Abstract The coherent dynamics and control of spin qubits are fundamental requirements for the development and implementation of quantum technology. However, controlling a single spin qubit within a set of qubits is challenging due to the spatial extent of the applied magnetic field, which can negatively impact the coherent dynamics of neighboring qubits. In this study, a scheme is proposed for characterizing and controlling the coherent dynamics of spin qubits. The proposed scheme comprises a resonator that encloses the desired quantum system and a modulated electron beam that passes through the resonator in close proximity to the qubit of interest. The scheme involves solving the quantum master equation with Lindblad terms to obtain the system's dynamics. Reliability of the proposed model is validated by testing it on a potassium atom, 41 K, and an NV ‐ center in diamond. The results demonstrate that by controlling the parameters of the resonator and electron beam, the coherence and decoherence rates of these quantum systems can be enhanced. The proposed scheme has the potential to characterize various types of spin‐based quantum systems and implement quantum logic gates for quantum computation .
Abstract The coherent dynamics and control of spin qubits are fundamental requirements for the development and implementation of quantum technology. However, controlling a single spin qubit within a set of qubits is challenging due to the spatial extent of the applied magnetic field, which can negatively impact the coherent dynamics of neighboring qubits. In this study, a scheme is proposed for characterizing and controlling the coherent dynamics of spin qubits. The proposed scheme comprises a resonator that encloses the desired quantum system and a modulated electron beam that passes through the resonator in close proximity to the qubit of interest. The scheme involves solving the quantum master equation with Lindblad terms to obtain the system's dynamics. Reliability of the proposed model is validated by testing it on a potassium atom, 41 K, and an NV ‐ center in diamond. The results demonstrate that by controlling the parameters of the resonator and electron beam, the coherence and decoherence rates of these quantum systems can be enhanced. The proposed scheme has the potential to characterize various types of spin‐based quantum systems and implement quantum logic gates for quantum computation .
Abstract Nitrogen vacancy (NV) centers, optically active atomic defects in diamond, have attracted tremendous interest for quantum sensing, network, and computing applications due to their excellent quantum coherence and remarkable versatility in a real, ambient environment. One of the critical challenges to develop NV-based quantum operation platforms results from the difficulty in locally addressing the quantum spin states of individual NV spins in a scalable, energy-efficient manner. Here, we report electrical control of the coherent spin rotation rate of a single-spin qubit in NV-magnet based hybrid quantum systems. By utilizing electrically generated spin currents, we are able to achieve efficient tuning of magnetic damping and the amplitude of the dipole fields generated by a micrometer-sized resonant magnet, enabling electrical control of the Rabi oscillation frequency of NV spins. Our results highlight the potential of NV centers in designing functional hybrid solid-state systems for next-generation quantum-information technologies. The demonstrated coupling between the NV centers and the propagating spin waves harbored by a magnetic insulator further points to the possibility to establish macroscale entanglement between distant spin qubits.
The coherent control of spin qubits forms the basis of many applications in quantum information processing and nanoscale sensing, imaging, and spectroscopy. Such control is conventionally achieved by direct driving of the qubit transition with a resonant global field, typically at microwave frequencies. Here we introduce an approach that relies on the resonant driving of nearby environment spins, whose localized magnetic field in turn drives the qubit when the environmental spin Rabi frequency matches the qubit resonance. This concept of environmentally mediated resonance (EMR) is explored experimentally using a qubit based on a single nitrogen-vacancy (NV) center in diamond, with nearby electronic spins serving as the environmental mediators. We demonstrate EMR driven coherent control of the NV spin state, including the observation of Rabi oscillations, free induction decay, and spin echo. This technique also provides a way to probe the nanoscale environment of spin qubits, which we illustrate by acquisition of electron spin resonance spectra from single NV centers in various settings.
Scattering experiments with energetic particles, such as free electrons, have been historically used to reveal the quantum structure of matter. However, realizing coherent interactions between free-electron beams and solid-state quantum systems has remained out of reach, owing to their intrinsically weak coupling. Realizing such coherent control would open up opportunities for hybrid quantum platforms combining free electrons and solid-state qubits for coincident quantum information processing and nanoscale sensing. Here, we present a framework that employs negatively charged nitrogen-vacancy centers (NV − ) in diamond as quantum sensors of a bunched electron beam. We develop a Lindblad master equation description of the magnetic free-electron–qubit interactions and identify spin relaxometry as a sensitive probe of the interaction. Experimentally, we integrate a confocal fluorescence microscopy setup into a microwave-bunched electron beam line. We monitor charge-state dynamics and assess their impact on key sensing performance metrics (such as spin readout contrast), defining safe operating parameters for quantum sensing experiments. By performing T 1 relaxometry under controlled electron beam exposure, we do not resolve a measurable reduction in T 1 within experimental uncertainty, and instead establish an upper bound on the free-electron–spin coupling strength. Our results establish NV − centers as quantitative probes of free electrons, providing a metrological benchmark for free-electron–qubit coupling under realistic conditions, and chart a route toward solid-state quantum control with electron beams.
Scattering experiments with energetic particles, such as free electrons, have been historically used to reveal the quantum structure of matter. However, realizing coherent interactions between free-electron beams and solid-state quantum systems has remained out of reach, owing to their intrinsically weak coupling. Realizing such coherent control would open up opportunities for hybrid quantum platforms combining free electrons and solid-state qubits for coincident quantum information processing and nanoscale sensing. Here, we present a framework that employs negatively charged nitrogen-vacancy centers (NV-) in diamond as quantum sensors of a bunched electron beam. We develop a Lindblad master equation description of the magnetic free-electron--qubit interactions and identify spin relaxometry as a sensitive probe of the interaction. Experimentally, we integrate a confocal fluorescence microscopy setup into a microwave-bunched electron beam line. We monitor charge-state dynamics and assess their impact on key sensing performance metrics (such as spin readout contrast), defining safe operating parameters for quantum sensing experiments. By performing T1 relaxometry under controlled electron beam exposure, we establish an upper bound on the free-electron--spin coupling strength. Our results establish NV- centers as quantitative probes of free electrons, providing a metrological benchmark for free-electron--qubit coupling under realistic conditions, and chart a route toward solid-state quantum control with electron beams.
Many efforts have succeeded over the last decade at lengthening the timescale in which spin qubits loss quantum information under free evolution. With these design principles at a mature stage, it is now timely to widen the scope and take the whole picture: concerning applications that require user-driven coherent evolutions, qubits should be assessed operating within the desired algorithm. This means to test qubits under external control while relaxation and imperfections are active, and to maximize the algorithm fidelity as the actual figure of merit. Herein, we pose and analytically solve a master equation devised to run one-spin-qubit gate-based algorithms subject to relaxation. It is handled via a home-made code, QBithm, which inputs gate sequences and relaxation rates thus connecting with the longstanding work devoted to their ab initio computation. We evaluate the impact of relaxation and potential experimental imperfections in the calculated fidelities, and implement well-known pulse sequences quantitatively agreeing with experimental data. Hopefully, this work will stimulate the study of many-spin-qubit systems in quantum algorithms, and will serve as a help to design robust spin qubits against decoherence and to perform better-characterized experiments.
By choosing the right system and using the right techniques, it is possible to achieve reliable control of an individual quantum system in a solid. Certain atom-like solid-state systems are especially suited for this goal. The electron spin of the diamond nitrogen-vacancy (NV) impurity center is a leader among such systems and has featured in a great deal of recent experimental work in the context of various quantum technologies. By extending optical control for the NV center we increase the utility of this system, opening it up to fresh applications in quantum optics. \n \nDoing quantum control with a solid-state spin comes with its own challenges. In particular it can be difficult to simultaneously isolate single systems, both for control and from environment-induced decoherence, while also coupling multiple systems together in a controlled way. A goal of the work presented in this dissertation is to develop techniques for answering this problem in the NV center. \n \nOptical control, as opposed to the microwave control usually used for state manipulation in the NV center, would make it easier to address only one spin system at a time. We demonstrate such control using two methods, two-photon optically driven Rabi oscillations and stimulated Raman adiabatic passage. These both have the added advantage that by using Raman-resonant, dipole-detuned optical fields, they protect the spin state from the decoherence normally associated with the optical transitions. Furthermore, we see that this electron spin control is nuclear spin dependent, providing a mechanism for coupling these two spin systems. \n \nWe also investigate a decoherence reduction technique that involves coupling continuous microwave fields to the spin states. The resulting "dressed states" are shielded from spin-bath-induced magnetic field fluctuations. We confirm this using optical coherent population trapping measurements which we have also developed in the NV center. We show that these measurements are sensitive to nuclear spin states as well as to dressed states. \n \nThese results supply the missing piece, optical spin manipulation, to control schemes that are all-optical, and they demonstrate ways to significantly push back the decoherence limit. \n \nThis dissertation includes previously published and unpublished co-authored material.