US 11,836,573 B2
Systems and methods for use of a maximally sensitive set of states to identify coherent errors in a quantum system
Daniel Gottesman, Waterloo (CA)
Assigned to KEYSIGHT TECHNOLOGIES CANADA INC., Mississauga (CA)
Filed by Keysight Technologies Canada Inc., Loveland, CO (US)
Filed on Feb. 18, 2021, as Appl. No. 17/179,270.
Claims priority of provisional application 62/978,162, filed on Feb. 18, 2020.
Prior Publication US 2021/0264310 A1, Aug. 26, 2021
Int. Cl. G06F 11/00 (2006.01); G08C 25/00 (2006.01); H03M 13/00 (2006.01); G06N 10/00 (2022.01); G06F 17/18 (2006.01); G06N 10/70 (2022.01)
CPC G06N 10/00 (2019.01) [G06F 17/18 (2013.01); G06N 10/70 (2022.01)] 22 Claims
OG exemplary drawing
 
1. A computer system for identifying coherent error or evolution of interest, the computer system comprising:
at least one processor; and
a memory storing at least one program for execution by the at least one processor, the at least one program comprising instructions for:
(A) for a respective value for n that is a positive integer, performing an outer procedure comprising:
for each respective state in a plurality of states, wherein the plurality of states is sufficient to represent all coherent error or evolution of interest in a quantum system, performing an inner procedure comprising:
(i) creating a copy of the respective state using randomized compiling, wherein the respective state entangles n qudits of the quantum system; and
(ii) obtaining one or more measurements of the n qudits in a measurement basis that corresponds to the plurality of states;
(B) forming a respective outcome bit string for the respective state from each measurement of each qudit in the n qudits;
(C) repeating (A) and (B) a number of times thereby obtaining a corresponding plurality of outcome bit strings for each respective state in the plurality of states;
(D) determining an error rate for each respective state using the corresponding plurality of outcome bit strings for the respective state for the respective value n;
(E) repeating (A) through (D) for each different n drawn from a plurality of positive integers thereby determining an error rate for each respective state for each respective value n in a plurality of values n;
(F) for each respective state S in the plurality of states, fitting the error rate for each respective value n in a plurality of values n obtained for the respective state to a corresponding quadratic function in which the error rate is the dependent variable and n is the independent variable; and
(G) using at least the coefficient for the highest term in each corresponding quadratic function of each respective state to quantify a parameter of the coherent error or evolution of interest.