Stoichiometric Europium Crystal Achieves 15-Second Spin Coherence

A team from the Southern University of Science and Technology (Shenzhen), the International Quantum Academy and the Australian National University demonstrated spin coherence times of up to 15 seconds in a stoichiometric europium crystal with 100% ion concentration. Published in Physical Review Letters 137, 153601, the result removes a long-standing trade-off between optical density and coherence in quantum memory.

• Coherence up to 15 seconds in EuCl₃·6H₂O with 100% europium concentration
• Combined ZEFOZ point and CPMG sequence, each insufficient alone
• Zero-field coherence baseline improved by more than four orders of magnitude
• Matches best dilute crystals while offering far higher optical density