Method for the differential measurement of phase shifts induced by atoms in an optical ring cavity
Authors: Wang E., Verma G., Tinsley J.N., Poli N., Salvi L.
Autors Affiliation: Univ Firenze, Ist Nazl Fis Nucl, Dipartimento Fis & Astron & LENS, Sez Firenze, Via Sansone 1, I-50019 Sesto Fiorentino, Italy; Abdus Salaam Int Ctr Theoret Phys, Trieste, Italy; CNR, INO, Florence, Italy
Abstract: We demonstrate a method of light phase shift measurement using a high-finesse optical ring cavity which exhibits reduced phase noise due to cavity length fluctuations. Two laser beams with a frequency difference of one cavity free spectral range are simultaneously resonant with the cavity, demonstrating noise correlations in the error signals due to the common-mode cavity length fluctuations. The differential error signal shows a 30 dB reduction in cavity noise down to the noise floor in a frequency range up to half the cavity linewidth (delta nu/2 similar or equal to 30 kHz). Various noise sources are analyzed and their contributions to the noise floor are evaluated. Additionally, we apply this noise-reduced phase shift measurement scheme in a simulated spin-squeezing experiment where we have achieved a factor of 40 improvement in phase sensitivity with a phase resolution of 0.7 mrad, which may remove one important barrier against attaining highly spin-squeezed states. The demonstrated method provides a flexible situation by using an optical ring cavity and two independent beams. This method can find direct application to nondestructive measurements in quantum systems, such as for the generation of spin-squeezed states in atom interferometers and atomic clocks.
Journal/Review: PHYSICAL REVIEW A
Volume: 103 (2) Pages from: 022609-1 to: 022609-9
More Information: We thank G. M. Tino and F. Marin for useful discussions and a critical reading of the manuscript and M. Chiarotti for his contribution in the initial stage of the experiment. We acknowledge financial support from INFN and the Italian Ministry of Education, University, and Research (MIUR) under the Progetto Premiale “Interferometro Atomico” and PRIN 2015. J.N.T., L.S., and N.P. acknowledge support from the European Research Council, Grant No. 772126 (TICTOCGRAV). E.W. acknowledges financial support from the program of the China Scholarship Council (No. 201703170201). G.V. acknowledges the receipt of a fellowship cofunded by the ICTP Programme for Training and Research in Italian Laboratories, Trieste, Italy, and National Research Council, Italy.KeyWords: quantum systemsDOI: 10.1103/PhysRevA.103.022609