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Physical Review A

Tunable atom-light beam splitter using electromagnetically induced transparency

Xinyu Zhu, Rong Wen, J. F. Chen

Published Jun 1, 2018• 3 citations
Publisher

Abstract

With electromagnetically induced transmission (EIT), an optical field can be converted into collective atomic excitation and stored in the atomic medium through switching off the strong-coupling field adiabatically. By varying the power of the coupling pulse, we can control the ratio between the transmitted optical field and the stored atomic mode. We use a cloud of cold $^{85}\mathrm{Rb}$ atoms prepared in magneto-optical trap as the experimental platform. Based on a model of EIT dark-state polariton, we consider the real case where the atomic medium has a finite length. The theoretical calculation gives numerical results that agree well with the experimental data. The results show that the ratio can be changed approximately from 0 to 100%, when the maximum power of the coupling pulse (the pulse length is 100 ns) varies from 0 to 20 mW, in the cold atomic ensemble with an optical depth of 40. This process can be used to achieve an atom-light hybrid beam splitter with tunable splitting ratio and thus find potential application in interferometric measurement and quantum information processing.

DOI
10.1103/physreva.97.063801

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With electromagnetically induced transmission (EIT), an optical field can be converted into collective atomic excitation and stored in the atomic medium through switching off the strong-coupling field adiabatically. By varying the power of the coupling pulse, we can control the ratio between the transmitted optical field and the stored atomic mode. We use a cloud of cold 85Rb^{85}\mathrm{Rb}85Rb atoms prepared in magneto-optical trap as the experimental platform. Based on a model of EIT dark-state polariton, we consider the real case where the atomic medium has a finite length. The theoretical calculation gives numerical results that agree well with the experimental data. The results show that the ratio can be changed approximately from 0 to 100%, when the maximum power of the coupling pulse (the pulse length is 100 ns) varies from 0 to 20 mW, in the cold atomic ensemble with an optical depth of 40. This process can be used to achieve an atom-light hybrid beam splitter with tunable splitting ratio and thus find potential application in interferometric measurement and quantum information processing.
We demonstrate a coherent and dynamic beam splitter based on light storage in cold atoms. An input weak laser pulse is first stored in a cold atom ensemble via electromagnetically-induced transparency (EIT). A set of counter-propagating control fields, applied at a later time, retrieves the stored pulse into two output spatial modes. The high visibility interference between the two output pulses clearly demonstrates that the beam splitting process is coherent. Furthermore, by manipulating the control lasers, it is possible to dynamically control the storage time, the power splitting ratio, the relative phase, and the optical frequencies of the output pulses. With further improvements, the active beam splitter demonstrated in this work might have applications in photonic photonic quantum information and in all-optical information processing.
We experimentally measured the relative contrast of an electromagnetically-induced transparency (EIT) spectrum with two cw lasers in a Λ-type system of magneto-optically trapped 87 Rb atoms, which is a perturbed cold atomic medium. The contrast depends nonlinearly on the power of the coupling beam. Experimental results showed good agreement qualitatively with the simulation results considering the trapping magnetic field gradient, which induced detuning of the coupling laser. We used a free expanding cold atomic cloud that had a temperature of (36 ± 1) µK. To observe the EIT spectrum in the non-perturbed medium, we used two pulsed lasers. We observed that the relative contrast in the unperturbed medium was three times higher than that in the perturbed medium under our experimental conditions.
Quantum information systems require an interface between photons as a physical system to transport information and atoms which are better suited to store and process it. In this thesis the construction of a novel pulsed, bright and narrow-band light source is presented. It consists of an optical parametric oscillator featuring a periodically poled KTP crystal and a mechanical chopper and produces ?s-pulses of squeezed vacuum. The generated states are resonant to the Rubidium-DI-transition, are almost transform-limited and show more than 3 dB of squeezing. The physical effect of electromagnetically induced transparency (EIT) in hot rubidium vapor can be used to generate ultra-low group velocities and allows for a reversible adiabatic conversion of optical quantum states into collective spin excitations which can be used to stop pulses of light. I report about recent progress in slowing down a pulse of squeezed vacuum by one third of its width while still preserving 0.36 dB of squeezing in the process. I analyze electromagnetically induced transparency and light storage in an ensemble of atoms with multiple excited levels (multi-A configuration) which are coupled to one of the ground states by quantized signal fields and to the other one via classical control fields. A basis transformation of atomic and optical states which reduces the analysis of the system to that of electromagnetically induced transparency in a regular three-level configuration is presented. We demonstrate the existence of dark state polaritons and propose a protocol to transfer quantum information from one optical mode to another by adiabatic control of the control fields and present a proof-of principle experiment to adiabatically transfer light between modes of different frequencies in Rb-87 vapor. To that end a digital phase lock circuit has been designed that allows to electronically phase lock an external-cavity diode laser to a reference laser over a 7 GHz frequency range with sub-Hertz precision.
When a coherently prepared atomic medium is confined in an optical cavity, the atomic coherence and interference manifested by electromagnetically induced transparency (EIT) can be manipulated and enhanced by the collective atom–cavity coupling and the cavity feedback. We present an experimental study of the light transmission through an optical cavity coupled with coherently prepared cold Rb atoms. In the frequency domain, the cavity transmission spectrum exhibits spectral peaks representing the cavity normal modes associated with the multi-atom vacuum Rabi splitting and the intra-cavity dark state manifested by the combined EIT effects of the absorption suppression and the steep normal dispersion. In the time domain, a light pulse coupled into the cavity mode propagates with a slow group velocity and the propagation time delay is significantly increased by the cavity feedback.
In this paper, we propose and study a hybrid mechanism for coherent transmission of photons in the coupled resonator optical waveguide (CROW) by incorporating the electromagnetically induced transparency (EIT) effect into the controllable band gap structure of the CROW. Here, the configuration setup of system consists of a CROW with homogeneous couplings and the artificial atoms with $\ensuremath{\Lambda}$-type three levels doped in each cavity. The roles of three levels are completely considered based on a mean field approach where the collection of three-level atoms collectively behave as two-mode spin waves. We show that the dynamics of low excitations of atomic ensemble can be effectively described by a coupling boson model. The exact solutions show that the light pulses can be stopped and stored coherently by adiabatically controlling the classical field.
Electromagnetically induced transparency (EIT) enables an otherwise opaque medium to become transparent and can dramatically slow or even temporarily store light pulses within the medium. It provides a robust platform for manipulating and preserving quantum optical signals, making it a powerful tool for quantum information processing and precision sensing. In this work, we demonstrate EIT on a fully integrated, chip-scale platform based on nanoscale atomic suspended waveguides (NASWAGs) surrounded by hot rubidium vapor. These structures provide submillimeter-scale interaction lengths and feature a tapered geometry that extends the optical mode into the surrounding vapor, increasing the atom-light interaction volume and reducing transit-time broadening. Combined with the strong spatial confinement of both probe and control beams, this enables efficient EIT with only a few microwatts of control power. This represents a significant advance over standard nanophotonic platforms, where weak evanescent fields and short interaction times have previously prevented the observation of EIT.