arXiv subjects

Fabian Zschocke

Publications and source records attributed to Fabian Zschocke.

3 recordsLinked to original sources

arXiv2024

Optical interferometer using two-mode squeezed light for enhanced chip-integrated quantum metrology

This work discusses the possibility of using two-mode squeezed light to improve the performance of existing sensor technology with the focus on its miniaturization under realistic losses. Therefore, we analyze a system consisting of a part for the two-mode squeezed light generation, a sensor region and a detection stage. Based on a general four-wave mixing (FWM) Hamiltonian caused by the third order susceptibility, we formulate linearized equations that describe the FWM process below the threshold and are used to analyze the squeezing quality between the generated optical signal and idler modes. For a possible realization, the focus is set on the chip-integrated generation using micro-ring resonators. To do so, the impact of the design and the pump light are considered in the derived equations. These equations are used to analyze the usage of two-mode squeezed light in quantum metrology and the application in a Mach-Zehnder interferometer (MZI). Due to the impact of losses in realistic use cases, we show that the main usage is for small and compact devices, which can lead to a quantum improvement up to a factor of ten in comparison of using coherent light only. This enables the use of small squeezing-enhanced sensors with a performance comparable to larger classical sensors.

quant-ph↗

arXiv2016

Kondo impurities in the Kitaev spin liquid: Numerical renormalization group solution and gauge-flux-driven screening

Kitaev's honeycomb-lattice compass model describes a spin liquid with emergent fractionalized excitations. Here we study the physics of isolated magnetic impurities coupled to the Kitaev spin-liquid host. We reformulate this Kondo-type problem in terms of a many-state quantum impurity coupled to a multichannel bath of Majorana fermions and present the numerically exact solution using Wilson's numerical renormalization group technique. Quantum phase transitions occur as a function of Kondo coupling and locally applied field. At zero field, the impurity moment is partially screened only when it binds an emergent gauge flux, and otherwise becomes free at low temperatures. We show how Majorana degrees of freedom determine the fixed-point properties, make contact with Kondo screening in pseudogap Fermi systems, and discuss effects away from the dilute limit.

cond-mat.str-el↗

arXiv2015

Physical states and finite-size effects in Kitaev's honeycomb model: Bond disorder, spin excitations, and NMR lineshape

Kitaev's compass model on the honeycomb lattice realizes a spin liquid whose emergent excitations are dispersive Majorana fermions and static Z_2 gauge fluxes. We discuss the proper selection of physical states for finite-size simulations in the Majorana representation, based on a recent paper by Pedrocchi, Chesi, and Loss [Phys. Rev. B 84, 165414 (2011)]. Certain physical observables acquire large finite-size effects, in particular if the ground state is not fermion-free, which we prove to generally apply to the system in the gapless phase and with periodic boundary conditions. To illustrate our findings, we compute the static and dynamic spin susceptibilities for finite-size systems. Specifically, we consider random-bond disorder (which preserves the solubility of the model), calculate the distribution of local flux gaps, and extract the NMR lineshape. We also predict a transition to a random-flux state with increasing disorder.

cond-mat.str-el↗