Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - LIMAStruct (Light-matter interaction with structured light)
Teaser
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...
Summary
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. The capability to coherently interact structured light with atoms could open a variety of applications, which can extend these promises to applications such as quantum networks, including multiplexed long-distance quantum repeaters.
The LIMAStruct project realized at Laboratoire Kastler Brossel in Paris aimed at demonstrating multiplexed light-matter interface experiments based on a large-optical-depth cold atomic ensemble. Firstly, a large optical depth of 300 with a very long cloud of cold atoms, up to 3 cm long, was achieved. Then by using this large atomic ensemble and dual-rail storage, a quantum memory for polarization qubits with a record efficiency of 70%, while maintaining a fidelity with the initial quantum bit beyond 99%, was realized. Finally, a few-mode spatial multiplexer has been aligned and characterized to be integrated into the memory setup.
Work performed
The objectives of the project were the realization of a large optical depth cold atomic ensemble and the demonstration of different multiplexed quantum memory experiments based on this system.
High-OD cold atomic ensemble.
The first experimental key step was the realization of a high-OD cold atomic ensemble. The setup is based on an elongated 2D magneto-optical trap of cesium atoms. The obtained cigar-shaped ensemble has a length of 2.5 cm, and the optical depth is increased by linearly ramping up the magnetic field gradient to radially compress the ensemble. Finally, a large optical depth of 300 has been obtained. Cancellation of residual magnetic field at the few millGauss level has also been achieved.
Highly-efficient quantum memory.
Based on this high-OD cold atomic ensemble, we have demonstrated the quantum storage of polarization qubits with a record efficiency of 70%, while maintaining a fidelity with the initial quantum bit beyond 99%, thereby demonstrating for the first time 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 the elongated ensemble that has been spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. The results have been published in Nature Communications 9 (1), 363 (2018).
Multiplexer system for memory operation.
An optical multiplexer /demultiplexer system was setup to generate a large number of orthogonal LP modes which share the same path at the output in free space. This system has been fully aligned and calibrated. It will be used to investigate the scalability of quantum network protocols taking benefit from spatial multiplexing.
Dissemination.
The different results obtained during the fellowship have been presented in various international conferences in the field of atomic physics, quantum physics and quantum information, such as:
• The 4th Quantum Engineering, from Fundamental Aspects to Application (Nice, France)
• The Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2017, Paris, France)
• The 4th International Conference on optical orbital angular momentum (ICOAM17, Anacapri, Italy)
• The 50th Anniversary European Group on Atomic Systems (EGAS 2018, Kraków, Poland).
• The 26th International Conference on Atomic Physics (ICAP 2018, Barcelona, Spain).
Final results
The fellowship explored different quantum optics experiments based on a large optical depth cold atomic ensemble.
The high-efficiency memory experiment demonstrated the quantum storage of qubits with a record efficiency of 70%. The reported efficiency approaches the maximal performance achievable on the Cesium D2 line, as shown by a developed comprehensive model that includes all the involved atomic transitions. Relative to previous works, this advance has been made possible by combining a high OD medium, efficient spatial multiplexing and low-noise operation. This work work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits. Combined with the multiplexer /demultiplexer system for orthogonal LP modes that has been setup and characterized, this efficient interface will now enable to investigate the scalability of quantum network operations based on spatial multiplexing.
Website & more info
More info: http://quantumnetworks.lkb.ens.fr.