Scientists develop device to convert quantum information between microwave and optical photons

Researchers at the QOT Centre for Quantum Optical Technologies, in collaboration with a student from the Faculty of Physics at the University of Warsaw, have developed a groundbreaking device. This invention has the remarkable capability to seamlessly convert quantum information between microwave and optical photons.

Their groundbreaking findings, which have been published in the prestigious journal Nature Photonics, shed light on an innovative microwave detection technique. This method holds immense promise for various applications within the realm of quantum technologies, serving as an integral component of quantum network infrastructure. Additionally, it has the potential to significantly advance the field of microwave radio-astronomy.

Conversion of quantum information

Each time you enjoy a song on your electronic device, a remarkable transformation takes place. It involves the conversion of a digitally encoded file stored in your device’s memory into an electric current that powers your headphones. In a similar vein, the world of quantum information sees an equally fascinating conversion process, one that revolves around encoding information in the tiniest units of light, photons.

Imagine the ability to transfer information from a solitary microwave photon to a lone optical photon. While this may sound like science fiction, it’s a challenging endeavor in reality. Achieving this requires precision and minimal noise, making the creation of such single-photon devices a formidable task. What adds to the complexity is that optical photons possess energy levels tens of thousands of times greater than their microwave counterparts, and only a handful of mediums can interact with both types simultaneously.

However, this challenge holds immense significance for the development of hybrid quantum networks. These networks aim to connect various quantum devices, including quantum computers. Quantum computing often involves microwave photons interacting with superconducting circuits, but transmitting quantum information over long distances in this manner faces hurdles due to noise accumulation.

The game-changer here is the role of optical photons. They excel at efficiently transmitting quantum information through optical fibers, eliminating the noise accumulation issue. Thus, a microwave-to-optical quantum information converter emerges as a vital component—a quantum network adapter that bridges the gap between quantum computers and the emerging quantum internet.

Enlarged atoms

In the realm of quantum physics, there exists a fascinating medium capable of interacting with both microwave and optical photons: Rydberg atoms, a tribute to Johannes Rydberg’s pioneering work in optical spectroscopy during the 19th century, where he unveiled the famous Rydberg formula. These Rydberg atoms are crafted through laser excitation of valence electrons, often found within rubidium atoms.

When subjected to this laser-induced metamorphosis, these atoms undergo a remarkable transformation, expanding in size by a factor of a thousand while manifesting an array of intriguing properties. This captivating field of study has become a focal point of scientific research worldwide. Notably, Rydberg atoms exhibit exceptional sensitivity to microwave radiation.

Until now, the phenomenon of converting microwave signals to optical ones has primarily been witnessed within the confines of meticulously controlled laser-cooled atoms, ensnared within complex magneto-optical trapping setups. However, researchers at the University of Warsaw have achieved a groundbreaking milestone by demonstrating that microwave-to-optical conversion can occur at room temperature, within atomic vapors confined within a humble glass cell.

What sets their proposed converter apart is its remarkable simplicity and the potential for future miniaturization. Moreover, this novel conversion scheme boasts remarkably low noise levels, enabling it to operate effectively even with single photons. Astonishingly, this simplified setup surpasses its predecessors in terms of performance parameters.

Most notably, the innovation birthed at the University of Warsaw operates continuously, eliminating the need for specially designed time sequences that often consume more than 99% of operational time in experiments conducted by other research groups.

With this converter device, the scientists at UW have achieved a significant milestone: the detection of microwave thermal radiation at room temperature—marking a historic first without the need for microwave antennas or specialized low-noise amplifiers. To reach thermal sensitivity levels, the device must be attuned to single photons. Nevertheless, the converter can withstand microwave radiation a million times stronger and remains impervious to even more potent fields, distinguishing it from conventional microwave devices.

The future lies in microwaves

In the realm of rapidly advancing quantum technologies, diverse information carriers come into play. Quantum computers, reliant on superconducting junctions, encode their data in the realm of microwave frequencies. In contrast, quantum memories predominantly rely on the manipulation of optical photons. Just as the quantum network adapter seeks to bridge these two distinct device types, there arises a pressing need for an interface that can seamlessly operate across both microwave and optical domains. Enter Rydberg atoms, presenting a promising solution to this conundrum.

The significance of single-photon microwave operations extends far beyond the confines of the lab. These operations hold the key to unraveling mysteries in the cosmos, enabling astronomical observations that delve into the properties of distant celestial bodies and unveil the early universe’s shape through precise measurements of the cosmic microwave background. Historically, retaining quantum information within microwave photons has remained an elusive goal. The advent of microwave-to-optical conversion could potentially give rise to an entirely new branch of microwave radio-astronomy.

But the applications of these breakthroughs aren’t limited to the stars; they permeate our everyday lives as well. The future of mass communication hinges on next-generation mobile technologies, poised to leverage high-frequency microwave transmission bands that conventional electrical circuits find challenging to emit and detect. One can envision a future where atomic microwave sensors play a pivotal role in delivering lightning-fast internet connections.

This vision drives ongoing research not only at the Centre for Quantum Optical Technologies (QOT) but also in scientific institutes worldwide. The goal is clear: to harness the power of quantum technologies in the realm of ultrasensitive microwave detection, unlocking new frontiers in our understanding of the universe and revolutionizing how we connect and communicate.

Source: University of Warsaw

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