Quantum communication with cold atoms and optical nanofibers
Overview
We work on a platform of laser cooled atoms which we interface with an optical nanofiber (see Fig. 1). This fiber coupled system creates a toolbox which we use to implement concepts of quantum information and communication. More specifically, both, the generation and storage of non-classical states of light could be implemented within the same platform.
Fig. 1: Left: Scheme of the apparatus: The atoms are laser cooled to a few µK which allows to precisely control and trap them in the evanescent field of an optical nanofiber. Right: Photo of the fiber trap in the vacuum chamber.
Generation of non-classical states of light
The atomic ensemble in the vicinity of the nanofiber provides a strong optical non-linearity and serves as quantum emitters. Based on a recent theoretical proposal [1], we demonstrated that the system can be used to generate photon pairs and single photons [2]. Depending on the number of emitters we continuously tune the transmitted light field from bunching to anti-bunching (See Fig. 2).
Fig2: When traveling through the fiber, the resonant probe light can generate co-propagating photon pairs. This photon pairs interfere with the incoming light, resulting in antibunching and bunching behavior depending on the number of atoms along the nanofiber. More details in [1,2]
Moreover, the non-classicality was confirmed by measuring squeezed states of light transmitted through the ensemble [3]. This allows to characterize the spectral properties of the correlated photons.
Quantum memories
After those measurements our team moved from Vienna to Berlin and the reconstruction of the experiment is finished. Our next step is to go beyond the generation of quantum states of light and investigate the storage of quantum information.
Left: August 2019 Right: August 2020
[1] S. Mahmoodian, M. Čepulkovskis, S. Das, P. Lodahl, K. Hammerer, and AS Sørensen
Strongly Correlated Photon Transport in Waveguide Quantum Electrodynamics with Weakly Coupled Emitters
Phys. Rev. Lett. 121, 143601 (2018)
[2] A.S. Prasad, J. Hinney, S. Mahmoodian, K. Hammerer, S. Rind, P. Schneeweiss, AS Sørensen, J. Volz, and A. Rauschenbag
Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode
Nature Photonics 1 (2020)
arxiv.org/abs/1911.09701
[3] J. Hinney, A. S. Prasad, S. Mahmoodian, K. Hammerer, A. Rauschenbeutel, P. Schneeweiss, J. Volz, M. Schemmer
Unraveling two-photon entanglement via the squeezing spectrum of light traveling through nanofiber-coupled atoms
Phys. Rev. Lett. 127, 123602 (2021)
arxiv.org/abs/2010.09450