Quantum Optics Colloquium by Sumanta Das
Hybrid systems for Quantum Information processing: from logic gates to quantum networks
In recent years proposals for novel technologies like quantum logic operations and networks have generated immense interest. This is motivated in part by the tremendous progress in engineering, control and manipulation of a diverse range of quantum systems. However, each of these systems face their own distinct challenges towards technological implementation. A viable alternative is the paradigm of hybrid quantum systems, engineered by incorporating different physical components with complimentary functionalities . In this talk I will share with you some of the recent efforts in this direction undertaken by the Theoretical Quantum Optics group at NBI. In particular, I will tell you about an efficient scheme to implement a photonic C-Phase gate. The required optical nonlinearity for operation of such a gate is achieved by using a hybrid configuration of a Rydberg ensemble in a cavity . Furthermore, I will tell you how to engineer an effective light-matter interface for superconducting (SC) qubits, involving waveguides [3,4]. Importantly, I will show that our scheme can work at the level of a single optical photon thereby induces minimal light induced decoherence for the SC qubits . This scheme can potentially open new directions toward future integrable and scalable high-fidelity quantum communication channels and gate operations with optical photons between two distinct SC qubits.
 M. Wallquist, K. Hammerer, P. Rabl, M. Lukin and P. Zoller, Hybrid Quantum Devices and Quantum Engineering, Physica Scripta, T137, 014001 (2009).
 S. Das, A. Grankin, I. Iakoupov, E. Brion, J. Borregaard, R. Boddeda, I. Usmani, A.Ourjoumtsev, P. Grangier, and A. S. Sørensen, Photonic controlled-phase gates through Rydberg blockade in optical cavities, Phys. Rev. A 93, 040303(R) (2016).
 S. Das, V. E. Elfving, S. Faez, and A. S. Sørensen, Interfacing Superconducting Qubits and Single Optical Photons Using Molecules in Waveguides, Phys. Rev. Lett. 118, 140501 (2017).
 S. Das, V. E. Elfving, F. Reiter, A. S. Sørensen, Photon Scattering from a System of Multi-Level Quantum Emitters. II. Application to Emitters Coupled to a 1D Waveguide, arXiv: 1801.03037 (2018).