Realization of a Rydberg-Dressed Ramsey Interferometer and Electrometer

We present the experimental realization and characterization of a Ramsey interferometer based on optically trapped ultracold potassium atoms, where one state is continuously coupled by an off-resonant laser field to a highly excited Rydberg state. We show that the observed interference signals can be used to precisely measure the Rydberg atom-light coupling strength as well as the population and coherence decay rates of the Rydberg-dressed states with subkilohertz accuracy and for Rydberg state fractions as small as one part in $10^6$. We also demonstrate an application for measuring small, static electric fields with high sensitivity. This provides the means to combine the outstanding coherence properties of Ramsey interferometers based on atomic ground states with a controllable coupling to strongly interacting states, thus expanding the number of systems suitable for metrological applications and many-body physics studies.

Figure 1

Experimental realization of a Rydberg-dressed Ramsey interferometer. (a) A cloud of ${}^{39}\mathrm{K}$ atoms is prepared in an optical dipole trap and uniformly illuminated by the Rydberg dressing laser. Each atom can be represented by a four level system involving the clock states $|0⟩$ and $|1⟩$, the $|r=39P_{3/2}⟩$ Rydberg state and an auxiliary shelving $|s⟩$. The $|1⟩\to |r⟩$ transition is coupled via the dressing laser with Rabi frequency $\mathrm{\Omega }$ and detuning $\mathrm{\Delta }$ during the Ramsey free evolution time $T$. (b) Ramsey fringes measured in the absence of the dressing laser showing very good coherence and (c) Ramsey fringes with the Rydberg excitation laser on with $\mathrm{\Delta }/2\pi =-12.0\mathrm{MHz}$, showing a modified oscillation frequency and asymmetric decay of the interference contrast. The blue solid lines correspond to fits to the model described in the text.

Figure 2

Analysis of the Ramsey signals as a function of the detuning of the Rydberg dressing laser $\mathrm{\Delta }$. (a) Ramsey oscillation frequency (blue circles) in the presence of the dressing laser extracted from fits to Eq. (6). Gray circles correspond to positive oscillation frequencies before mapping the data. The statistical errors for each measurement are $\lesssim 50\mathrm{Hz}$ (well within the size of the data points). The blue line is a fit to the theoretical model for the dressed-state energy used to determine the atom-light coupling strength $\mathrm{\Omega }$. The dashed line indicates the detuning $\delta$ of the bare clock states. The shaded background shows the Fourier transform of each Ramsey signal. (b) Dressed-state dephasing rate (red squares) and population decay rate (blue circles) as a function of $\mathrm{\Delta }$. The black curve shows the power law ${\mathrm{\Delta }}^{-2}$ which is the expected dependence for intensity-noise dominated dephasing.

Figure 3

Sensitivity of the Rydberg dressed interferometer to small electric fields. (a) Interferogram obtained via spin echo measurement for two different perturbing electric fields for a free evolution time of $T_{\text{echo}}=5\mathrm{ms}$, and with a bias electric field of $F=2.2\mathrm{V}/\mathrm{cm}$. The normalization of the population is for $T_{\text{echo}}=0\mathrm{ms}$, with $\theta =\pi$, which is when the population is maximum. (b) Histograms of 200 measurements at $\theta =5.25\mathrm{rad}$ for the two electric field values.