Ultrastrong THz light-matter coupling with Landau levels in 2D semiconductors
J. Keller1, G. L. Paravicini-Bagliani1, F. Appugliese1, C. Maissen1, P. Nataf2, T. Ihn3, K. Ensslin3, C. Lehner3, W. Wegscheider3, M. Beck1, G. Scalari1, J. Faist1
1Institute for Quantum Electronics, Physics Department, ETH Zürich, Zürich, Switzerland
2Institute for Theoretical Physics, Physics Department, ETH Zürich, Zürich, Switzerland
3Institute for Solid State Physics, Physics Department, ETH Zürich, Zürich, Switzerland
Strong light-matter coupling has been recently successfully explored in the GHz and THz [1] range with on-chip platforms. New and intriguing quantum optical phenomena have been predicted in the ultrastrong coupling regime [2], when the coupling strength Ω becomes comparable to the unperturbed frequency of the system ω. We proposed a new experimental platform where the inter-Landau level transition of a high-mobility 2DEG couples to the photonic mode of an LC meta-atom achieving normalized coupling ratios Ω/ω>0.8 [3]. In this poster we will present new experiments exploiting this platform. In the first one we probe the strong-light matter coupling measuring the low temperature longitudinal magnetoresistance of an high mobility GaAs/AlGaAs Hall bar coupled to a meta-atom cavity, performing an energy-resolved tomography of the matter part of the polariton quasiparticle [4]. In the second experiment we engineer a cavity with ultrasmall effective surface [5] were we investigate few-electrons (<100) ultrastrong coupling physics at 300 GHz [6]. In the third experiment we strongly couple an high mobility 2D hole gas in the SiGe/Ge material system and we observe a mode softening of the polariton branches, which clearly deviate from the standard Hopfield model previously verified in cavity quantum electrodynamics. At the largest coupling ratio the lower polariton branch is seen to approach zero frequency [7]. The data are well represented by an effective Hamiltonian possessing the criticality of the Dicke model.
[1] A. Wallraff et al., Nature, Nature 431, 162-167 (2004), Y. Todorov et al., Phys. Rev. Lett. 102, (2009)
[2] C. Ciuti et al., Phys. Rev. B 72, 115303 (2005), A. Ridolfo et al., Phys. Rev. Lett. 110, 163601 (2013)
[3] G. Scalari et al., Science 335, 1323 (2012), C. Maissen et al., Phys. Rev. B 90, 205309 (2014)
[4] G.L. Paravicini-Bagliani et al., in preparation (2018)
[5] A. Benz et al., Nature Comm., 4, 2882 (2013), M. Malerba et al., Appl. Phys. Lett., 109, (2016)
[6] J. Keller, G. Scalari et al., Nano Letters, 17 (12), 7410 (2017)
[7] J. Keller, G. Scalari et al., arXiv 1708.07773