The Crystal That Remembers express
Quantum memory is like a fragile snowflake: one wrong move and it melts. Scientists are hunting for materials where such a "snowflake" can be held without fear of it melting. In the new work, they studied a calcium tungstate crystal doped with erbium, a rare-earth metal. It turned out that erbium inside this crystal has a hidden property that helps hold onto information.
At temperatures below 50 millikelvin (hundreds of times colder than outer space), the scientists measured how erbium atoms respond to a magnetic field. They saw that the atoms have not only magnetic properties but also an electric field within the nucleus that had been overlooked before. It is this field that allows them to find "quiet harbors"—states where the atom barely feels external disturbances. In these states, quantum information can live much longer.
Now calcium tungstate can be considered a promising material for quantum memory. Such memory is a key to quantum computers that could communicate with each other over long distances.
Original abstract
as written by the authors arXiv:2601.16362
We report microwave spectroscopy of $$^{167}$$Er$$^{3+}$$ doped in CaWO$$_4$$ which reveals the hyperfine splitting of the erbium electronic ground state ($$Z_1$$, $$J_\mathrm{eff.}$$=15/2) induced by the $$I$$=7/2 nuclear spin. From spectra measured below$$\sim$$50 mK in magnetic fields up to 200 mT, we extract spin Hamiltonian parameters including the electron $$\textbf{g}$$, hyperfine $$\textbf{A}$$, and nuclear electric quadrupolar $$\textbf{Q}$$ tensors. Crucially, our analysis demonstrate unambiguously, that the previously unobserved nuclear electric quadrupolar moment is essential to reproduce the experimental data. With these refined parameters, we identify zero first-order Zeeman (ZEFOZ) transitions at zero magnetic field. Extending the analysis to finite fields, we uncover that ZEFOZ points lie either along the $$c$$ axis or within the $$a$$-$$b$$ plane. These results establish CaWO$$_4$$ as a promising host for long lifetime quantum memories.
Erbium is named after the Swedish village of Ytterby, where a mineral containing this element was found. The same village yielded three more elements: yttrium, terbium, and ytterbium.