Electron Electric Dipole Moment Searches Using Clock Transitions in Ultracold Molecules

Permanent electric dipole moments (EDMs) of fundamental particles such as the electron are signatures of parity and time-reversal violation occurring in physics beyond the standard model. EDM measurements probe new physics at energy scales well beyond the reach of present-day colliders. Recent advances in assembling molecules from ultracold atoms have opened up new opportunities for improving the reach of EDM experiments. However, the magnetic field sensitivity of such ultracold molecules means that new measurement techniques are needed before these opportunities can be fully exploited. We present a technique that takes advantage of magnetically insensitive hyperfine clock transitions in polar molecules, offering a way to improve both the precision and accuracy of EDM searches with ultracold assembled molecules.

Figure 1

Magnetic field ${\mathcal{B}}_z(t)$ (black, dotted line) and molecular orientation $\zeta (t)$ (red, solid line). The curve for $\zeta (t)$ is in response to an electric field ${\mathcal{E}}_z(t)={\mathcal{E}}_0\cos (\omega t+\beta )$ and is calculated using the methods in [29], Sec. A. The nonlinear response of $\zeta$ to ${\mathcal{E}}_z$ is evident. The red dashed line shows the first harmonic of $\omega$ contained in $\zeta (t)$, which drives the hyperfine transition.

Figure 2

The population transfer is shown on a Bloch sphere for the two clock states in the presence of oscillating electric and magnetic fields. The $P$, $T$-violating Hamiltonian leads to an extra transition amplitude ${\mathrm{\Omega }}_{PT}\tau$ that interferes with the transition amplitude ${\mathrm{\Omega }}_B\tau$ due to the oscillating magnetic field. The case shown here corresponds to $\beta =0$, where these amplitudes add constructively.

Figure 3

The population in the excited clock state, $|e⟩$, as a function of interaction time, when the electric and magnetic fields are on resonance (${\mathrm{\Omega }}_{PT}$ is exaggerated for illustration). The relative phase $\beta$ between the electric and magnetic fields can be varied to distinguish the $P$, $T$-violating transition amplitude from that due to the magnetic field.