RUI: Theoretical Studies of Qubit-Based Environmental Noise Characterization in Solid State Devices

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NON-TECHNICAL SUMMARYThe manipulation of quantum mechanical states opens new possibilities for devices that require quantum mechanics to understand and predict their operation. Applications include quantum information processing, communication, and sensing. Exploiting characteristics of nanoscale solid-state systems that have a quantum mechanical origin is hampered by decoherence, a process that spoils the properties of quantum mechanical states through the uncontrolled interactions between the quantum system and its environment. In recent years a new paradigm to address the issue of decoherence has emerged. Researchers have turned the problem on its head. Rather than using qubits - the fundamental unit of information in a quantum computer to do quantum computation, researchers are using qubits as sensitive probes to extract valuable information about fundamental noise mechanisms.This award supports a theoretical research and undergraduate education program aimed at improving current methods of characterizing noise by elucidating some of the main open questions in noise theory in the context of quantum environments. The outcomes of this research may have impact on quantum-mechanics-based technologies including quantum computation, quantum communication, and quantum metrology. Noise spectroscopy techniques developed in this research may influence the design of the next generation of multiqubit devices, which are expected to be exposed to more complicated noise environments.The program supported through this award will be carried out at Santa Clara University, a Primarily Undergraduate Institution, and will provide educational opportunities for undergraduate students through independent research projects throughout its duration. Students will participate in cutting-edge physics research that will train them in advanced theoretical methods and high-end numerical analysis. A variety of theoretical methods and work modalities will ensure that students will pursue multiple and independent lines of investigation so that self-contained research projects can be completed within a full-time summer period. Participating students will be exposed to the leading experimental and theoretical endeavors in the highly vibrant and interdisciplinary research field of quantum computing.TECHNICAL SUMMARYThis award supports theoretical research and undergraduate education focused on qubit-based environmental noise characterization. The research is aimed to elucidate some of the main open questions in noise detection techniques that utilize qubit readouts under properly chosen dynamical decoupling (DD) pulse sequences to effectively scan the noise power spectrum. Studies will aim at enhancing the resolution and extending the applicability of these DD noise spectroscopy (DDNS) techniques.DDNS protocols for polyspectra reconstruction will be designed to detect signatures of non-Gaussian noise. The method will be applied to study charge fluctuations in solid-state quantum systems, where it can be used as a sensitive tool to map the locations and characteristics of local fluctuators. In a different application, non-Gaussian noise spectroscopy will be used to improve nuclear spin detection using nitrogen vacancy centers in diamond. Multiqubit DDNS techniques will be developed to resolve multiple noise sources and to detect quantum noise in strongly coupled environments. These methods will be applied to study quantum models of interacting fluctuators, revisiting the spin-fluctuator model. The problem of two transverse noises will be analyzed under a general framework, accounting for both dephasing and dissipation, appropriate for a general qubit working point. The theory will be applied to the commonly encountered scenario of quantum dot singlet-triplet spin qubits simultaneously afflicted by charge and nuclear noises. Finally, venturing outside DDNS, other qubit-based methods for environmental noise characterization will be explored, including spin-locking based spectroscopy of continuously driven qubits and correlated projective measurements.The program supported through this award will be carried out at Santa Clara University and will provide educational opportunities for undergraduate students through independent research projects throughout its duration. Students at this primarily-undergraduate institution will become familiar with noise theory, semiconductor physics and foundational quantum mechanics, and will be exposed to a wide range of analytical and numerical methods. Because of the scientific and technological importance of these topics, students will benefit from a research experience that will prepare them for a wide variety of careers in academia and industry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.