Standardization of quantum state verification using optimal strategies

Illustration of quantum-state verification strategy.

Quantum state plays an important role in quantum information processing. Being able to verify these quantum states reliably and efficiently is an essential step towards practical applications of quantum devices. Typically, a quantum device is designed to output some desired state, but the imperfection in the device’s construction and noise in the operations may result in the actual output state deviating from it.

In this work, the researchers team reports an experimental two-qubit-state verification procedure using both optimal nonadaptive (local measurements) and adaptive (active feed-forward operations) strategies with an optical setup.

A standard way to distinguish these two cases is quantum-state tomography. However, this method is both time-consuming and computationally challenging. Non-tomographic approaches have also been proposed to accomplish the task, yet these methods make some assumptions either on the quantum states or on the available operations. It is then natural to ask whether there exists an efficient non-tomographic approach to accomplish the task?

The answer is affirmative. Quantum-state verification protocol checks the device’s quality efficiently. Various studies have been explored using local measurements. Some earlier works considered the verification of maximally entangled states.

Compared with previous works merely on minimizing the number of measurement settings, the team has minimized the number of copies (i.e., coincidence counts (CCs) in their experiment) required to verify the quantum state generated by the quantum device.

With their methods, they have obtained a comprehensive judgment about the quantum state generated by a quantum device. Present experimental and data analysis workflow may be regarded as a standard procedure for quantum-state verification.

The paper has been published in npj Quantum Information.