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Researchers have discovered a way to translate quantum information between different kinds of quantum technologies, with significant implications for quantum computing, communication, and networking.

The research, published in the journal Nature, was funded by the Army Research Office (ARO), the Air Force Office of Scientific Research (AFOSR), and the NSF Quantum Leap Challenge Institute for Hybrid Quantum Architectures and Networks (HQAN), which is led by the University of Illinois Urbana-Champaign. It represents a new way to convert quantum information from the format used by quantum computers to the format needed for quantum communication.

Photonsparticles of lightare essential for quantum information technologies, but different technologies use them at different frequencies. For example, some of the most common quantum computing technology is based on superconducting qubits, such as those used by tech giants Google and IBM; these qubits store quantum information in photons that move at microwave frequencies.

But if you want to build a quantum network, or connect quantum computers, you cant send around microwave photons because their grip on their quantum information is too weak to survive the trip.

A lot of the technologies that we use for classical communicationcell phones, Wi-Fi, GPS, and things like thatall use microwave frequencies of light, said Aishwarya Kumar, a postdoc at the James Franck Institute at University of Chicago and lead author on the paper. But you cant do that for quantum communication because the quantum information you need is in a single photon. And at microwave frequencies, that information will get buried in thermal noise.

The solution is to transfer the quantum information to a higher-frequency photon, called an optical photon, which is much more resilient against ambient noise. But the information cant be transferred directly from photon to photon; instead, we need intermediary matter. Some experiments design solid state devices for this purpose, but Kumars experiment aimed for something more fundamental: atoms.

The electrons in atoms are only ever allowed to have certain specific amounts of energy, called energy levels. If an electron is sitting at a lower energy level, it can be excited to a higher energy level by hitting it with a photon whose energy exactly matches the difference between the higher and lower level. Similarly, when an electron is forced to drop to a lower energy level, the atom then emits a photon with an energy that matches the energy difference between levels.

Rubidium atoms happen to have two gaps in their levels that Kumars technology exploits: one that exactly equals the energy of a microwave photon, and one that exactly equals the energy of an optical photon. By using lasers to shift the atoms electron energies up and down, the technology allows the atom to absorb a microwave photon with quantum information and then emit an optical photon with that quantum information. This translation between different modes of quantum information is called transduction.

Effectively using atoms for this purpose is made possible by the significant progress scientists have made in manipulating such small objects. We as a community have built remarkable technology in the last 20 or 30 years that lets us control essentially everything about the atoms, Kumar said. So the experiment is very controlled and efficient.

He says the other secret to their success is the fields progress in cavity quantum electrodynamics, where a photon is trapped in a superconducting, reflective chamber. Forcing the photon to bounce around in an enclosed space, the superconducting cavity strengthens the interaction between the photon and whatever matter is placed inside it.

Their chamber doesnt look very enclosedin fact, it more closely resembles a block of Swiss cheese. But what look like holes are actually tunnels that intersect in a very specific geometry, so that photons or atoms can be trapped at an intersection. Its a clever design that also allows researchers access to the chamber so they can inject the atoms and the photons.

The technology works both ways: it can transfer quantum information from microwave photons to optical photons, and vice versa. So it can be on either side of a long-distance connection between two superconducting qubit quantum computers, and serve as a fundamental building block to a quantum internet.

But Kumar thinks there may be a lot more applications for this technology than just quantum networking. Its core ability is to strongly entangle atoms and photonsan essential, and difficult task in many different quantum technologies across the field.

One of the things that we're really excited about is the ability of this platform to generate really efficient entanglement, he said. Entanglement is central to almost everything quantum that we care about, from computing to simulations to metrology and atomic clocks. Im excited to see what else we can do.

- This press release was originally published on the Chicago Quantum Exchange website

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New Experiment Translates Quantum Information between ... - Lab Manager Magazine