Spectroscopic Methods for Atom Localization and Quantum State Measurement

Muhammad Suhail Zubairy, Sajid Qamar, Shi‐Yao Zhu

D A Murashkin, Sergey A. Saakyan, Vladimir A. Sautenkov +1 more

We have developed an effective spectroscopic method for measure the energy spectra of highly excited ultracold atoms using the registration of resonance fluorescence of atoms in magneto-optical trap during two-step cw excitation of Rydberg states by uv laser. Using this method it was obtained the value of the quantum defect was determined for Rydberg states nD of lithium-7 atoms δ = 0.00192(17).

Monika Schleier-Smith, Ian D. Leroux, Vladan Vuletić

Atomic clocks have reached the Standard Quantum Limit (SQL) of precision,1 set by the projection noise inherent in measurements on uncorrelated atoms. It is possible to overcome this limit by entangling the atoms to generate a "squeezed state" of the atomic ensemble. We use the collective interaction of an atomic ensemble with a far-detuned light field in an optical resonator to prepare squeezed states by two different methods: quantum non-demolition (QND) measurement and Hamiltonian evolution. We apply both methods to an ensemble of 5 x 104 87Rb atoms in a superposition of hyperfine clock states. We measure the suppression of projection noise and compare it to the accompanying reduction in signal, thereby quantifying the net gain in spectroscopic sensitivity. By QND measurement, with resolution up to 9 dB below the projection noise level, we achieve 3.0(8) dB of metrologically relevant squeezing. Whereas the measurement-based approach relies on knowledge of the (randomly distributed) measurement outcome to produce a conditionally squeezed state, the method of Hamiltonian evolution produces a known squeezed state independent of detector performance. We mimic the dynamics of the one-axis twisting Hamiltonian, proposed as a generator of squeezed states by Kitagawa and Ueda,2 by using the atom-induced frequency shift of the resonator mode and the corresponding resonator-field-induced shift of the atomic transition frequency to introduce an effective interaction among the atoms. The resulting deterministic squeezing is sufficient to allow a 6.0(4) dB improvement in spectroscopic sensitivity over the SQL.

Todd Tilma, R. P. Rundle, Ben Davies +2 more

Marc F. M. Trypsteen, Richard M. Walker

Georg Engelhardt, Konstantin Dorfman, Zhedong Zhang

Spectroscopic methods play a vital role in quantum sensing, which uses the quantized nature of atoms or molecules to reach astonishing precision for sensing of, e.g., electric or magnetic fields. In the theoretical treatment, one typically invokes semiclassical methods to describe the light-matter interaction between quantum emitters, e.g., atoms or molecules, and a strong coherent laser field. However, these semiclassical approaches struggle to predict the stochastic measurement fluctuations beyond the mean value, necessary to estimate the sensitivity of spectroscopic quantum sensing protocols. Here, we develop a theoretical framework based on the recently developed photon-resolved Floquet theory (PRFT), which is capable of predicting the measurement statistics describing higher-order cumulants of coherent quantum states of light. The PRFT constructs flow equations for the cumulants of the photonic measurement statistics utilizing only the semiclassical dynamics of the matter system. We apply the PRFT to spectroscopic quantum sensing using dissipative two-level and four-level systems (describing electric-field sensing with Rydberg atoms), and demonstrate how to calculate the Fisher information of the measurement statistics with respect to various system parameters. In doing so, we demonstrate that the PRFT is a flexible tool allowing for improving the sensitivity of spectroscopic quantum sensing devices by several orders of magnitude.