T center defects in silicon provide an attractive platform for quantum technologies due to their unique spin properties and compatibility with mature silicon technologies. We investigate several gate protocols between single T centers, including two probabilistic photon interference-based schemes, a near-deterministic photon scattering gate, and a deterministic magnetic dipole-based scheme. In particular, we study a photon interference-based scheme with feedback which can achieve success probabilities above 50%, and use the photon-count decomposition method to perform the first analytical calculations of its entanglement fidelity and efficiency while accounting for imperfections. We also calculate the fidelity and efficiency of the other schemes. Finally, we compare the performance of all the schemes, considering current and near-future experimental capabilities. In particular, we find that the photon interference-based scheme with feedback has the potential to achieve competitive efficiency and fidelity, making it interesting to explore experimentally.
T center defects in silicon provide an attractive platform for quantum technologies due to their unique spin properties and compatibility with mature silicon technologies. We investigate several gate protocols between single T centers, including two probabilistic photon interference-based schemes, a near-deterministic photon scattering gate, and a deterministic magnetic dipole-based scheme. In particular, we study a photon interference-based scheme with feedback which can achieve success probabilities above 50%, and use the photon-count decomposition method to perform the first analytical calculations of its entanglement fidelity and efficiency while accounting for imperfections. We also calculate the fidelity and efficiency of the other schemes. Finally, we compare the performance of all the schemes, considering current and near-future experimental capabilities. In particular, we find that the photon interference-based scheme with feedback has the potential to achieve competitive efficiency and fidelity, making it interesting to explore experimentally.
Abstract T center defects in silicon provide an attractive platform for quantum technologies due to their unique spin properties and compatibility with mature silicon technologies. We investigate several gate protocols between single T centers, including two probabilistic photon interference-based schemes, a near-deterministic photon scattering gate, and a deterministic magnetic dipole-based scheme. In particular, we study a photon interference-based scheme with feedback which can achieve success probabilities above 50%, and use the photon-count decomposition method to perform the first analytical calculations of its entanglement fidelity and efficiency while accounting for imperfections. We also calculate the fidelity and efficiency of the other schemes. Finally, we compare the performance of all the schemes, considering current and near-future experimental capabilities. In particular, we find that the photon interference-based scheme with feedback has the potential to achieve competitive efficiency and fidelity, making it interesting to explore experimentally.
Implementation of large-scale quantum networks have the potential to augment the capabilities of existing quantum information technologies. By linking quantum processors over photonic channels, future quantum networks could enable applications such as remote quantum sensing, distributed quantum computing, and secure quantum communication. Atomic defects in solids are readily integrated with photonic structures, making them promising candidates for use in quantum networking devices. In particular, the silicon material platform holds great promise due to the technologically mature silicon electronic and photonic industries. The T center defects in silicon possess telecom O-band optical transitions, as well as long-lived electronic and nuclear spins, making it the focus of particular interest. These spin and optical properties of single T centers, together with their accessibility to the existing integrated electronic and photonic technologies, opening the door to modular long-distance quantum networking technologies built on the T center platform. This work outlines the integration of single T centers with a silicon photonic crystal cavity; we observe cavity-enhanced fluorescence emission, resulting in a decay rate enhancement factor of F = 6.89 compared to the bulk emission rate. Through the use of silicon photonic circuits and an angle-polished fiber for light coupling, we achieve a maximum zero phonon line photon outcoupling rate of 73.3 kHz. The design and fabrication of the nanophotonic cavity used in experiment is detailed. This work represents a major step towards use of the silicon T center as a telecom spin-photon interface in future quantum networking applications.
Quantum networks represent one of the most promising technologies for the future development of quantum information science (QIS), with broad applications that range from secure communication and distributed quantum computing to enhanced sensing. Solid-state platforms are ideal candidates for the implementation of such quantum networks, since they offer easy accessibility to device integration and spin-photon interfaces capable of processing and storing qubits, as well as connecting remote network nodes by sending photons through optical fibers. In this thesis, we focus on single T centers, which are a novel type of color centers in silicon. This quantum defect stands out as a promising candidate for quantum networking applications due to its telecom optical transition, superior spin performance, and its compatibility with the technologically mature silicon platform. Here, we present our initial studies on single T centers, including the design and fabrication of nanophotonic devices in a silicon-on-insulator (SOI) sample with integrated T centers, and the cavity-enhanced fluorescence emission of single T centers, which have achieved the highest Purcell factor (Pt = 43) to date. Moreover, our experimental and numerical results allow us to determine a lower bound to the T center quantum efficiency of η = 23.4%, which is a key optical parameter for T centers that is largely overlooked in the community. Additionally, we present preliminary bulk spectroscopy work on ensemble T centers. The same setup will be exploited towards the exploration of novel quantum defects in silicon, including the boron-carbon (B-C) complex defect and the Ti+ defect, which are expected to have similar or better optical properties than the T center.
Robust universal quantum gates with an extremely high fidelity hold an important position in large-scale quantum computing. Here, we propose a scheme for several robust universal photonic quantum gates on a two-or three-photon system, including the controlled-NOT gate, the Toffoli gate, and the Fredkin gate, assisted by low-Q single-sided cavities. In our scheme, the quantum gates are robust against imperfect process occurring with the photons and the electron spins in diamond nitrogen-vacancy (NV) centers inside low-Q cavities. Errors due to the imperfect process are transferred to some heralding responses, which may lead to a direct recycling procedure to remedy the success probability of the quantum gates. As a result, the adverse impact of the imperfect process on fidelity is eliminated, greatly relaxing the restrictions on implementation of various quantum gates in experiments. Furthermore, the scheme is designed in a compact and heralded style, which can increase the robustness against environmental noise and local fluctuation, thus decreasing the operation time, the error probability, and the quantum resource consumption in a large-scale integrated quantum circuit. The near-unity fidelity and not-too-low efficiency with current achievable experimental techniques guarantees the feasibility of the scheme.
Quantum computing offers powerful advantages for simulating quantum many-body systems and for accelerating specific computational tasks beyond classical capabilities, motivating major advances in hardware, control, and error-correction toward scalable and fault-tolerant platforms. Realizing a utility-scale quantum computer requires high-fidelity operations, and hence, the study of hardware errors is of paramount importance. In this thesis, we develop techniques that advance the existing tool sets for analyzing hardware imperfections in quantum operations, thereby enabling a more accurate understanding of how dif-ferent quantum platforms can reach the required fault-tolerance thresholds. In Chapter 3, we study the implementation of two-qubit Controlled-Z (CZ) gates in the solid-state rare-earth platform 171Yb3+:YVO. The chapter compares three different physical routes to en-tangling individual ytterbium ions: direct magnetic dipole–dipole coupling between closely spaced ions, photon scattering mediated by an optical cavity, and heralded gates based on two-photon in-terference, with both cavity-assisted and cavity-free variants. To evaluate these proposals on equal footing, we develop and use theoretical tools for estimating state and gate fidelities in the presence of realistic imperfections. In particular, we apply a perturbative treatment to the magnetic-dipolar gate, while the photon-scattering and photon-interference schemes are analyzed using a combina-tion of existing analytic methods and numerical simulations. This provides a quantitative basis for assessing the feasibility, strengths, and limitations of each mechanism. The comparison shows that the photon-interference-based protocol has the most favorable fidelity scaling with cavity co-operativity, making it the strongest candidate for currently accessible 171Yb3+:YVO parameters. Photon-scattering gates offer the advantage of near-deterministic operation, but this comes at the cost of slower gate times and less favorable cooperativity scaling. The magnetic-dipolar approach, by contrast, gives a fast and deterministic cavity-free gate, but requires ions to be positioned suf-ficiently close together. Although the analysis is carried out for 171Yb3+:YVO as a concrete case study, the techniques used to model, benchmark, and compare these gates are applicable more generally to other solid-state spin-qubit platforms. Motivated by the need for a more systematic treatment of noise in photon-heralded opera-tions, Chapter 4 develops an analytic perturbative method for probabilistic quantum gates between non-interacting emitters. Based on the Zero-Photon-Generation formalism, this method describes light–matter dynamics conditioned on time-integrated photon-detection outcomes and decomposes the resulting conditional map into its ideal contribution and leading noise-dependent corrections. In this way, it produces closed-form expressions for process matrices and effective Pauli error weights, giving a direct link between microscopic hardware imperfections and the noise models used in circuit-level and error-correction descriptions. The method is flexible enough to treat errors from different parts of the experimental architecture, including imperfections in photon emission and optical-control components. We benchmark it on a repeat-until-success CZ gate, where the perturbative results match numerical simulations in the low-error regime, and then use it to study phase-shifter calibration errors as an example of coherent optical-control noise. These results give a physics-informed route for optimizing gate parameters, comparing different imperfections, and constructing effective error models for fault-tolerant quantum computing with hybrid light–matter platforms. Together, these results strengthen the connection between microscopic hardware imperfections and effective error models, providing tools for assessing and optimizing quantum operations on the path toward fault-tolerant quantum computation.
The performance of modular, networked quantum technologies will be strongly dependent upon the quality of their quantum light-matter interconnects. Solid-state colour centres, and in particular T centres in silicon, offer competitive technological and commercial advantages as the basis for quantum networking technologies and distributed quantum computing. These newly rediscovered silicon defects offer direct telecommunications-band photonic emission, long-lived electron and nuclear spin qubits, and proven native integration into industry-standard, CMOS-compatible, silicon-on-insulator (SOI) photonic chips at scale. Here we demonstrate further levels of integration by characterizing T centre spin ensembles in single-mode waveguides in SOI. In addition to measuring long spin T 1 times, we report on the integrated centres’ optical properties. We find that the narrow homogeneous linewidth of these waveguide-integrated emitters is already sufficiently low to predict the future success of remote spin-entangling protocols with only modest cavity Purcell enhancements. We show that further improvements may still be possible by measuring nearly lifetime-limited homogeneous linewidths in isotopically pure bulk crystals. In each case the measured linewidths are more than an order of magnitude lower than previously reported and further support the view that high-performance, large-scale distributed quantum technologies based upon T centres in silicon may be attainable in the near term.