Economical standard quantum process tomography

TL;DR

This paper presents an economical method for quantum process tomography that characterizes specific elements of the process matrix without requiring ancilla systems, using minimal experimental settings and suitable operator bases.

Contribution

The authors develop a standard quantum process tomography scheme that efficiently characterizes individual process matrix elements without ancilla, reducing experimental complexity.

Findings

Single experimental run suffices for a selected matrix element.

Number of settings does not exceed 2N for N-qubit systems.

Applicable when controlled two-body interactions are unavailable or undesirable.

Abstract

Recently, Bendersky \emph{et al.} developed a method to complete the task of characterizing an arbitrary $\chi$ matrix element in a scalable way, Phys. Rev. Lett. Vol. \textbf{100}, 190403(2008), where an auxiliary system was needed. In present work, we shall show that the same task can also be completed within the scheme of standard quantum process tomography (SQPT) where there is no requirement for ancilla. Our method depends on two observations: With the elaborately chosen operators basis, the SQPT may have an economical form where a single run of experiment, in which we measure the expectation value of a chosen operator in the outport of the quantum channel with a known input, is sufficient to characterize a selected $\chi$ matrix element; With the progress recently achieved in quantum entanglement detection, we also find that the number of the experimental settings to realize the experiment for the selected $\chi$ matrix element does not exceed 2N for the N-qubits system. For practice, our scheme can be applied for the cases where the controlled two-body interaction is neither available nor desirable.