Quantum memory assisted observable estimation

Quantum, vol. 9, pp. 1655

Abstract

The estimation of many-qubit observables is an essential task of quantum information processing. The generally applicable approach is to decompose the observables into weighted sums of multi-qubit Pauli strings, i.e., tensor products of single-qubit Pauli matrices, which can readily be measured with low-depth Clifford circuits. The accumulation of shot noise in this approach, however, severely limits the achievable variance for a finite number of measurements. We introduce a novel method, dubbed coherent Pauli summation (CPS), that circumvents this limitation by exploiting access to a single-qubit quantum memory in which measurement information can be stored and accumulated. CPS offers a reduction in the required number of measurements for a given variance that scales linearly with the number of Pauli strings in the decomposed observable. Our work demonstrates how a single long-coherence qubit memory can assist the operation of many-qubit quantum devices in a cardinal task.

Authors 4

1. Liubov A. Markovich Aachen Instituut-Lorentz

   Leiden University

   Affiliation as printed

   Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands

2. Attaallah Almasi

   QuTech · Delft University of Technology

   Affiliation as printed

   QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, The Netherlands

3. Sina Zeytinoğlu

   TU Wien · NTT (United States)

   Affiliation as printed

   Institute for Theoretical Physics, TU Wien, Wiedner Hauptstraße 8-10/136, A-1040 Vienna, Austria

   Physics and Informatics Laboratory, NTT Research, Inc., Sunnyvale, California, 94085, The USA

4. Johannes Borregaard

   Harvard University

   Affiliation as printed

   Department of Physics, Harvard University, Cambridge, MA 02138, USA