Laser Loop Couples Quantum Systems

A loop of laser light connects the oscillations of a nanomechanical membrane and the spin of a cloud of atoms. (Source: Dept. of Physics, U. Basel)

For the first time, researchers have succeeded in creating strong coupling between quantum systems over a greater distance. They ac­complished this with a novel method in which a laser loop connects the systems, enabling nearly lossless exchange of information and strong inter­action between them. The physicists from the Uni­versity of Basel and University of Hanover showed that the new method opens up new possi­bilities in quantum networks and quantum sensor tech­nology.

Quantum technology is currently one of the most active fields of research worldwide. It takes advantage of the special properties of quantum mechanical states of atoms, light, or nanostructures to develop, for example, novel sensors for medicine and navigation, networks for infor­mation processing and powerful simulators for materials sciences. Generating these quantum states normally requires a strong interaction between the systems involved, such as between several atoms or nano­structures. Until now, however, sufficiently strong inter­actions were limited to short distances. Typically, two systems had to be placed close to each other on the same chip at low tempera­tures or in the same vacuum chamber, where they interact via electro­static or magneto­static forces. Coupling them across larger distances, however, is required for many applications such as quantum networks or certain types of sensors.

A team of physicists, led by Philipp Treutlein from the Depart­ment of Physics at the University of Basel and the Swiss Nano­science Institute (SNI), has now succeeded for the first time in creating strong coupling between two systems over a greater distance across a room tempera­ture environment. In their experiment, the researchers used laser light to couple the vibrations of a 100 nanometer thin membrane to the motion of the spin of atoms over a distance of one meter. As a result, each vibration of the membrane sets the spin of the atoms in motion and vice versa.

The experiment is based on a concept that the researchers developed together with the theo­retical physicist Klemens Hammerer from the University of Hanover. It involves sending a beam of laser light back and forth between the systems. “The light then behaves like a mechanical spring stretched between the atoms and the membrane, and transmits forces between the two,” explains Thomas Karg, who carried out the experi­ments as part of his doctoral thesis at the Uni­versity of Basel. In this laser loop, the properties of the light can be controlled such that no infor­mation about the motion of the two systems is lost to the environ­ment, thus ensuring that the quantum mechanical inter­action is not disturbed.

The researchers have now succeeded in imple­menting this concept experi­mentally for the first time and used it in a series of experiments. “The coupling of quantum systems with light is very flexible and versatile,” explains Treutlein. “We can control the laser beam between the systems, which allows us to generate different types of inter­actions that are useful for quantum sensors, for example.”

In addition to coupling atoms with nano­mechanical membranes, the new method might also be used in several other systems; for example, when coupling super­conducting quantum bits or solid-state spin systems used in quantum computing research. The new technique for light-mediated coupling could be used to inter­connect such systems, creating quantum networks for information processing and simu­lations. Treutlein is convinced: “This is a new, highly useful tool for our quantum tech­nology toolbox.” (Source: U. Basel)

Reference: T. M. Karg et al.: Light-mediated strong coupling between a mechanical oscillator and atomic spins 1 meter apart, Science, online 7. Mai 2020; DOI: 10.1126/science.abb0328

Link: Quantum Optics Laboratory (P. Treutlein), University of Basel, Basel, Switzerland

Speak Your Mind

*