of how particles move and interact at the atomic scale.
“In this paper, we demonstrated a whole new level of control over the programmability of interactions in a quantum mechanical system,” said the study’s lead author. Monika Schleier-SmithNina C. Crocker Scholar and Associate Professor at Department of Physics in Stanford School of Humanities. “This is an important step that we have been working towards for a long time, as well as being a starting point for new opportunities.”
the study published on December 22 in the magazine Nature.
Two graduate students, Avikar Periwal and Eric Cooper, as well as a postdoctoral researcher, Philipp Kunkel, are co-lead authors of the article. Periwal, Cooper and Kunkel are researchers in the Schleier-Smith lab at Stanford.
“Avikar, Eric, and Philipp worked extremely well together as a team to conduct the experiments, design clever ways to analyze and visualize the data, and develop the theoretical models,” Schleier-Smith said. “We are all very excited about these results.”
“We chose simple geometries, like rings and disconnected chains, just as a proof of principle, but we also trained more complex geometries, including ladder-like structures and tree-like interactions, which have applications for opening problems in physics,” Periwal, Cooper and Kunkel said in a group statement.
Synchronization of atoms on command
Periwal, Cooper, Kunkel and their colleagues performed experiments for the study on devices known as optical tables, a pair of which dominate the floor space in Schleier-Smith’s lab. The tables are encrusted with intricate networks of electronic components connected by multicolored wires. At the heart of an optical table is a vacuum chamber, made up of a metal cylinder studded with portholes. A pump expels all the air from this chamber so that no other atoms can disturb the small packets of rubidium atoms carefully placed inside. Stanford researchers sent lasers into this airless chamber to trap rubidium atoms, slowing the movement of the atoms and cooling them down to whiskers of absolute zero – the lowest theoretically possible temperature at which particle movement s virtually stop. The extremely cold domain just above absolute zero is where the effects of quantum mechanics can dominate those of classical physics, and therefore where atoms can be manipulated by quantum mechanics.
Shining light through the clusters of atoms in this way also serves to make the atoms “talk to each other”. When light strikes each atom, it transmits information between them, generating patterns called “correlations” in which each atom shares some desired quantum mechanical property. An example of a quantum mechanical property is the total angular momentum, known as the spin of an atom, which can have values of, for example, +1, 0 or –1.
Researchers at Stanford and elsewhere correlated atomic lattices before using laser-cooled systems of atoms, but until recently only two basic types of atomic lattices could be created. In one, called an all-to-all network, each atom communicates with all other atoms. The second type of lattice works on what is called the nearest neighbor principle, where atoms suspended in the laser interact most strongly with adjacent atoms.
In this new study, the Stanford researchers pioneer a much more dynamic method that conveys information about specific distances between discrete groups of atoms. This way the spatial location does not matter and a much richer set of correlations can be programmed.
“With a full network, it’s like I’m sending a global newsletter to everyone, whereas in a nearest neighbor network, it’s like I’m only talking to the person who lives next door” , said Schleier-Smith. . “With the programmability we’ve now demonstrated in our lab, it’s like picking up a phone and calling the exact person I want to talk to, located anywhere in the world.”
The researchers succeeded in creating these non-local interactions and correlations by controlling the frequencies of the light emitted on the trapped bunches of rubidium atoms and by varying the strength of a magnetic field applied in the optical table. As the magnetic field increased in intensity from one end of the vacuum chamber to the other, each group of atoms along the line rotated a little faster than the previous neighboring group. Although each atomic group had a unique rate of rotation, from time to time some groups nevertheless periodically arrived at the same orientation – much like how a row of clocks with hands spinning faster and faster will still read momentarily the same hours. The researchers used light to selectively activate and measure the interactions between these momentarily synchronized atomic clouds. Overall, using a straight line of 18 atom clouds, the researchers were able to generate cloud interactions at any specified set of distances along the line.
“The ability to generate and control these kinds of nonlocal interactions is powerful,” Schleier-Smith added. “It fundamentally changes the way information can travel and the quantum systems we can design.”
Boasting versatile control
One of the many applications of the Stanford team’s work is developing optimization algorithms for quantum computers – machines that rely on the laws of quantum mechanics to calculate numbers. Quantum computing has applications in artificial intelligence, machine learning, cybersecurity, financial modeling, drug development, climate change prediction, logistics, and scheduling optimization. For example, quantum algorithms tailored to computers could efficiently solve scheduling problems by finding the shortest possible routes for deliveries, or optimal scheduling of college classes so that the greatest number of students can attend.
Another very promising application is to test theories of quantum gravity. The tree shapes in this study were expressly designed for this purpose – they serve as basic models of curved spacetime by a hypothetical new concept of gravity based on principles of quantum mechanics that would reorganize our understanding of gravity such that described in Albert Einstein’s theory of relativity. . A similar approach can also be applied to study ultra-dense light-trapping cosmic objects called black holes.
Schleier-Smith and his colleagues are now working to show that their experiments can produce quantum entanglement, where quantum states between atoms are correlated in a way that can be exploited for applications ranging from ultra-precise sensors to quantum computing.
“We’ve made a lot of progress with this study and we’re looking to build on it,” Schleier-Smith said. “Our work demonstrates a new level of control that can help bridge the gap, in several areas of physics, between elegant theoretical ideas and real experiments.”
Other co-authors of the study, titled Programmable interactions and emergent geometry in a set of clouds of atomsinclude Julian F. Wienand, formerly of Stanford’s Department of Physics, now at the Ludwig-Maximilians-Universität in Munich, Germany, and Emily J. Davis of Stanford’s Department of Physics.
Funding for this research was provided by the Department of Energy’s Office of Science, Office of High Energy Physics, and Office of Basic Energy Science. Funding was also provided by the National Science Foundation, National Defense Science and Engineering Graduate Fellowship, National Science Foundation Graduate Research Fellowship Program, Hertz Foundation, and German Academic Scholarship Foundation.
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