# Mainz 2017 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 18: Quantum Effects: Cavity QED I

### Q 18.4: Vortrag

### Dienstag, 7. März 2017, 11:45–12:00, P 4

**Two-Photon Blockade in an Atom-Driven Cavity QED System** — •Karl Nicolas Tolazzi, Christoph Hamsen, Tatjana Wilk, and Gerhard Rempe — Max Planck Institute of Quantum Optics, Hans-Kopfermann-Straße 1, 85748 Garching

N-photon blockade is a dynamical quantum-nonlinear effect in which the absorption of N photons blocks the absorption of N+1 or more photons. This effect occurs in driven systems with an anharmonic ladder of energy eigenstates, e.g. a single atom strongly coupled to a high finesse optical resonator.
While single-photon blockade has been demonstrated in such a system before [1], we here report on the first observation of two-photon blockade [2]. As a signature, we show a three-photon antibunching with simultaneous two-photon bunching observed in the light emitted from the cavity.
The effect occurs for atom driving, not cavity driving. This can be understood intuitively: while a two-level atom can only add excitations to the system one-by-one, the cavity is not restricted in excitation number. The latter leads to bosonic enhancement which causes the transition strengths between the dressed states to increase with the number of excitations in the system while they remain constant for atom driving.
We consider these results as a significant step towards multi-photon quantum nonlinear optics.

Birnbaum et al., Nature 436,87 (2016)

Hamsen et al., arXiv 1608.01571 (2016)