A new quantum entanglement approach by Max-Planck-Institute scientists uses Brillouin scattering to link photons with acoustic phonons, enhancing stability and operating at higher temperatures.

Quantum entanglement is essential for many cutting-edge quantum technologies, including secure quantum communication and quantum computing. Researchers at the Max Planck Institute for the Science of Light (MPL) have developed an efficient new method to entangle photons with acoustic phonons. Their approach overcomes one of the most significant challenges in quantum technology—vulnerability to external noise. This groundbreaking research, published on November 13 in Physical Review Letters, opens new possibilities for robust quantum systems.

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Photons, however, are volatile. Therefore, feasible alternatives are being sought for certain applications, such as quantum memory or quantum repeater schemes. One such alternative is the acoustic domain, where quanta are stored in acoustic or sound waves.

Scientists at the MPL have now indicated a particularly efficient way in which photons can be entangled with acoustic phonons: While the two quanta travel along the same photonic structures, the phonons move at a much slower speed. The underlying effect is the optical nonlinear effect known as Brillouin-Mandelstam scattering. It is responsible for coupling quanta at fundamentally different energy scales.

In their study, the scientists showed that the proposed entangling scheme can operate at temperatures in the tens of Kelvin. This is much higher than those required by standard approaches, which often employ expensive equipment such as dilution fridges. The possibility of implementing this concept in optical fibers or photonic integrated chips makes this mechanism of particular interest for use in modern quantum technologies.