RUI: CQIS: OP: State-Preparation-and-Measurement Tomography

Reed College, Portland OR

Investigators

Abstract

Quantum mechanics is on the threshold of fundamentally changing modern technology in a number of areas, with new technologies emerging regularly. As these emerge, verification techniques are necessary to ensure confidence and reliability. The primary objective of this project is to develop new ways of uncovering errors that occur in quantum systems, while using a minimum of assumptions about those systems. For example, in quantum communication involving quantum key sharing, it is important for the communications partners to be assured that they have successfully shared a secret key, when in fact they have not. The error detection scheme at the core of this project will let them detect this error, while making a minimum of assumptions about their apparatus. The experiments will advance the movement of quantum technologies from theoretical possibility to actual implementation. These experiments will be performed by undergraduate students, preparing them for scientific careers by exposing them to emerging fields of research and new technologies. Two important operations performed in experiments characterizing quantum systems are (i) preparing systems in particular states and then (ii) performing measurements on those states. State preparation and measurement are usually independent, uncorrelated operations, and when analyzing data it is usually assumed that this is the case. However, if there are indeed correlations between the state preparations and the measurements, it is possible to draw erroneous conclusions from measured data. The primary objective of this project is to experimentally demonstrate a technique called loop state-preparation-and-measurement (SPAM) tomography, which is capable of detecting such correlated errors while making a minimum of assumptions. No assumptions need to be made about either the state preparation or the measurements, other than that the experimenter knows the Hilbert space dimension of the system they are working with. Experiments will be performed on one- and two-qubit systems, with the qubits encoded in the polarizations of individual photons. The group proposes to demonstrate that loop SPAM tomography is capable of detecting correlations between state preparations and measurements of single qubits. They also propose to detect nonlocal correlations between measurements of two qubits in which one party is attempting to fake a Bell inequality violation.