A Multi-Copy Approach to Quantum Entanglement Characterization

An accurate evaluation of the performance of quantum entanglement sources-based on various physical realizations and designed for application in numerous quantum protocols-requires a thorough characterization of the ensemble of the generated output quantum states. This presents a great challenge, as numerous measurements, such as full state tomography, need to be performed on the ensemble. This incentivizes us to reduce the overall duration of the characterization procedure, so that time is saved and the effect of setup drift reduced. For many physical realizations of the quantum states, including polarization and path-encoded qubits, a traveling salesman problem of finding the optimal order of tomographic projections can be found and solved [1]. The achieved tomography speedup, found and experimentally verified [2,3] for up to six-qubit systems, is seen to increase with the size of the quantum system in question, see Fig. 1(a). For three-qubit systems already, the time spent on setting the measurement projections can be halved. A step-by-step workflow [4] is introduced to suit various tomographic scenarios.