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arXiv:0807.3110 · Physical Review A

Ramsey-like measurement of the decoherence rate between Zeeman sublevels

M. Shuker, Ofer Firstenberg, Yoav Sagi, Amit Ben-Kish, Nir Davidson, A. Ron

Published Dec 11, 2008• 21 citations

Abstract

Two-photon processes that involve different sublevels of the ground state of an atom, are highly sensitive to depopulation and decoherence within the ground state. For example, the spectral width of electromagnetically induced transparency resonances in a $\ensuremath{\Lambda}$-type system, are strongly affected by the ground-state depopulation and decoherence rates. We present a direct measurement of decay rates between hyperfine and Zeeman sublevels in the ground state of $^{87}\mathrm{Rb}$ vapor. Similar to the relaxation-in-the-dark technique, pumping lasers are used to prealign the atomic vapor in a well-defined quantum state. The free propagation of the atomic state is monitored using a Ramsey-like method. Coherence times in the range $1--10\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ were measured for room temperature atomic vapor. In the range of the experimental parameters used in this study, the dominant process inducing Zeeman decoherence is the spin-exchange collisions between rubidium atoms.

DOI: 10.1103/physreva.78.063818

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Two-photon processes that involve different sublevels of the ground state of an atom, are highly sensitive to depopulation and decoherence within the ground state. For example, the spectral width of electromagnetically induced transparency resonances in a

\ensuremath{\Lambda}

-type system, are strongly affected by the ground-state depopulation and decoherence rates. We present a direct measurement of decay rates between hyperfine and Zeeman sublevels in the ground state of

^{87}\mathrm{Rb}

vapor. Similar to the relaxation-in-the-dark technique, pumping lasers are used to prealign the atomic vapor in a well-defined quantum state. The free propagation of the atomic state is monitored using a Ramsey-like method. Coherence times in the range

1--10\phantom{\rule{0.3em}{0ex}}\mathrm{ms}

were measured for room temperature atomic vapor. In the range of the experimental parameters used in this study, the dominant process inducing Zeeman decoherence is the spin-exchange collisions between rubidium atoms.

We report characterization of electromagnetically induced transparency (EIT) resonances in the D1 line of (87)Rb under various experimental conditions. The dependence of the EIT linewidth on the power of the pump field was investigated at various temperatures for the ground states of the lambda system associated with different hyperfine levels of the atomic 5S(1/2) state as well as magnetic sublevels of the same hyperfine level. Strictly linear behavior was observed in all cases. A theoretical analysis of our results shows that dephasing in the ground state is the main source of decoherence, with population exchange playing a minor role.

Abstract Hyperfine ground states in alkali atoms are among the most promising candidates for realizing high fidelity scalable quantum information processing architecture. Fast manipulation of ground states can be realized via two-photon transitions driven by lasers. The light-atom interaction can cause decoherence in the system. Here, we study the decoherence rate using accurate lineshape spectroscopy involving hyperfine ground states of D2 transition in 133 Cs atoms in room-temperature-atomic-vapor. The measured decoherence rate varies very slowly as a function of the Rabi frequency of the probe field. Furthermore, we have investigated the slow light group velocity resulting from the narrow spectral width of the electromagnetically induced transparency lineshape. Our study paves the way to implement quantum information processing protocols using coherent photonic polarization qubits in an atomic medium across a large parameter range.

We experimentally studied the temporal evolution of Zeeman electromagnetically induced transparency (EIT) resonances induced by the laser resonant to hyperfine transition of 87Rb in a rubidium buffer gas cell. We simultaneously modulated the laser beam intensity and polarization to achieve the repeated interaction of the laser beam with coherently prepared atoms. Our cell was placed in a homogenous magnetic field to obtain the Larmor precession of the phase of coherences. The weak laser beam was used to probe the atoms at the end of the Ramsey sequence. We measured the transparency of the probe pulse at different magnetic fields for a given excitation pulse and the period of free evolution of Zeeman coherences in the dark. From these data, we reconstructed the temporal evolution of EIT resonances. The Ramsey fringes that appeared on the EIT curves at the beginning of the second probing pulse disappeared at later moments due to various decay processes.

Antirelaxation coatings in atomic vapor cells allow ground-state coherent spin states to survive many collisions with the cell walls. This reduction in the ground-state decoherence rate gives rise to ultranarrow-bandwidth features in electromagnetically induced transparency (EIT) spectra, which can form the basis of, for example, long-time scale slow and stored light, sensitive magnetometers, and precise frequency standards. Here we study, both experimentally and theoretically, how Zeeman EIT contrast and width in paraffin-coated rubidium vapor cells are determined by cell and laser-beam geometry, laser intensity, and atomic density. Using a picture of Ramsey pulse sequences, where atoms alternately spend ``bright'' and ``dark'' time intervals inside and outside the laser beam, we explain the behavior of EIT features in coated cells, highlighting their unique characteristics and potential applications.

An experimental study of electromagnetically induced two- photon transparency (EITT) in rubidium atomic vapor at room temperature is presented. A four level system is considered, involving the two-photon absorption process 5S1/2 to 8S1/2 via an intermediate state 5P3/2, and the single- photon control process 5P3/2 to 5D5/2. A controlling pump laser beam is employed to coherently couple the 5P3/2 and 5D5/2 states, thus producing two dressed intermediate states, which give rise to destructive interference in the two-photon transition. Fluorescence from 8S1/2 to 5P1/2 is used to monitor the 5S1/2(Fequals3) to 8S1/2(Fequals3) two-photon absorption. An induced two-photon transparency of about 80% has been obtained at resonance; the experimental results are in good agreement with the general theory of Agarwal, when the appropriate spectroscopic parameters are employed.