Spin Rephasing Stores Single Photons for 180 Microseconds
ICFO researchers stored single photons for up to 180 microseconds using spin rephasing in a praseodymium-doped crystal quantum memory, advancing the
Researchers at ICFO-The Institute of Photonic Sciences in Barcelona have stored single photons for up to 180 microseconds using a spin-rephased solid-state quantum memory. The study, titled 'Long-lived storage of single photons in a spin-rephased solid-state quantum memory', used a praseodymium-doped crystal cooled to 3 kelvin inside a cryostat.
Method enables quantum light storage via spin rephasing
The team used the Atomic Frequency Comb protocol to store entangled photons. They generated a pair: one photon at a telecom wavelength and one matched to the crystal's absorption profile. An optical control pulse transferred the collective excitation into the spin state of the ions to pause re-emission. A later pulse triggered the photon's release.
To counteract dephasing caused by the varying local environments of ions in the crystal, the researchers applied a train of radiofrequency pulses at carefully chosen intervals. This spin rephasing technique flips and compensates for accumulated phase. Hugues de Riedmatten, an ICREA professor who led the research, noted the significance of applying this method to quantum light. "Spin rephasing had been demonstrated in the past with classical input states, but our results show that it can be extended to quantum light," he said.
Storage corresponds to long-distance quantum link potential
The 180-microsecond storage time is functionally equivalent to a photon traveling through an optical fiber for more than 30 kilometers. In the experiment, the detection of the telecom photon acted as a herald, certifying the delivery of its entangled partner-a single photon-into the memory. The quantum correlations between the stored photon and the telecom herald photon survived the entire storage and retrieval process.
Path forward for scalable quantum networks
The work was carried out within the Quantum Internet Alliance project. It establishes praseodymium-doped crystals as a leading candidate for building quantum repeaters, which are essential for scaling quantum networks over continental distances. Researcher Alberto RodrÃguez Moldes pointed to a clear path for improvement. "In the future, longer storage times will be available by applying small magnetic fields to the quantum memory," he said.
Applying small magnetic fields could enable longer storage times.
