Non-Gaussian quantum states of optical and mechanical modes: from generating and verifying entanglement to wavefunction collapse
File(s)
Author(s)
Kanari-Naish, Lydia
Type
Thesis
Abstract
Non-Gaussianity plays an important role in quantum information theory and testing outstanding foundational problems. Cavity quantum optomechanics provides a promising experimental platform for quantum science and technology. An outstanding challenge is the generation and verification of a two-mode Schrodinger-cat state in the displacement of two mechanical oscillators. We introduce a protocol to create this state and verify its non-Gaussian entanglement. These entangled states may find exciting applications including fault-tolerant quantum computation, and quantum metrology.
To verify the presence of entanglement, inseparability criteria are explored. The second portion of research builds on this theme: we examine the broader question of choosing appropriate inseparability criteria for arbitrary non-Gaussian states — a typically challenging problem as higher-order moments are required. Focusing on inseparability criteria derived from the property that separable states have a positive partial transpose, we present a statistical framework to quantify the error and consequently the success of such tests. To demonstrate the scope of this method, we identify experimentally-amenable criteria which are tailored towards verifying entanglement in two specific non-Gaussian states; one mechanical and one optical. We also study an optical scheme to measure the relevant bipartite statistical moments needed to assess these criteria.
Thirdly, we explore whether the displacemon device (an electromechanical device consisting of a vibrating nanobeam coupled to a superconducting qubit) can be used to test objective collapse models which have been offered as possible resolutions to the measurement problem and the quantum-to-classical transition. We study two prominent examples of collapse models: Continuous Spontaneous Localization (CSL), and Diosi-Penrose (DP). To investigate these models, a protocol involving qubit manipulations is developed to both generate mechanical non-Gaussian states and probe the subsequent decoherence. We study the experimental requirements necessary to isolate CSL and DP collapse over conventional decoherence.
To verify the presence of entanglement, inseparability criteria are explored. The second portion of research builds on this theme: we examine the broader question of choosing appropriate inseparability criteria for arbitrary non-Gaussian states — a typically challenging problem as higher-order moments are required. Focusing on inseparability criteria derived from the property that separable states have a positive partial transpose, we present a statistical framework to quantify the error and consequently the success of such tests. To demonstrate the scope of this method, we identify experimentally-amenable criteria which are tailored towards verifying entanglement in two specific non-Gaussian states; one mechanical and one optical. We also study an optical scheme to measure the relevant bipartite statistical moments needed to assess these criteria.
Thirdly, we explore whether the displacemon device (an electromechanical device consisting of a vibrating nanobeam coupled to a superconducting qubit) can be used to test objective collapse models which have been offered as possible resolutions to the measurement problem and the quantum-to-classical transition. We study two prominent examples of collapse models: Continuous Spontaneous Localization (CSL), and Diosi-Penrose (DP). To investigate these models, a protocol involving qubit manipulations is developed to both generate mechanical non-Gaussian states and probe the subsequent decoherence. We study the experimental requirements necessary to isolate CSL and DP collapse over conventional decoherence.
Version
Open Access
Date Issued
2023-04
Date Awarded
2023-08
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Vanner, Michael
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)