Speaker: Dr. Anton Frisk Kockum (Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden)

Place: Physics Building 208 

Date and Time: 5:00pm on May 1

Title: Entangled states and nonlinear optics using ultrastrong coupling 

Abstract:

In the past decade, ultrastrong coupling between light and matter has transitioned from a theoretical idea to an experimental reality [1]. This is a new regime of quantum light-matter interaction, which goes beyond weak and strong coupling to make the coupling strength comparable to the transition frequencies in the system. In this talk, I will discuss two applications of ultrastrong coupling. 

First, I will show that ultrastrong coupling enables the realisation of analogs of a large number of well-known nonlinear-optics phenomena using only one or more two-level atoms coupled to one or more resonator modes [2]. Through higher-order processes, where virtual photons are created and annihilated, an effective deterministic coupling between two states of such a system (possibly with different number of excitations) can be created. In contrast to most conventional implementations of nonlinear optics, these analogs can reach unit efficiency, only use a minimal number of photons (they do not require any strong external drive), and do not require more than two atomic levels. 

Second, building on the analogs of nonlinear optics, I will introduce a new, simple, and versatile setup for deterministically creating Bell and Greenberger-Horne-Zeilinger (GHZ) states between photons of different frequencies in a two-step protocol [3]. This protocol can be implemented with high fidelity using feasible experimental parameters in state-of-the-art circuit quantum electrodynamics. 

[1] A. F. Kockum et al., Nat. Rev. Phys. 1, 19 (2019). 

[2] A. F. Kockum et al., Phys. Rev. A 95, 063849 (2017). 

[3] V. Macrì et al., Phys. Rev. A 98, 062327 (2018).

Host: Prof. IoChun Hoi