Quantum theory and the computer were arguably the two most profound scientific developments of the twentieth century. Quantum mechanics underpins every fundamental physical science. Computation has made a profound impact on almost every area of life, and science is no exception, with computer simulation extending our understanding in fields ranging from from fluid mechanics to genomics. However, when we apply computation to the study of quantum systems we face fundamental limitations arising from the difference between classical and quantum physics. Quantum mechanics presents serious conceptual challenges, displacing basic classical notions of physical reality such as the deterministic trajectories of Newtonian motion. This means that exact computer simulation of quantum systems often requires tracking many possible outcomes simultaneously, requiring resources which grow rapidly with the size of the system. However, this also implies that computers which operate according to quantum mechanics should have different capabilities than existing classical computers - in particular, they should allow effcient simulation of quantum systems. Simulation of other quantum systems is therefore one of the most promising applications of quantum computing. The number of quantum bits (qubits) required to implement these algorithms is in the few hundreds even for applications beyond the reach of classical computation. The work funded in this proposal will provide a theoretical roadmap of detailed experiments leading us from the few qubit quantum computers of today to the applications on few tens to few hundreds of qubits which can compete with current calculations of scientific interest. We focus on applications of relevance to chemistry, specifically the calculation of molecular energies and simulation of chemical reactions.
The development of even a medium scale quantum computer for quantum simulation would be a technological feat of considerable importance. The work performed in this project will bring this goal closer. Many aspects of this work will be disseminated in the form of a numerical toolkit for quantum simulation, placing the ability to easily design experiments in quantum simulation in the hands of experimental groups. The focus on quantum simulation applied to quantum chemistry means that such experiments will be guided towards the development of devices capable of performing quantum simulations with broad impact in many areas of physical science. The grant will support postdoctoral scholars and undergraduate students at Haverford college and so enhance the research environment for undergraduate students at Haverford college. The educational experience of students outside the physical sciences at Haverford College will be enhanced through the development of a new course for non-majors on foundational questions in quantum mechanics. The impact of this work will also extend beyond the student community through a set of public lectures connected to this new course.
