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Manuel Endres, an educator in physics at Caltech, focuses on meticulously managing single atoms utilizing apparatuses referred to as optical tweezers. He and his team employ these tweezers, constructed from laser light, to manipulate solitary atoms within an atomic array to investigate essential characteristics of quantum systems. Their research has resulted in, among various breakthroughs, innovative methods for eliminating errors in basic quantum machines; a novel device that might lead to the most accurate clocks in the world; and a record-setting quantum system manipulating over 6,000 distinct atoms.
One persistent challenge in this area of study has been the typical wiggling motion of atoms, which complicates the control of the systems. Now, as reported in the journal Science, the research group has turned this issue into an advantage by utilizing this atomic motion to encode quantum information, a property fundamental to quantum technologies.
“We demonstrate that atomic motion, usually regarded as a source of undesirable noise in quantum systems, can be transformed into an asset,” remarks Adam Shaw (PhD ’24), a co-lead author of the research alongside Pascal Scholl and Ran Finkelstein. Shaw was previously a graduate scholar at Caltech during these investigations and is currently a postdoctoral researcher at Stanford University. Scholl worked as a postdoc at Caltech and is presently employed at the quantum computing firm Pasqal. Finkelstein was awarded the Troesh Postdoctoral Prize Fellowship at Caltech and is now a faculty member at Tel Aviv University.
Ultimately, the experiment not only encoded quantum information in the atomic motion but also resulted in a state referred to as hyper-entanglement. In simple entanglement, two particles remain linked despite being separated by enormous distances. When scientists observe the states of the particles, they notice this correlation: For instance, if one particle is in a state known as spin up (where the angular momentum is oriented upwards), the other will invariably be in spin down.
In hyper-entanglement, two attributes of a pair of particles are interconnected. As a simple metaphor, this resembles twins separated at birth sharing both the same names and identical types of vehicles: The two characteristics are correlated between the twins. In the recent study, Endres and his team managed to hyper-entangle pairs of atoms so that their individual motion states and their individual electronic states—their internal energy levels—were correlated among the atoms. Furthermore, this experimental demonstration suggests that even more attributes could be entangled simultaneously.
“This enables us to encode a greater amount of quantum information per atom,” Endres clarifies. “You achieve more entanglement with fewer resources.”
This experiment represents the inaugural demonstration of hyper-entanglement in massive particles, such as neutral atoms or ions (previous demonstrations involved photons).
For these investigations, the team cooled an array of individual neutral alkaline-earth atoms confined within optical tweezers. They showcased a novel form of cooling through “detection and subsequent active correction of thermal motional excitations,” explains Endres, comparing it to James Clerk Maxwell’s well-known 1867 thought experiment involving a demon that measures and sorts particles in a chamber. “We effectively monitor the motion of each atom and apply an operation based on the results, atom-by-atom, resembling Maxwell’s demon.”
This approach, which surpassed the most effective laser cooling techniques, caused the atoms to nearly halt in motion.
Following this, the researchers encouraged the atoms to oscillate like a pendulum, but with an amplitude of approximately 100 nanometers, which is considerably smaller than the width of a human hair. They managed to excite the atoms into two distinct oscillations simultaneously, placing the motion in a state of superposition. Superposition is a quantum state wherein a particle displays contradictory traits at the same time, such as a particle’s spin being both up and down concurrently.
“You can envision an atom moving in this state of superposition akin to a child on a swing being pushed by two parents from opposite sides concurrently,” Endres observes. “In our everyday lives, this would undoubtedly lead to a parental dispute; in the quantum realm, we can astonishingly harness this!”
They subsequently entangled the individual, oscillating atoms into paired atoms, establishing a correlated state of motion over several micrometers of distance. After entangling the atoms, the team then hyper-entangled them in such a manner that both their motion and electronic states became correlated.
“Essentially, the objective here was to extend the limits of how effectively we could control these atoms,” Endres remarks. “We are fundamentally constructing a toolkit: We previously knew how to manage the electrons within an atom, and now we have learned to regulate the overall external motion of the atom. It’s like mastering an atomic toy.”
These findings could pave the way for innovative methods of conducting quantum computing as well as quantum simulations aimed at exploring fundamental inquiries in physics. “Motional states could evolve into a significant resource for quantum technology, spanning computing, simulation, and precision measurements,” Endres states.
The latest study titled “Erasure cooling, control, and hyperentanglement of motion in optical tweezers,” received funding from the Army Research Office, the National Science Foundation’s (NSF’s) Quantum Leap Challenge Institute, the Institute for Quantum Information and Matter at Caltech (an NSF Physics Frontiers Center), the U.S. Defense Advanced Research Projects Agency, the U.S. Department of Energy’s Quantum Systems Accelerator, an NSF CAREER (Faculty Early Career Development Program) award, the Troesch postdoctoral fellowship, and the Taiwan-Caltech Fellowship. Additional authors include Caltech graduate student Richard Bing-Shiun Tsai and former Caltech postdoc Joonhee Choi.
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