Experimental Self-Characterization of Quantum Measurements

Abstract

The accurate and reliable description of measurement devices is a central problem in both observing uniquely non-classical behaviors and realizing quantum technologies from powerful computing to precision metrology. To date quantum tomography is the prevalent tool to characterize quantum detectors. However, such a characterization relies on accurately characterized probe states, rendering reliability of the characterization lost in circular argument. Here we report a self-characterization method of quantum measurements based on reconstructing the response range of the measurement outcomes, eliminating the reliance on known states. We characterize two representative measurements implemented with photonic setups and obtain fidelities above 99.99% with the conventional tomographic reconstructions. This initiates range-based techniques in characterizing quantum systems and foreshadows novel device-independent protocols of quantum information applications. arXiv:1907.07536v1 [quant-ph]

Self-consistent state and measurement tomography with fewer measurements

“…State and measurement operators expressed in different gauges are equivalent, and every observable probability is identical. Each gauge, therefore, corresponds to an arbitrary "reference frame" that one must use to express the operators mathematically [24,25]. For example, by examining Eqs.…”

“…There are some techniques for self-consistently determining the state and/or the POVM if there are no * beckm@reed.edu known states or POVMs. It is possible to perform selfcharacterization of quantum detectors without the need to know any states [24]. Gate-set tomography (GST) is a very general technique, where not only are the state and the POVM determined, but so are the operators describing a series of gate operations that are applied between the state and the measurement [1,[25][26][27].…”

“…Both self-characterization and GST are more general than our technique, in that they do not require known transformations [24,25]. However, because of this they require more measurements.…”

“…Fifty probe states were used in Ref. [24] to self-characterize the detectors, while GST requires at least 56 measurements. The technique we describe here uses 10 measurements to determine both the density operator and the POVM describing a single-qubit system.…”

“…This smaller number of measurements offers an advantage, even if only in time saved, to experimentalists interested in performing these types of experiments. As is the case with most other self-consistent tomography methods, the state and POVM are determined to within a choice of gauge [24,25,39]. We note that operational tomography can eliminate the need to choose a gauge, but requires some a priori knowledge of the system [28].…”