Science Daily August 20, 2018
According to a team of researchers in the US (Rice University, University of Maryland, industry, UT Austin) when a quantum computer executes an algorithm, it starts at a specific state. The state at the very end is the answer to the algorithm’s question. Reassembling the full state from these measurements, one can later pinpoint hardware or software errors that may have caused the computer to deliver unexpected results. However, the computational cost of reconstruction can be high even as few as five or six qubits. The team solved the validation problem with an algorithm they call Projected Factored Gradient Decent (ProjFGD). It takes advantage of compressed sensing and would cut the number of measurements for a 20-qubit system to a mere million or so. The quantum state tomography tool is generic and has more to do with the nature of the qubit rather than the specific architecture, and it can be scaled up to certify systems…read more.
An illustration shows rubidium atom qubits isolated by scientists at NIST. Credit: NIST