The latest achievement by physicists with neutral atoms paves the way for new quantum computer designs.
When developing quantum computers, physicists took different paths. For example, Google recently reported that its prototype quantum computer may have performed a certain calculation faster than a classic computer. These efforts have been based on a strategy that includes superconducting materials. These materials conduct electricity without resistance when cooled to ultra-cold temperatures. Other Quantum computing Strategies involve arrays of charged or neutral atoms.
Now a team of quantum physicists at Caltech has made strides in the work that uses a more complex class of neutral atoms, the alkaline earth atoms, which are in the second column of the periodic table. These atoms, which include magnesium, calcium, and strontium, have two electrons in their outer regions or shells. Previously, researchers experimenting with neutral atoms had focused on elements in the first column of the periodic table that only have one electron in their outer shells.
In an article published in the magazine Natural physicsThe researchers show that they can use individually controlled alkaline earth atoms to achieve a characteristic of the quantum computer: entanglement. This seemingly paradoxical phenomenon occurs when two atoms remain closely connected to each other even when separated by great distances. Entanglement is essential for quantum computers, as it enables the internal “switches” of the computer, so-called qubits, to be correlated with one another and an exponential amount of information to be encoded.
“Essentially, we are breaking a two-qubit entanglement record for one of the three leading quantum science platforms: individual neutral atoms,” says Manuel Endres, assistant professor of physics and head of the Caltech team. Endres is also a member of one of three new quantum science institutes created by the National Science Foundation’s (NSF) Quantum Leap Challenges Institutes program, and a member of one of five new quantum science centers for the Department of Energy.
“We’re opening a new toolbox for quantum computers and other applications,” says Ivaylo Madjarov, a Caltech PhD student and lead author of the new study. “With alkaline earth atoms, we have more options for manipulating systems and new options for precisely manipulating and reading out the system.”
To achieve their goal, the researchers turned to optical tweezers, which are basically laser beams that can be used to maneuver individual atoms. The team previously used the same technology to come up with a new design for optical atomic clocks. In the new study, tweezers were used to entangle two strontium atoms within a row of atoms.
“We had previously shown the first control of individual alkaline earth atoms. In the present work we have added a mechanism that creates entanglement between atoms based on highly excited Rydberg states, in which atoms that are separated by many micrometers feel great forces from each other, ”says Jacob Covey, postdoctoral fellow at Caltech . “The unique properties of alkaline earth atoms offer new opportunities to improve and characterize the Rydberg interaction mechanism.”
In addition, the researchers were able to create the entangled state with a higher degree of accuracy than was previously achieved by using neutral atoms and with an accuracy comparable to other quantum computing platforms.
In the future, the researchers hope to expand their ability to control individual qubits, and they plan to further investigate methods of entangling three or more atoms.
“The endgame is to achieve a very high degree of entanglement and programmability for many atoms in order to be able to perform calculations that cannot be performed by a classic computer,” says Endres. “Our system is also suitable for examining how many –atom Entanglement could improve the stability of atomic clocks. ”
Reference: “High fidelity entanglement and detection of Rydberg alkaline earth atoms” by Ivaylo S. Madjarov, Jacob P. Covey, Adam L. Shaw, Joonhee Choi, Anant Kale, Alexandre Cooper, Hannes Pichler, Vladimir Schkolnik, Jason R. Williams and Manuel Endres, May 25, 2020, Natural physics.
DOI: 10.1038 / s41567-020-0903-z
CaltechAUTHORS: 20200312-141649005
The study published in the August issue of Natural physics was funded by NSF, the Sloan Foundation, F. Blum, Caltech, the Gordon and Betty Moore Foundation, and the Larson SURF Fellowship. Other authors at Caltech are: graduate student Adam L. Shaw; Joonhee Choi, IQIM postdoctoral fellow in physics; Anant Kale, laboratory assistant; Alexandre Cooper, former postdoctoral fellow in physics; and Hannes Pichler, former Moore Postdoctoral Scholar in Theoretical Physics; and Vladimir Schkolnik and Jason R. Williams from the Jet Propulsion Laboratory (JPL) managed by Caltech for NASA.