## Strongly interacting photons

Photons usually don't interact with each other. A grand long-term challenge that we try to solve in the quantum optics part of our research is to implement and study strongly interacting photons. In addition to making optical quantum computing and quantum communication more efficient, strongly interacting photons allow for increased precision in imaging and metrology, and also give rise to fascinating many-body physics (e.g. crystallization of photons or novel dissipative time-dependent phenomena). In fact, one could argue that this exciting new direction of many-body physics with strongly interacting photons is the future of quantum optics. One particularly promising approach to achieving strong photon-photon interactions is to use EIT (electromagnetically induced transparency) to couple photons to strongly interacting Rydberg (i.e. highly excited) atoms. Another promising approach involves guiding light and trapping atoms along tapered nanofibers or photonic crystal waveguides. Our work demonstrating interactions between massive photons and showing evidence of two-photon bound states was published in Nature, featured by CNN, and chosen by Physics World as one of ten breakthroughs of 2013.

## Reviews:

- O. Firstenberg, C. S. Adams, S. Hofferberth
**Nonlinear quantum optics mediated by Rydberg interactions**,

J. Phys. B: At. Mol. Opt. Phys. 49 152003 (2016); arXiv:1602.06117 [quant-ph]. - I. Carusotto and C. Ciuti,
**Quantum fluids of light**,

Rev. Mod. Phys. 85, 299 (2013); arXiv:1205.6500 [cond-mat.quant-gas].

## Some recent examples of our work:

- E. Zeuthen, M. J. Gullans, M. F. Maghrebi, A. V. Gorshkov,

**Correlated photon dynamics in dissipative Rydberg media**,

arXiv:1608.06068 [quant-ph]. - C. R. Murray, A. V. Gorshkov, T. Pohl,

**Many-body decoherence dynamics and optimized operation of a single-photon switch**,

New J. Phys. 18 092001 (2016); arXiv:1607.01984 [quant-ph]. - R. M. Wilson, K. W. Mahmud, A. Hu, A. V. Gorshkov, M. Hafezi, M. Foss-Feig,

**Collective phases of strongly interacting cavity photons**,

Phys. Rev. A 94, 033801 (2016); arXiv:1601.06857 [quant-ph]. - M. J. Gullans, Y. Wang, J. D. Thompson, Q.-Y. Liang, V. Vuletic, M. D. Lukin, A. V. Gorshkov,

**Effective Field Theory for Rydberg Polaritons**,

Phys. Rev. Lett. 117, 113601 (2016); arXiv:1605.05651 [physics.atom-ph]. - M. F. Maghrebi, M. J. Gullans, P. Bienias, S. Choi, I. Martin, O. Firstenberg, M. D. Lukin, H. P. Buchler, and A. V. Gorshkov,

**Coulomb bound states of strongly interacting photons**,

Phys. Rev. Lett. 115, 123601 (2015); arXiv:1505.03859 [quant-ph]. - M. F. Maghrebi, N. Y. Yao, M. Hafezi, T. Pohl, O. Firstenberg, and A. V. Gorshkov,

**Fractional Quantum Hall States of Rydberg Polaritons**,

Phys. Rev. A. 91, 033838 (2015); arXiv:1411.6624 [cond-mat.quant-gas]. - P. Bienias, S. Choi, O. Firstenberg, M. F. Maghrebi, M. Gullans, M. D. Lukin, A. V. Gorshkov, H. P. Buchler,

**Scattering resonances and bound states for strongly interacting Rydberg polaritons**,

Phys. Rev. A. 90, 053804 (2014); arXiv:1402.7333 [quant-ph]. - J. S. Douglas, H. Habibian, C.-L. Hung, A. V. Gorshkov, H. J. Kimble, and D. E. Chang,

**Quantum many-body models with cold atoms coupled to photonic crystals**,

Nature Photon. 9, 326 (2015); arXiv:1312.2435 [quant-ph]. - O. Firstenberg, T. Peyronel, Q.-Y. Liang, A. V. Gorshkov, M. D. Lukin, and V. Vuletic,

**Attractive Photons in a Quantum Nonlinear Medium**,

Nature (London) 502, 71 (2013). - A. V. Gorshkov, R. Nath, and T. Pohl,

**Dissipative Many-body Quantum Optics in Rydberg Media**,

Phys. Rev. Lett. 110, 153601 (2013); arxiv:1211.7060 [quant-ph]. - T. Peyronel, O. Firstenberg, Q. Liang, S. Hofferberth, A. V. Gorshkov, T. Pohl, M. D. Lukin, and V. Vuletic,

**Quantum Nonlinear Optics with Single Photons Enabled by Strongly Interacting Atoms**,

Nature 488, 57 (2012). - D. E. Chang, L. Jiang, A. V. Gorshkov, and H. J. Kimble,

**Cavity QED with atomic mirrors**,

New J. Phys. 14, 063003 (2012); arxiv:1201.0643 [quant-ph]. - A. V. Gorshkov, J. Otterbach, M. Fleischhauer, T. Pohl, and M. D. Lukin,

**Photon-photon interactions via Rydberg blockade**,

Phys. Rev. Lett. 107, 133602 (2011); arxiv:1103.3700 [quant-ph]. - A. V. Gorshkov, J. Otterbach, E. Demler, M. Fleischhauer, and M. D. Lukin,

**Photonic phase gate via an exchange of fermionic spin waves in a spin chain**,

Phys. Rev. Lett. 105, 060502 (2010); arXiv:1001.0968 [quant-ph].