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First author Philip Leindecker looks into the ultrahigh-vacuum chamber of a quantum computer at PSI that operates with trapped ions. The experimental demonstration of the optical Magnus effect could contribute to controlling such quantum computers even more precisely in the future.
Photo Credit: © Paul Scherrer Institute PSI/Edgar Brucke
Scientific Frontline: Extended "At a Glance" Summary: The Optical Magnus Effect
The Core Concept: The optical Magnus effect is a physical phenomenon where the point of maximum interaction between a tightly focused laser beam and a single ion is shifted sideways from the beam's center.
Key Distinction/Mechanism: Tightly focusing a laser changes the spatial structure of its electromagnetic field, causing the interaction with the ion to be strongest slightly to one side of the center, similar to how spin changes the trajectory of a table tennis ball.
Major Frameworks/Components:
- Ion Trap: Electromagnetic fields hold a single calcium ion almost motionless.
- Calcium Ion Sensor: The electrically charged atom acts as a sensitive probe to measure shifts of just a few hundred nanometers.
- Wavelength Dependence: The magnitude of the shift relies solely on the wavelength of the light, not the tightness of the focus.
Branch of Science: Quantum Physics, Optics, Atomic Physics.
Future Application: The forces generated by this effect could be utilized to couple qubits to one another, potentially enabling more complex computations in quantum computers.
Why It Matters: In quantum computing, lasers are used to precisely control qubits; if not accounted for, the optical Magnus effect could interfere with this control and cause errors.
Researchers at the Paul Scherrer Institute (PSI), ETH Zurich, and the University of Amsterdam have directly observed the optical Magnus effect for the first time. This phenomenon is the optical counterpart of an effect from classical mechanics. It is relevant to quantum computing because it can influence the precise control of qubits, the fundamental units of quantum information.
Table tennis professionals are true masters at redirecting fast-moving projectiles. Putting a targeted spin on a serve can make the little white ball fly straight toward the edge of the table but then, at the last moment, take a sharp curve into the left corner. The physical phenomenon behind this sporting trick is known as the Magnus effect. It acts on balls of all sizes and has helped decide more than a few soccer matches.
An international research collaboration at the Paul Scherrer Institute (PSI) has now taken the leap from ball to atom, experimentally demonstrating the so-called optical Magnus effect for the first time. In this case, however, there is no atom flying along a curved trajectory. Instead, the researchers direct a tightly focused laser beam at a single ion and observe the resulting interaction.
With this, they were able to show that the point of maximum interaction is shifted sideways—an important finding for the development of quantum computers, in which laser light is used to precisely control qubits. The researchers report their findings in the journal Physical Review Letters.
When the Center Is Suddenly Off-Center
With a tightly focused laser beam directed at an ion, one would expect the strongest interaction to occur where the laser beam is most intense: at its center. However, tightly focusing the laser also changes the spatial structure of its electromagnetic field. As a result, the interaction with the ion is strongest not exactly at the center of the laser beam, but slightly to one side. This sideways shift is the optical counterpart of the Magnus effect seen in the flight of a table tennis ball.
And just as an unexpected deviation in sports can mean losing the ball, in quantum computers, it can mean the loss of control. There, laser light is used to selectively change the state of qubits. The optical Magnus effect could interfere with this precise control and contribute to errors if it is not taken into account.
At the same time, the effect also presents an opportunity: “The forces it generates could be used to couple qubits to one another, enabling more complex computations,” explains first author Philip Leindecker from the PSI Center for Photon Science and the Department of Physics at ETH Zurich.
A Map of Laser Light
To make the optical Magnus effect visible, the researchers used a single calcium ion as a tiny and extremely sensitive probe. The electrically charged atom is held almost motionless at a fixed position in a so-called ion trap using electromagnetic fields. Such trapped ions are also used in quantum computers, where they can serve as qubits whose quantum states can be precisely manipulated using laser light.
For their experiment, the researchers investigated how strongly the calcium ion interacts with the light from a tightly focused laser at different positions. “Our ion acts like a tiny sensor that we can use to feel out the structure of the laser light,” Leindecker explains. “This makes it possible to measure a shift of just a few hundred nanometers.” The experiment also revealed a surprising characteristic of the effect: the magnitude of the shift depends solely on the wavelength of the light, not on how tightly the laser is focused.
Researchers at the University of Amsterdam had theoretically predicted the optical Magnus effect several years earlier. Now, using the trapped calcium ion, the team has succeeded in observing the effect for the first time and characterizing it more precisely.
Published in journal: Physical Review Letters
Title: Direct Observation of the Optical Magnus Effect with a Trapped Ion
Authors: Philip Leindecker, Louis P. H. Gallagher, Edgar Brucke, Dominique Zehnder, Luka Milanovic, Matteo Marinelli, Rene Gerritsma, Robert J. C. Spreeuw, and Jonathan Home
Source/Credit: Paul Scherrer Institute | Benjamin A. Senn
Edited by: Scientific Frontline
Reference Number: qs082726_01
