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Quantum Electronics and Laser Science Conference

Evidence of dark state stabilization via the quantum Zeno effect

H. Failache, Paulo Valente, A. Lezama

Published Jun 25, 2003• 0 citations
Publisher

Abstract

Summary form only given. We have studied the decay of the atomic coherence on atoms initially prepared in a dark state (DS) when the coherence (Raman) resonance condition between the atomic system and the light field is suddenly removed. Under this condition, the DS is no longer stationary and its temporal evolution reveals the decay of the atomic coherence. Since in our experiments the DS is created in a ground level and dephasing collisions are negligible, the only possible relaxation channel is through the coupling to the light field. We have studied the influence of the light field intensity on the decay of the atomic coherence. We perform a Hanle type experiment on /sup 87/Rb atoms in a vapor cell.

DOI
10.1109/qels.2002.1031274

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Summary form only given. We have studied the decay of the atomic coherence on atoms initially prepared in a dark state (DS) when the coherence (Raman) resonance condition between the atomic system and the light field is suddenly removed. Under this condition, the DS is no longer stationary and its temporal evolution reveals the decay of the atomic coherence. Since in our experiments the DS is created in a ground level and dephasing collisions are negligible, the only possible relaxation channel is through the coupling to the light field. We have studied the influence of the light field intensity on the decay of the atomic coherence. We perform a Hanle type experiment on /sup 87/Rb atoms in a vapor cell.
The temporal evolutions of coherent resonances corresponding to electromagnetically induced transparency (EIT) and absorption (EIA) were observed in a Hanle absorption experiment carried on the D2D_{2}D2​ lines of % ^{87}Rb vapor by suddenly turning the magnetic field on or off. The main features of the experimental observations are well reproduced by a theoretical model based on Bloch equation where the atomic level degeneracy has been fully accounted for. Similar (opposite phase) evolutions were observed at low optical field intensities for Hanle/EIT or Hanle/EIA resonances. Unlike the Hanle/EIA\ transients which are increasingly shorter for driving field intensities approaching saturation, the B≠0B\neq 0B=0 transient of the Hanle/EIT signal at large driving field intensities present a long decay time approaching the atomic transit time. Such counterintuitive behavior is interpreted as a consequence of the Zeno effect.
Coherent dark states in atoms, created by simultaneous interaction of two coherent light fields with a 3-level system, are of prime importance in quantum state manipulation. They are used extensively in quantum sensing and quantum information applications to build atomic clocks, magnetometers, atomic interferometers and more. Here we study the formation and decay of coherent dark-states in an ensemble of laser-cooled free-falling atoms. We measure the optical-pumping rate into the dark-state in the σ+−σ−σ^+-σ^-σ+−σ− polarization configuration. We find that the pumping rate is linear with the optical field intensity, but about an order-of-magnitude slower than the rate predicted by the commonly used, but simplistic, three-level analytic formula. Using a numerical model we demonstrate that this discrepancy is due to the multi-level Zeeman manifold. Taking into account the slower pumping rate we explain quantitatively the relation between the light-shift and the duration of pumping into dark-state in Ramsey spectroscopy. We also measure the decay of the dark-state coherence and find that in our apparatus it is dominated by the mechanical motion of the atoms out of the probing region, while the atomic decoherence is negligible.
The quantum Zeno and anti-Zeno effects describe how frequent measurements can either suppress or accelerate quantum dynamics. While extensively studied in various platforms, their manifestation in dark-state dynamics remains largely unexplored. Here we investigate the stability of dark states in a cavity quantum electrodynamics (QED) system consisting of two atoms coupled to a single-mode cavity, subject to thermal dephasing that models continuous quantum non-demolition monitoring. Using the Tavis--Cummings model within a Lindblad master equation framework, we perform numerical simulations to investigate how measurement-induced dephasing affects dark-state retention and stabilization time. Through systematic numerical scans, we identify distinct parameter regimes corresponding to Zeno and anti-Zeno behavior: at low dephasing intensities, increasing the measurement strength accelerates the loss of dark-state coherence (anti-Zeno regime), while at higher intensities, it slows down the dynamics and partially recovers dark-state weight (Zeno regime). The transition between these regimes is controlled by the dephasing rates, the cavity photon exchange, and the asymmetry in atom--field couplings. We show that even under strong dephasing, a finite dark-state component persists, demonstrating remarkable robustness. Our results provide insights into the interplay between measurement back-action and decoherence in open quantum systems, with implications for quantum control and information storage.
We have observed coherent Raman beat signals from a Lambda-type three-level system in a sodium atomic vapor. The sample is first prepared in a coherent superposition state of the ground-state hyperfine levels, or a dark state, by resonant bichromatic radiation. A following sudden frequency shift of one of the excitation beams causes the beat signals. Detailed analytical calculations based on the three-level Liouville equations are presented and are compared with experimental results. This simple technique is particularly suited for the obtaining of information on the generated sublevel coherence, including magnitude, phase, and decay time.
The temporal evolutions of electromagnetically induced transparency (EIT) and absorption (EIA) were observed in a Hanle absorption experiment carried on the D2{D}_{2}D2​ lines of 87Rb{}^{87}\mathrm{Rb}87Rb vapor by suddenly turning the magnetic field on or off. The main features of the experimental observations are well reproduced by a theoretical model based on Bloch equation where the atomic level degeneracy has been fully accounted for. Similar (opposite phase) evolutions were observed at low optical-field intensities for Hanle-EIT or Hanle-EIA resonances. Unlike the Hanle-EIA transients that are increasingly shorter for driving field intensities approaching saturation, the $B\ensuremath{\ne}0$ transient of the Hanle-EIT signal at large driving field intensities present a long decay time approaching the atomic transit time. Such counterintuitive behavior is interpreted as a consequence of the Zeno effect.
Transient coherent oscillations in a closed L system under far-off resonant Raman fields were investigated theoretically. It has been found that the coherent superposition of the ground states can be formed due to the absorption even for initial maximal mixed ground states. The absorption oscillates with a period depending on the two-photon detuning when the system is initially in a transparent state and the two-photon Raman detuning is suddenly changed. The amplitude of the absorption decays with the decay rate of the ground states, which is different from the case when the lasers are applied resonantly. These transient coherent oscillations can be used to measure the relaxation rate of the ground states.