They achieve the quantum entanglement of microwave photons with photons of visible light

Quantum computers promise to solve future scientific challenges that are beyond the reach of even the most powerful conventional supercomputers. However, this will likely require millions of high-quality qubits (quantum bits) due to the necessary error correction.

Progress on superconducting processors is advancing rapidly, with current qubit counts in the hundreds. The advantages of this technology are its high computational speed and its compatibility with microchip manufacturing, but the need for ultra-cold temperatures ends up limiting the size of the processor and preventing any physical access once it has cooled down.

A modular quantum computer with multiple separately cooled processor nodes could solve this problem. However, microwave photons (the particles of light that are the native carriers of information between the superconducting qubits inside the processors) are not suitable to be sent through a room-temperature environment between the processors. Anywhere at room temperature is too hot for microwave photons and their fragile quantum properties, such as entanglement.

Researchers from the Austrian Institute of Science and Technology (ISTA), together with collaborators from the Technical University of Vienna (TU Wien) in Austria and the Technical University of Munich in Germany, have taken an important technological step to overcome these challenges.

Rishabh Sahu (ISTA) and colleagues entangled low-energy microwave photons with high-energy photons of visible light for the first time. This entangled quantum state of two photons from different bands of the electromagnetic spectrum is the basis for connections in superconducting quantum computers using room-temperature bonding.

Artist’s rendering of the experimental device with the beam of optical photons (red) entering and exiting the electro-optical crystal and resonating within its circular portion, as well as the generated microwave photons (blue) exiting the device. (Illustration: Eli Krantz / Krantz NanoArt)

The progress achieved will have implications not only for scaling existing quantum hardware, but also for interconnections with other quantum computing platforms, as well as for new applications of enhanced quantum remote sensing.

Sahu’s team exposes the details of their technical achievement in the academic journal Science, under the title “Entangling microwaves with light.” (Fountain: NCYT by Amazings)