Appendix E

Acronyms and Glossary

LIST OF ACRONYMS

GLOSSARY

Bottom-up chemical synthesis - Creation of atomistically precise and reproducible chemical structures using molecular design, such as classic organic or inorganic methodologies, or atom-by-atom growth through methods such as chemical vapor deposition.

Chemical informatics - The generation, study, and application of chemical information to make data-driven decisions for the understanding, prediction, and design of new molecules and materials.

Chirality-induced spin selectivity - A strategy that is used in chiral molecular systems to manipulate the direction of the electron spin relative to the electron transfer displacement vector. Depending on the chirality of the molecule, the electron spin can align either parallel or antiparallel to the displacement vector.

Clock Transition - A transition between two states where the transition frequency is unchanged by environmental perturbations, such as changes in magnetic or electric field. Shiddiq, M., D. Komijani, Y. Duan, A. Gaita-Ariño, E. Coronado, and S. Hill. 2016. “Enhancing Coherence in Molecular Spin Qubits via Atomic Clock Transitions.” Nature 531(7594):348–351. doi.org/10.1038/nature16984.

Coherence - Classical: Temporal—the time over which the wave phase remains stable; Quantum: A superposition of two states where the resulting state may be described as a linear combination of the two states. Coherence time is a measure of how long a qubit stores quantum information without succumbing to noise. Fox, M. 2006. Quantum Optics: An Introduction. New York: Oxford University Press.

Database - A usually large collection of data organized especially for rapid search and retrieval (as by a computer). Merriam Webster.

Decoherence - Decoherence can be viewed as the loss of information from a system into the environment, degradation of the quantum state, or collapse of the superposition state. Decoherence is often induced by noise. Nielsen, M. A., and I. L. Chuang. 2011. Quantum Computation and Quantum Information, 10th ed. New York: Cambridge University Press.

Defect centers - Spin-bearing defects hosted in extended solids, including, but not limited to, substitutional defects, interstitial defects, dopant atoms, vacancy-dopant pairs, or divacancy defects. Wolfowicz, G., F. J. Heremans, C. P. Anderson, S. Kanai, H. Seo, A. Gali, G. Galli, and D. D. Awschalom. 2021. “Quantum Guidelines for Solid-State Spin Defects.” Nature Reviews Materials 6(10):906–925. doi.org/10.1038/s41578-021-00306-y.

Electronic structure algorithms - These are algorithms (on either quantum or classical computers) that aim to solve or approximate solutions to the electronic structure problem. The electronic structure problem is the problem of solving for the energy (and sometimes wave functions) of electrons interacting with each other and in the Coulomb field of nuclei.

Embedding - Combining high-accuracy calculations (e.g., quantum simulations) with less accurate but more universal calculations to enable the exploration of complex phenomena and systems. Examples of embedding include density matrix embedding theory, dynamical mean field theory, and the concept of a complete active space. Wouters, S., C. A. Jiménez-Hoyos, Q. Sun, and G. K.-L. Chan. 2016. “A Practical Guide to Density Matrix Embedding Theory in Quantum Chemistry.” Journal of Chemical Theory and Computation 12(6):2706–2719. https://doi.org/10.1021/acs.jctc.6b00316.

High-throughput evaluations - Rapidly studying a large set of targets (e.g., molecules) through the use of automation.

Hybrid quantum architectures - This can refer to quantum technologies that make use of disparate quantum technologies (e.g., a system of nitrogen-vacancy center sensors that are coupled to superconducting microwave cavities), or it can refer to systems of processing information that make use of both quantum and conventional classical hardware (e.g., quantum variational algorithms, which use both a quantum computer and a classical computer). McClean, J. R., J. Romero, R. Babbush, and A. Aspuru-Guzik. 2016. “The Theory of Variational Hybrid Quantum-Classical Algorithms.” New Journal of Physics 18(2):023023. doi.org/10.1088/1367-2630/18/2/023023.

Ligand field - The coordination environment around a metal ion is described by a combination of electrostatic interactions (i.e., crystal field theory) and ligand orbitals (i.e., molecular orbital theory). Figgis, B. N. and M. A. Hitchman. 2000. Ligand Field Theory and Its Applications. New York: Wiley-VCH.

Noise models - Models of how noise acts on a quantum system. These range from very idealized/simplistic and easy to simulate to extremely difficult to simulate and also more representative of the physics of a particular noisy device.

Optical cycling - Repeated photon scattering (i.e., relaxation to the starting state) upon continuous excitation between two states, either resonantly or off-resonantly.

Quantum computing - Computation that uses quantum phenomena, such as superposition and entanglement, to solve problems that may be challenging or intractable for classical computing algorithms. Nielsen, M. A., and I. L. Chuang. 2011. Quantum Computation and Quantum Information, 10th ed. New York: Cambridge University Press.

Quantum entanglement - Interaction between two (or more) particles or qubits where the resulting state cannot be described as a product of linear combinations of each individual particle. Entanglement is a type of nonclassical correlation that can be inefficient to simulate classically. Nielsen, M. A., and I. L. Chuang. 2011. Quantum Computation and Quantum Information, 10th ed. New York: Cambridge University Press.

Quantum error mitigation - Distinct from quantum error correction, quantum error mitigation is a large collection of techniques that are employed with the purpose of suppressing the effects of noise on a quantum experiment or computation. Usually, these techniques boil down to capabilities that are (at best) equivalent to being able to detect when an error occurs so that one can postselect on data corresponding to an error-free realization. But since devices with finite error rates per operation compound errors exponentially, these techniques are still intrinsically unscalable. Techniques that fundamentally change this scaling are error correction. Cai, Z., R. Babbush, S. C. Benjamin, S. Endo, W. J. Huggins, Y. Li, J. R. McClean, and T. E. O’Brien. 2022. “Quantum Error Mitigation.” ArXiv. https://arxiv.org/abs/2210.00921.

Quantum information transduction - Coherent conversion of quantum information from one energy scale or storage medium to another (e.g., microwave-to-optical energy conversion). Lauk, N., N. Sinclair, S. Barzanjeh, J. P. Covey, M. Saffman, M. Spiropulu, and C. Simon. 2020. “Perspectives on Quantum Transduction.” Quantum Science and Technology 5(2):020501. doi.org/10.1088/2058-9565/ab788a.

Quantum sensing - Use of a quantum system, quantum properties, or quantum phenomena to perform a measurement of a physical quantity. Degen, C. L., F. Reinhard, and P. Cappellaro. 2017. “Quantum Sensing.” Reviews of Modern Physics 89:035002. doi.org/10.1103/RevModPhys.89.035002.

Sampling approaches - For quantum computing, sampling approaches refer to a method of estimating quantities from a wave function using repeated measurements of local observables. This method is different from a “quantum” approach such as quantum phase estimation.

Scalable quantum architecture - An architecture for quantum computing that can scale to much larger sizes and, ideally, scale to the point of realizing scientifically or commercially valuable computations. Here “architecture” refers to a complete specification for how an information processing system functions. For example, in an error-corrected quantum computer, it would refer not only to the qubit hardware, the control electronics, and the like but also to the way error correction is realized and the classical co-processing that is used to decode the error-correction procedures, etc.