Reservoir Engineering for Classical Nonlinear Fields

Reservoir engineering has become a prominent tool to control quantum systems. Recently, there have been first experiments applying it to many-body systems, especially with a view to engineer particle-conserving dissipation for quantum simulations using bosons. In this work, we explore the dissipative dynamics of these systems in the classical limit. We derive a general equation of motion capturing the effective nonlinear dissipation introduced by the bath and apply it to the special case of a Bose-Hubbard model, where it leads to an unconventional type of dissipative nonlinear Schr\"odinger equation. Building on that, we study the dynamics of one and two solitons in such a dissipative classical field theory.Comment: 14 pages, 6 figure

Strain Engineering for Transition Metal Defects in SiC

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology as some of these defects, e.g. vanadium (V), allow for optical emission in one of the telecom bands. For other defects it was shown that straining the crystal can lead to beneficial effects regarding the emission properties. Motivated by this, we theoretically study the main effects of strain on the electronic level structure and optical electric-dipole transitions of the V defect in SiC. In particular we show how strain can be used to engineer the g-tensor, electronic selection rules, and the hyperfine interaction. Based on these insights we discuss optical Lambda systems and a path forward to initializing the quantum state of strained TM defects in SiC.Comment: 14 pages, 6 figure

Nuclear Spin Quantum Memory in Silicon Carbide

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g. vanadium, emit in one of the telecom bands, but the large ground state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long-time coherent storage of quantum states. The proposed nuclear-spin preparation protocol thus marks the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.Comment: 12 Pages, 5 figure

Quantum communication networks with defects in silicon carbide

Quantum communication promises unprecedented communication capabilities enabled by the transmission of quantum states of light. However, current implementations face severe limitations in communication distance due to photon loss. Silicon carbide (SiC) defects have emerged as a promising quantum device platform, offering strong optical transitions, long spin coherence lifetimes and the opportunity for integration with semiconductor devices. Some defects with optical transitions in the telecom range have been identified, allowing to interface with fiber networks without the need for wavelength conversion. These unique properties make SiC an attractive platform for the implementation of quantum nodes for quantum communication networks. We provide an overview of the most prominent defects in SiC and their implementation in spin-photon interfaces. Furthermore, we model a memory-enhanced quantum communication protocol in order to extract the parameters required to surpass a direct point-to-point link performance. Based on these insights, we summarize the key steps required towards the deployment of SiC devices in large-scale quantum communication networks.Comment: 20 pages, 8 figure

Optical Spin-Photon Interfaces with a Focus on Transition Metal Defects in Silicon Carbide

The conversion between stationary and flying qubits is a pillar of numerous quantum technologies such as distributed quantum computing as well as many quantum internet and networking protocols. These quantum technologies promise to use resources, in particular entanglement, not available to classical devices to accomplish tasks that are difficult or even impossible to realize with classical devices. Applications range from fundamental research to secure communication. Because some of these applications require the generation of entanglement, even over large distances, there is substantial interest in efficient interfaces between flying qubits, usually photons, and a stationary memory. In this thesis, we evaluate key aspects of optical spin-photon interfaces, a class of devices combining a stationary qubit memory (spins) and an interface with flying qubits (photons). We focus on defects in silicon carbide (SiC) in which a transition metal (TM) atom substitutes a silicon (Si) atom in the lattice, so that the energy levels with naturally bound quantum states localized around the defect lie within the band gap of SiC. We highlight two key properties of these defects as stationary-flying interconnects: First, they have favorable spin coherence properties and the pertaining nuclear spin of the TM can be used as a quantum memory. Second, they feature a localized and efficient spin-photon interface via their excited states. Defects where vanadium takes the place of a Si atom even allow for photon emission with frequencies in one of the fiber-optic transmission windows, which support efficient transmission in optical fiber. Our results are readily combined with numerical ab-initio and experimental data, providing intuition and further insight into the underlying physics. Additionally, the theoretical assessments of this thesis bridge the gap between the fundamental characterization of TM defects in SiC and their use as spin-photon interfaces in future experiments and quantum technology applications. For instance, the proposed nuclear-spin preparation protocol and spin control mark the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.publishe

Efficient high-fidelity flying qubit shaping

Matter qubit to traveling photonic qubit conversion is the cornerstone of numerous quantum technologies such as distributed quantum computing, as well as several quantum internet and networking protocols. We formulate a theory for stimulated Raman emission which is applicable to a wide range of physical systems, including quantum dots, solid-state defects, and trapped ions, as well as various parameter regimes. We find the upper bound for the photonic pulse emission efficiency of arbitrary matter qubit states for imperfect emitters and show a path forward to optimizing the fidelity. Based on these results, we propose a paradigm shift from optimizing the drive to directly optimizing the temporal mode of the flying qubit using a closed-form expression. Protocols for the production of time-bin encoding and spin-photon entanglement are proposed. Furthermore, the mathematical idea to use input-output theory for pulses to absorb the dominant emission process into the coherent dynamics, followed by a non-Hermitian Schrödinger equation approach, has great potential for studying other physical systems

Reservoir engineering for classical nonlinear fields

Reservoir engineering has become a prominent tool to control quantum systems. Recently, there have been first experiments applying it to many-body systems, especially with a view to engineer particle-conserving dissipation for quantum simulations using bosons. In this paper, we explore the dissipative dynamics of these systems in the classical limit. We derive a general equation of motion capturing the effective nonlinear dissipation introduced by the bath and apply it to the special case of a Bose-Hubbard model, where it leads to an unconventional type of dissipative nonlinear Schrödinger equation. Building on that, we study the dynamics of one and two solitons in such a dissipative classical field theory

Nuclear Spin Quantum Memory in Silicon Carbide

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g. vanadium, emit in one of the telecom bands, but the large ground state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long-time coherent storage of quantum states. The proposed nuclear-spin preparation protocol thus marks the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.publishe

Ultra-narrow inhomogeneous spectral distribution of telecom-wavelength vanadium centres in isotopically-enriched silicon carbide

Spin-active quantum emitters have emerged as a leading platform for quantum technologies. However, one of their major limitations is the large spread in optical emission frequencies, which typically extends over tens of GHz. Here, we investigate single V4+ vanadium centres in 4H-SiC, which feature telecom-wavelength emission and a coherent S  = 1/2 spin state. We perform spectroscopy on single emitters and report the observation of spin-dependent optical transitions, a key requirement for spin-photon interfaces. By engineering the isotopic composition of the SiC matrix, we reduce the inhomogeneous spectral distribution of different emitters down to 100 MHz, significantly smaller than any other single quantum emitter. Additionally, we tailor the dopant concentration to stabilise the telecom-wavelength V4+ charge state, thereby extending its lifetime by at least two orders of magnitude. These results bolster the prospects for single V emitters in SiC as material nodes in scalable telecom quantum networks.publishe