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# CM-AMO SEMINAR

Engineering Photon Statistics in Cavity QED

The capability of engineering photon statistics in quantum circuits has far-reaching applications in quantum information processing. A stream of photons that is both antibunched and sub-Poissonian has a sub-shot noise power level that is below the standard quantum limit and can serve as single-photon light sources; such a non-classical light source will facilitate, for example, absolutely secure quantum communication by preventing information lost due to the use of multiple photons, and quantum computation with linear optics. The opposite effect, photon bunching, describes an ensemble of photons which collectively behaves as a Bose condensate, with an effective de Broglie wavelength that is much smaller than that of constituent photons. Such an orchestrated photonic state could defeat the challenging diffraction limit and make possible deep subwavelength photo-lithography and far-field super-resolution imaging. The low noise property of the bunching state also facilitates a new class of interferometer operating at the fundamental quantum limit.

In this talk, I will report our research on manipulating photon statistics in cavity quantum electrodynamic systems. We have developed a real-space approach that facilitates the investigations of photon-photon correlations for various cavity QED systems [1]. The approach also enables highly efficient numerical computations for the correlated photon transport. In the first part of the talk, I will describe the emergence of a threshold photonic bound state [2,3], and its important role in creating photonic antibunching; I will also discuss the resonance fluorescence in one-dimensional cavity QED [4], and its relation to account for the correlations in the heroic three-dimensional resonance fluorescence experiment of a single trapped ion by Walther et. al. [5] In the second part of the talk, I will report our recent work on optimal photonic antibunching and bunching in cavity QED [6]. Current experimental configurations in cavity quantum electrodynamics to generate photon antibunching relies on the anharmonicity of the Jaynes-Cummings interaction, and operate in the strong coupling regime to create a photon blockade for the transmission field. We investigate numerically the generation characteristics of antibunched photons and show that these systems have a fundamental tradeoff between high transmission and the quality of the antibunched photons, and are also sensitive to dissipation. We further show that optimal antibunching can be achieved in two alternative quantum circuits operating in the dissipatively weak coupling regime such that the two-photon transmission can be two orders of magnitude higher and the quality can be ten times better. Our work represents a new approach to explore fundamentally robust quantum circuit architectures for generating optimal photon antibunching in cavity QED, and also has implications for future cascaded quantum network.