Researchers Achieve Optimal Quantum State Verification Through Experiments

In the field of quantum information, information is encoded into quantum states. When compared to classical equivalents, more secure cryptography and more efficient computations can be performed by leveraging the “quantumness” of these states.

Under the guidance of Prof. GUO Guangcan from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), a team of researchers tuned the original hypotheses to be robust to practical defects.

Their aim was also to experimentally execute a scalable quantum state verification on two-qubit and four-qubit entangled states using nonadaptive local measurements. The study outcomes were reported on July 17th, 2020, in the Physical Review Letters journal.

One feature that is critical to quantum information science is the initialization of a quantum system into a specific state.

A range of measurement approaches has been created to describe how well the system is initialized. However, for any specified system, there often exists a trade-off between its efficiency and the accessible information of the quantum state.

Traditional quantum state tomography can be used to describe unidentified states, though it requires exponentially high-cost laborious postprocessing.

On the other hand, the latest theoretical advancements reveal that quantum state verification offers a means to measure the prepared state with considerably fewer samples, specifically in the case of multipartite entangled states.

For all the states tested as part of the study headed by Prof. GUO Guangcan, the predicted infidelity is inversely proportional to the number of samples, which demonstrates the power to describe a quantum state with a fewer number of samples.

When compared to the universally optimal approach that necessitates nonlocal measurements, the efficiency of the new experiment is worse only by a minuscule constant factor of less than 2.5.

The difference in performance between quantum state tomography and quantum state verification in an experiment was compared to describe a four-photon Greenberger-Horne-Zeilinger state. The results of the comparison reveal the advantage of quantum state verification with respect to both the realized precision and efficiency.

The researchers experimentally achieved an optimal quantum state verification (QSV) that was easy to execute and robust with respect to realistic defects. The 1/n scaling results demonstrated from the new approach were achieved without adaptive or entangled measurements.

The results of this study have evident implications for several quantum measurement tasks and could be applied as a rigid basis for further studies on more complex quantum systems.

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