Postdoctoral fellow at the Institute for Quantum Computing (IQC) Aharon Brodutch and Eliahu Cohen (Tel Aviv University, University of Bristol) have developed a new method for designing complex quantum measurements.
Measurements are necessary for determining observable quantities – they tell us about the outcome of a quantum protocol and can also be part of a control sequence, such as an error detection and correction scheme. Brodutch and Cohen looked specifically at projective measurements – measurements that project the state of the system into a new state corresponding to the result. For example, when measuring spin, if the spin was ‘up’ and the resulting measurement is ‘up’, the spin remains ‘up’.
The researchers used the von Neumann measurement scheme and a quantum eraser to model a measurement that requires specific interactions between two physical systems that are challenging to construct. Brodutch and Cohen presented a protocol for carrying out non-local measurements – projective measurements of observable quantities on a system with parts at different locations. First, they performed simpler measurements that revealed too much information about the system and then erased parts of the results. The local measurement is erased, or undone, by making a conjugate, or incompatible, measurement and post-selecting the result.
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