Efficient tomography for quantum simulations of fermions

September 9, 2021 - Andrew Zhao


Andrew Zhao and Akimasa Miyake, in collaboration with Nicholas Rubin from Google Research, have published a paper in Physical Review Letters detailing a class of protocols to efficiently extract important information out of a quantum computation. For instance, a quantum computer may be used to simulate complex physical systems by directly encoding the simulation into the state of the quantum computer itself. Physical properties, such as energies and reaction rates, can then be calculated by appropriately measuring the state. However, the laws of quantum mechanics prohibit such measurements from revealing all the information encoded in a quantum state within a single round of computation. Thus, many repetitions of the computation are required, a procedure known as quantum tomography.

In their paper, Zhao et al. propose a method to reduce this number of repetitions while retaining all the information relevant to the desired physical properties, thereby speeding up the overall quantum algorithm. Their method is specialized for simulations of fermionic systems, such as chemical molecules or superconducting materials, which require some particular considerations. The authors show that this speedup nearly matches known theoretical limits, and they corroborate this result with numerical calculations, demonstrating the practical efficiency of their method and its improvement upon prior techniques.

The full article can be found online at https://link.aps.org/doi/10.1103/PhysRevLett.127.110504.