by Eric Chitambar

The Simulations and Systems Thrust is helping Q-NEXT to advance our understanding of complex physical systems and to identify important new applications for quantum information hardware. The simulation work of this thrust focuses in two complementary directions. The first studies how quantum systems and quantum networks can be reliably modeled and simulated on classical computing hardware. Not only does this help improve our classical computing algorithms and methods, but it also helps establish performance benchmarks and design guidelines for quantum hardware. A second notion of simulation pursued in this thrust seeks to discover new ways in which quantum computers can outperform classical approaches for simulating chemical and condensed matter systems. Much of the Q-NEXT effort in developing new quantum algorithms and applications also belongs to this thrust.

Team members from six of the Q-NEXT partner institutions contribute to the work of the Simulations and Systems Thrust. Many of the projects are collaborative, bringing together expertise from computer science, quantum chemistry and many-body physics. While the majority of researchers in this thrust study the theoretical and computational aspects of quantum information processing, the experimental groups of Mark Saffman (University of Wisconsin) and Hannes Bernien (University of Chicago) have developed neutral atom test beds that can physically implement the algorithms and quantum computing techniques developed by Q-NEXT teammates.

Since the inception of Q-NEXT, the Simulations and Systems Thrust has made key discoveries in the development of near-term quantum computing and networking technologies. In a series of published results, Q-NEXT researchers have improved error mitigation techniques for quantum systems, which involve finding optimal algorithmic designs to combat specific noise characteristics of a given quantum system. On the application side, thrust members have constructed new quantum variational algorithms, which have the potential to solve complex optimization problems by combining high-performance classical computation with smaller-scale quantum computers.

Moving to larger-scale computers and unlocking the full power of quantum computation will require going beyond error mitigation and achieving scalable quantum error correction, a generic term for any method that allows quantum information to be encoded in a noise-tolerant form. One functionality used in many forms of quantum error correction is midcircuit circuit measurement, which involves measuring a quantum system to identify its errors without destroying its encoded information. A key experimental achievement within the Simulations and Systems Thrust has been two separate demonstrations of midcircuit measurement on our neutral-atom platforms. In addition to this work on quantum computing, a powerful tool developed in the thrust is the SeQUeNCe network simulator. By simulating different parts of a quantum network on powerful classical computers, SeQUeNCe is enabling Q-NEXT researchers to envision different strategies for distributing entanglement and computational tasks between different nodes on a real quantum computing network.

The Simulations and Systems Thrust is also actively contributing to the broader Q-NEXT objective of developing the next generation of quantum information scientists. Over 25 total PhD students and postdocs have contributed thus far to research projects within the thrust. In addition, many team members are working to mentor undergraduate students through the form of guided research projects and summer internships.