NSF-BSF: Many-Body Physics of Quantum Computation

NONTECHNICAL SUMMARY This award supports research, education, and outreach activities with a goal to develop theoretical underpinnings and specific quantum algorithms, which may be implemented on the modern-day quantum computation platforms. The last decade witnessed a tremendous progress in the development and manufacturing of prototypical quantum computers. Though still noisy and subject to errors and decoherence, they are already capable of performing non-trivial tasks. This brought a quest for meaningful computational problems, which may be tackled with the help of available quantum architecture. One such problem is optimization, that is finding an outcome (i.e. a sequence of bits), which optimizes a certain intricate set of criteria (known as a cost function). From the physics perspective, this is a problem of finding low energy states (i.e. cooling) of a disordered media (aka glass). The project will implement such glassy landscapes with available qubit platforms and develop cooling protocols utilizing the quantum dynamics of their constituent elements. It was realized that the ideal quantumness greatly facilitates cooling. The project will investigate the effectiveness of real-life noisy-dissipative qubit arrays to accomplish these tasks. It will develop specific algorithms, implement them on commercially available devices (utilizing the NSF Cloud Bank funding mechanism) and compare their performance with theoretical expectations. The award also facilitates the PI's educational and outreach activities which contribute to the development of the US STEM workforce through development of quantum computation curriculum, preparing review articles, organization of workshops, and summer schools. TECHNICAL SUMMARY This award supports research, education, and outreach activities with a goal to develop a theory and protocols for specific quantum algorithms, which may be implemented on commercial platforms, available through the NSF Cloud Bank. On the theory part, the qubit arrays represent examples of open dissipative quantum systems, which are driven by time-dependent local fields and couplings. Such a driven-dissipative environment can be modeled by the Lindbladian. The project will extend theoretical tools of non-equilibrium quantum field theory, to incorporate Lindbladian dynamics. One of the goals of this construction is to elucidate the existence and properties of the many-body localization transition in the Hilbert space of the array. Understanding of such transitions is crucial to developing protocols for the effective quantum cooling (i.e. approximate quantum optimization). Specifically, cooling of the glassy many-body localized phase may be achieved through periodic quantum melting through the first order transition and refreezing through the second order transition. The project will develop a theory of such dissipative cooling cycles and implement them on the D-Wave 5000-qubit platform. It will also develop tools for analyzing the resulting “experimental” data sets. The award also facilitates the PI's educational and outreach activities which contribute to the development of the US STEM workforce through development of quantum computation curriculum, preparing review articles, organization of workshops, and summer schools. 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.