FREE SPACE LAB

HIGHLY-EFFICIENT QUANTUM MEMORY FOR POLARIZATION QUBITS

Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information. A critical figure of merit is the overall storage and retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. In this work we demonstrated a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and efficiency around 68%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. This work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.

The paper: Nature Communications 9, 363 (2018)

Read the Press Release from CNRS and the Story on Phys.org

STORAGE AND RETRIEVAL OF VECTOR BEAMS OF LIGHT IN A MULTIPLE-DEGREE-OF FREEDOM QUANTUM MEMORY

The full structuration of light in the transverse plane, including intensity, phase and polarization, holds the promise of unprecedented capabilities for applications in classical optics as well as in quantum optics and information sciences. Harnessing special topologies can lead to enhanced focusing, data multiplexing or advanced sensing and metrology. In a novel setup, we experimentally demonstrated the storage of such spatio-polarization-patterned beams. A set of vectorial vortex modes was generated via liquid crystal cell with topological charge in the optic axis distribution (q-plate), and preservation of the phase and polarization singularities was demonstrated after retrieval, at the single-photon level. This capability required the simultaneous reversible mapping of the polarization and spatial degrees of freedom : this feature was achieved by combining the spatially multimode nature of the ensemble-based implementation and an additional dual-rail polarization multiplexing. The realized multiple-degree-of-freedom memory can find applications in classical data processing but also in quantum network scenarios where structured states have been shown to provide promising attributes, such as rotational invariance.

This work was done in collaboration with the groups of Fabio Sciarrino
(Roma La Sapienza) and L. Marrucci (Napoli).

The paper : Nature Communications 6, 7706 (2015)
ArXiv version

COHERENT CONTROL OF LIGHT TRANSPORT IN A DENSE AND DISORDERED ATOMIC ENSEMBLE

Light transport in a dense and disordered cold atomic ensemble, where the cooperation of atomic dipoles essentially modifies their coupling with the radiation modes, offers an alternative approach to light-matter interfacing protocols. In this theoretical study, we show how the cooperativity and quasi-static dipole interaction affect the process of light propagation under the conditions of electromagnetically-induced transparency (EIT). We performed comparative analysis of the self-consistent approach with ab-initio microscopic calculations and emphasized the role of the interatomic interaction in the dipoles’ dynamics. Our results show that in such a dense and strongly disordered system the EIT-based light storage protocol stays relatively insensitive to configuration variations and can be obtained with essentially less atoms than it is normally needed for dilute configurations.

This work was done in collaboration with D. Kupriyanov from St Petersburg University.

The paper : Physical Review A 91, 053813 (2015)
ArXiv version

A QUANTUM MEMORY FOR ORBITAL ANGULAR MOMENTUM PHOTONIC QUBITS

Among the optical degrees of freedom, the orbital angular momentum of light provides unique properties, including mechanical torque action with applications for light manipulation, enhanced sensitivity in imaging techniques and potential high-density information coding for optical communication systems. Recent years have also seen a tremendous interest in exploiting orbital angular momentum at the single-photon level in quantum information technologies. In this endeavor, we demonstrated the implementation of a quantum memory for quantum bits encoded in this optical degree of freedom. We generated various qubits with computer-controlled holograms, stored and retrieved them on demand. We further analysed the retrieved states by quantum tomography and thereby demonstrated fidelities exceeding the classical benchmark, confirming the quantum functioning of our storage process. This experiment provide a novel capability for future networks exploring the promises of orbital angular momentum of photons for quantum information applications.

The paper: Nature Photonics 8, 234 (2014)
ArXiv version

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A REVERSIBLE OPTICAL MEMORY FOR TWISTED PHOTONS

In this study, we reported on an experiment in which orbital angular momentum of light is mapped at the single-photon level into and out of a cold atomic ensemble. Based on the dynamic electromagnetically-induced transparency protocol, the demonstrated optical memory enabled the reversible mapping of Laguerre-gaussian modes with preserved handedness of the helical phase structure. The demonstrated capability opened the possibility to the storage of qubits encoded as superpositions of orbital angular momentum states and to multi-dimensional light-matter interfacing.

The paper: Optics Letters 38, 712 (2013)
ArXiv version