Few-Photon Nonlinearity with an Atomic Ensemble in an Optical Cavity

C. Murray, T. Pohl

Andrey Grankin, Philippe Grangier, E. Brion

In a previous Letter [A. Grankin et al., Phys. Rev. Lett. 117, 253602 (2016)] we studied the giant optical nonlinearities of a Rydberg atomic medium within an optical cavity, in the Schwinger-Keldysh formalism. In particular, we calculated the nonlinear contributions to the spectrum of the light transmitted through the cavity. In this article we spell out the essential details of this calculation and we show how it can be extended to higher input photon numbers and higher-order correlation functions. As a relevant example, we calculate and discuss the three-photon correlation function of the transmitted light and discuss its physical significance in terms of the polariton energy levels of the Rydberg medium within the optical cavity.

Thibault Peyronel, Ofer Firstenberg, Qiyu Liang +1 more

Haruka Tanji, Wenlan Chen, Renate Landig +2 more

Engineered strong photon-photon interactions would enable a broad range of applications in quantum information processing. We demonstrate, using an ensemble of atoms strongly coupled to an optical cavity, that light transmission through an opaque medium may be controlled with a few photons and even with the electromagnetic vacuum field. The vacuum field induces 40% transmission, accompanied by a group delay of 25 ns, which corresponds to the light pulse propagating at 1600 m/s through the medium. The transmission increases to 80% when ~10 photons are injected into the cavity. The strong optical nonlinearity at a few-photon level observed in this system opens prospects for advanced quantum devices such as photon-number-state filters.

Pengfei Yang, Xiuwen Xia, Hai Yan He +8 more

Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. The transmission of 18% is achieved for the forward light field, and the maximum blocking ratio for the reverse light is 30 dB. Though the transmission of the forward light can be maximized by optimizing the impedance matching of the cavity, it is ultimately limited by the inherent loss of the scheme. This nonreciprocity can even occur on a few-photon level due to the high optical nonlinearity of the system. The working power can be flexibly tuned by changing the effective number of atoms strongly coupled to the cavity. The idea and result can be applied to optical chips as optical diodes by using fiber-based cavity QED systems. Our work opens up new perspectives for realizing optical nonreciprocity on a few-photon level based on the nonlinearities of atoms strongly coupled to an optical cavity.

Ping Koy Lam, B. C. Buchler