Symposium QT07—Atomic and Molecular Quantum Systems and Defect Engineering for Quantum Technologies

Single atom impurities and point defects in solid and molecular semiconductors and insulators have been observed to be excellent quantum systems that behave as qubits or single photon emitters. They can have long lived spin degrees of freedom suitable for quantum information processing, optical transitions that allow for coupling to photons, and promise to push quantum technologies beyond cryogenic environments. These properties spurred intense global interest in further developing such quantum defects as qubits, quantum memories, quantum registers, and single photon sources. However, the intrinsic fragility of quantum states poses a major materials science challenge and building a device that utilizes quantum states requires attention to decoherence-causing defects. For example, qubits based on shallow donors in silicon require close proximity to dielectric interfaces and metal gates to enable control, but can lead to loss of quantum information, rendering defect minimization important. Optical applications of quantum defects require integration into nanophotonic devices, introducing microfabricated surfaces that can host defects that lead to magnetic and electric field noise. In superconducting qubits, defects can act as two-level systems that cause dielectric loss and decoherence. These problems can be circumvented by learning to diagnose and control surfaces and interfaces, and by designing qubits that are insensitive to such issues. Enhanced understanding of defect measurements, manipulation, and modeling is essential but still lacking: Being able to control defects and impurities at the single emitter level and, or even knowing what the defect is, creates challenges that need to be addressed before significant progress can be made, motivating this symposium.

Challenges related to the controlled synthesis of impurities with desired defect spacing and defect type, occur e.g. for diamond or silicon carbide hosts, and low-dimensional materials, such as single-layer boron nitride. In particular, quantum sensing and quantum optics require specific defects in high-quality hosts. Nitrogen-vacancy centers in diamond, for example, can be synthesized using ultrashort laser pulses, but the role of electronic excitations and non-adiabatic mechanisms versus lattice annealing remains an open question. Similarly, techniques for positioning arrays of rare-earth ions in oxides need further development. Challenges for characterization include charge and spin states of defects, to assess suitability as single photon quantum emitters or qubits with long-term stability of their spin excitations. Modeling coupling between quantum defects poses challenges in its own right: Accurately understanding real-time dynamics, electronic and spin excited-state lifetimes, and non-adiabatic electron-ion effects complicates the description, hampering a connection to experiment.

• Materials synthesis and characterization
• Semiconductors, insulators, wide-band-gap materials
• Low-dimensional materials
• Computational and theoretical modeling
• Defect manipulation
• Hybrid quantum devices
• Identification and control of sources of decoherence
• Characterization and modeling of qubits and single-photon emitters

• Igor Aharonovich (University of Technology Sydney, Australia)
• David Awschalom (The University of Chicago, USA)
• Nathalie de Leon (Princeton University, USA)
• Sudipta Dubey (Indian Institute of Technology Kanpur, India)
• Danna Freedman (Northwestern University, USA)
• Kai-Mei Fu (University of Washington, USA)
• Adam Gali (Wigner Fizikai Kutatóközpont, Hungary)
• Giulia Galli (The University of Chicago, USA)
• Weibo Gao (Nanyang Technological University, Singapore)
• Andreas Heinrich (Center for Quantum Nanoscience, Republic of Korea)
• Stephen Jesse (Oak Ridge National Laboratory, USA)
• Ute Kaiser (Universität Ulm, Germany)
• Prineha Narang (Harvard University, USA)
• Kasturi Saha (Indian Institute of Technology Bombay, India)
• Michelle Simmons (University of New South Wales, Australia)
• Nick Vamivakas (University of Rochester, USA)
• Chris G. Van de Walle (University of California, Santa Barbara, USA)