Strong Coupling Between Quantum Systems over Longer Distance

Scientists have used a novel method to create, for the first time, strong coupling between quantum systems over a long distance. The method involves using a laser loop to connect the systems, which enables an almost lossless exchange of strong interaction and information between them.

A loop of laser light connects the oscillations of a nanomechanical membrane (back) and the spin of a cloud of atoms (front). Image Credit: The University of Basel, Department of Physics.

Physicists at the University of Basel and University of Hanover have described in the Science journal that the new method paves way for new prospects in quantum sensor technology and quantum networks.

At present, quantum technology is one of the most active fields of studies across the globe. It leverages the unique properties of quantum mechanical states of atoms, nanostructures, or light to create, for instance, innovative sensors for navigation and medicine, robust simulators for materials sciences, and networks for information processing.

To produce such quantum states, the prerequisite is usually a strong interaction between the systems involved, for example, between multiple atoms or nanostructures.

However, to date, adequately strong interactions were restricted to shorter distances. Two systems had to be essentially placed close to one other in the same vacuum chamber or at low temperatures on the same chip. Here, they interact through magnetostatic or electrostatic forces. But it is essential to couple them over larger distances for several applications like quantum networks or sensors of specific types.

Led by Professor Philipp Treutlein from the Department of Physics at the University of Basel and the Swiss Nanoscience Institute (SNI), a group of physicists has now successfully created, for the first time, strong coupling between two systems over a larger distance in an ambient temperature environment.

As part of the experiment, laser light was used by the researchers to couple the vibrations of a 100-nm thin membrane to the motion of the atomic spin over a 1-m distance. Thus, the spin of the atoms is set in motion by each vibration of the membrane and vice versa.

A Loop of Light Acts as a Mechanical Spring

The basis for the experiment is a concept developed by the research team in collaboration with the theoretical physicist Professor Klemens Hammerer from the University of Hanover. In the concept, a beam of laser light is sent forward and backward between the systems.

The light then behaves like a mechanical spring stretched between the atoms and the membrane, and transmits forces between the two.

Dr Thomas Karg, Department of Physics, University of Basel

Dr Karg performed the experiments as part of his doctoral thesis at the University of Basel.

The properties of the light in this laser loop can be manipulated such that no information related to the motion of the two systems is lost to the environment. This ensures that the quantum mechanical interaction stays unperturbed.

Now, for the first time, the physicists have successfully performed experimental implementation of this concept and used it in a series of experiments.

The coupling of quantum systems with light is very flexible and versatile. 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.

Philipp Treutlein, Professor, Department of Physics, University of Basel

A New Tool for Quantum Technologies

Besides coupling atoms with nanomechanical membranes, the new technique could also be used in various other systems; for instance, while coupling solid-state spin systems or superconducting quantum bits used in quantum computing studies.

It would be possible to use the new method for light-mediated coupling to interconnect such systems, thus developing quantum networks for information processing and simulations.

This is a new, highly useful tool for our quantum technology toolbox.

Philipp Treutlein, Professor, Department of Physics, University of Basel

The experiments performed by the physicists in Basel were financially supported by the European Research Council as part of the project MODULAR, and by the SNI PhD School.

Journal Reference:

Karg, T. M., et al. (2020) Light-mediated strong coupling between a mechanical oscillator and atomic spins 1 meter apart. Science.


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