Magnetic atoms with a large electric dipole moment

Abstract

We experimentally show that an electric dipole moment of more than 1 Debye can be induced in the dysprosium (Dy) atom, in a long-lived state that is about 17513 cm$^{-1}$ above the ground state. This metastable state is part of a strongly coupled opposite-parity doublet. Using optically detected microwave spectroscopy in an atomic beam, we determine the approximately 1.12 cm$^{-1}$ doublet spacing for the five stable bosonic isotopes of Dy with kHz-level accuracy. From the shift of the microwave transition frequency in low electric fields (below 150 V/cm) and from optical spectra in high electric fields (up to 150 kV/cm), a reduced transition dipole moment of 7.65 $\pm$ 0.05 Debye between the doublet states is extracted. In high electric fields the doublet interacts with a third state at 17727 cm$^{-1}$, that connects to the ground state via an electric-dipole transition. The three-state Stark interaction enables preparation of Dy atoms in the metastable state via single-photon excitation from the ground state.

Figures (3)

• Figure 1: (a) Selected energy levels of Dy relevant for this study (not to scale). The quadratic (linear) shift of the $M$-levels of the opposite-parity doublet in weak (strong) electric fields is shown in the left (right) inset. (b) The labeling (state), characteristics (electronic configuration (conf.); parity (p), even (e) or odd(o); total electronic angular momentum ($J$)) and measured energies (E, for $^{162}$Dy, in cm$^{-1}$) of the states are given. In the configuration the common term [Xe]$4f^{10}$ has been omitted. The error bar in the measured energies is $\pm$ 0.002 cm$^{-1}$. The electronic configurations and the energies in the last column are from the NBS Handbook NBS1978, i.e. for $^{162}$Dy. (c) Scheme of the atomic beam machine. Dy atoms are produced by ablation of a rotating Dy rod with pulsed 1064 nm radiation and expand, seeded in a pulse of rare gas, into the source chamber. After the skimmer, in a compact interaction chamber, (i) optical and microwave transitions can be induced in the presence of weak magnetic and electric fields, or (ii) the atomic beam can be exposed to electric fields up to 150 kV/cm. In the detection chamber the Dy atoms are ionized via various REMPI schemes and the ions are mass-selectively detected in a time-of-flight mass spectrometer.
• Figure 2: Ionization detected microwave spectra of the $|b\rangle \rightarrow |a\rangle$ transition for $^{162}$Dy in different magnetic and electric fields. The vertical dashed line indicates the $M_b=0 \rightarrow M_a=0$ transition. a) The $\Delta M=0$ branch in a magnetic field of 2.3 Gauss. b) At $B$=7.6 Gauss, the magnetic-field insensitive $M_b=0 \rightarrow M_a=0$ transition is fully isolated, allowing for the precise determination of $\Delta E$. c) When a weak electric field is added, the $M_b=0 \rightarrow M_a=0$ transition is up-shifted. d) Measured up-shift of the $M_b=0 \rightarrow M_a=0$ transition as a function of the applied electric field.
• Figure 3: Measured excitation spectrum from $|g\rangle$ to the $M$-components that are down-shifted from $E_a$ = 17513.325 cm$^{-1}$ for $^{164}$Dy in an electric field of 148.5 kV/cm. The spectrum is composed of multiple scans over about 0.2 cm$^{-1}$ wide, overlapping intervals.