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Non-reciprocity, memory effects, and entanglement in quantum systems

Friday, 7th February 2020

Location: Technische Universität Berlin
Main building, Room H 3005
Straße des 17. Juni 135, 10623 Berlin

Guests are welcome!

Programme

Friday, 7th February 2020

 

Programme
15:00
Topological framework for directional amplification in driven-dissipative cavity arrays
Andreas Nunnenkamp, University of Cambridge, UK

15:50
Coffee Break
16:10
Long-lived polaronic Majorana edge correlation via non-Markovianity
Oliver Kästle, Technische Universität Berlin, Germany
 

16:35
Generation of maximally entangled photon pairs
Kisa Barkemeyer, Technische Universität Berlin, Germany
 
17:00
Informal get-together ("Stammtisch")

Abstracts

Topological framework for directional amplification in driven-dissipative cavity arrays

Andreas Nunnenkamp, University of Cambridge, UK

Directional amplification, in which signals are selectively amplified depending on their direction of propagation, has attracted much attention as a key resource for applications, including quantum information processing. Recently, several, physically very different, directional amplifiers have been proposed and realized in the lab. In this work, we present a unifying framework based on topology to understand non-reciprocity and directional amplification in driven-dissipative cavity arrays. More specifically, we unveil a one-to-one correspondence between a non-zero topological invariant defined on the spectrum of the dynamic matrix of the system and the regimes of directional amplification, in which the end-to-end gain grows exponentially with the number of cavities. We compute analytically the scattering matrix, the gain and reverse gain, showing their explicit dependence on the value of the topological invariant. Parameter regimes achieving directional amplification can be elegantly obtained from a topological `phase diagram', which provides a guiding principle for the design of both phase-preserving and phase-sensitive multimode directional amplifiers. Our results are of direct relevance for optomechanical systems, superconducting circuits, and the emerging field of topolectrical circuits.

References: [1] C.C. Wanjura, M. Brunelli, A. Nunnenkamp, arXiv:1909.11647 (2019).



 

Long-lived polaronic Majorana edge correlation via non-Markovianity

Oliver Kästle, Technische Universität Berlin, Germany

Memory effects and back-action leads to self-synchronization in complex topological materials such asthe Kitaev chain coupled to a phonon reservoir. In contrast to a perfect realization of the 1D Kitaev chainwhich features a gapped energy spectrum and supports Majorana zero modes robust against external perturbations, if a phononic bath is present, dephasing processes arise. If, however, the microscopic properties of the electron-phonon interactions are taken into account, we find a significant suppression of the decoherence, resulting in long-lived edge modes with a high correlation degree due to a finite memory kernel with self-organized equilibration dynamics.



 

Generation of maximally entangled photon pairs

Kisa Barkemeyer, Technische Universität Berlin, Germany

Entanglement lies at the heart of many applications in the field of quantum information processing. As a platform for their implementation, photonic degrees of freedom are promising candidates. Photon pairs entangled in their polarization degrees of freedom are, for example, generated in a quantum dot biexciton cascade. We show that the additional presence of spin flips does not change the dynamics of the system qualitatively as the Hamiltonian of a system with spin flips and fine-structure splitting is isomorphic to the one of a system in which no spin flips occur. Furthermore, photon pairs can be entangled in time and energy.  We discuss first steps and ideas to use coherent-delayed feedback to control this type of entanglement in Franson type interferometric setups.

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