FREE SPACE LAB
Félix Hoffet (PhD)
Shuwei Qiu (visiting PhD)
Mingtao Cao (Post-Doc)
Highly-efficient quantum memory
for polarization qubits in a
spatially-multiplexed cold atomic
Nature Communications 9, 363 (2018)
Storage and retrieval of vector
beams of light in a multiple-degree
-of freedom quantum memory
Nature Commun. 6, 7706 (2015)
Quantum state tomography of
OAM photonic qubits via a
projection based technique
New J. Phys. 17, 033037 (2015)
A quantum memory for orbital
angular momentum photonic qubits
Nature Photonics 8, 234 (2014)
FREE SPACE LAB
Controlling the interaction between large atomic ensembles based on cold atomic gases and single photons provides an efficient platform for quantum data storage and entanglement generation. Over the recent years, we have developed a large OD magneto-optical trap and investigated different interfacing protocols for emissive or absorptive memories. We also recently focused on the interaction of structured light (twisted light, vector beams) with such large and multiplexed ensembles, realizing multimode quantum register for different degrees of freedom.
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.
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).
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.
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.
QUANTUM STATE TOMOGRAPHY OF ORBITAL ANGULAR MOMENTUM PHOTONIC QUBITS VIA A PROJECTION BASED TECHNIQUE
While measuring the orbital angular momentum state of bright light beams can be performed using imaging techniques, a full characterization at the single-photon level is challenging. For applications to quantum optics and quantum information science, such characterization is an essential capability. We developed a setup to perform the quantum state tomography of photonic qubits encoded in this degree of freedom. The method is based on a projective technique using spatial mode projection via fork holograms and single-mode fibers inserted into an interferometer. The alignment and calibration of the device is detailed in this study as well as the measurement sequence to reconstruct the associated density matrix. Possible extensions to higher-dimensional spaces are also discussed.
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.