**The element of success**

Atomic Dysprosium $(Z=66)$ has a ground-state configuration of $4f^{10} 6s^2$ and a total electronic angular momentum of $J=8$. Dysprosium is remarkable in that it contains a pair of nearly degenerate, opposite-parity levels, with $J=10$ which lie at an energy of $19798\, \text{cm}^{-1}$ above the ground state. In addition, Dy has seven stables isotopes at atomic masses of $A=156,\,158$ and $A=160-164$, whereas $\,^{166} Dy$ and $\,^{163} Dy$ have nonzero nuclear spin of $I=\frac{5}{2}$. The energy splitting between these states varies with isotope and ranges from a few MHz up to a few GHz.

**Variation of fundamental constants**

The pair of near-degenerate, opposite-parity states, is highly sensitive to variation of the fine-structure constant $\alpha$, due to large relativistic corrections of opposite sign for the opposite-parity levels. In this unique system, in contrast to atomic-clock comparisons which require optical frequency combs to compare energy levels in different atoms, the difference of the electronic energies of the opposite-parity levels can be monitored directly utilizing a radio-frequency (rf), electric-dipole transition between them. The precision spectroscopy of this energy difference over a period time (for example for a year) can be used to constrain both a temporal variation as well-as a gravitational-potential dependence of** **$\alpha$** **since, during the data-acquisition period, the Earth is located at different values of the gravitational potential of the Sun.

**Parity violation in atomic dysprosium**

The high mass of dyspropsium and the small energy seperation between the opposite-parity states will lead to enhancement of weak mixing effects, making thus $Dy$ a promising system for the study of parity non-conservation. Furthermore, the availability of isotopes with nuclear spin allow for the possibility of measuring the anapole moment.

**References**

- N. Leefer, L. Bougas, D. Antypas, and D. Budker, Towards a new measurement of parity violation in dysprosium, arXiv:1412.1245
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