Researchers Reveal Importance of Passive Control in Noisy Quantum Hardware----Chinese Academy of Sciences

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Researchers Reveal Importance of Passive Control in Noisy Quantum Hardware

Nov 18, 2019

Quantum systems can be exploited for disruptive technologies, but in practice, quantum features are fragile due to noisy environments. The process of “decoherence” stands as one of the major obstacles in realizing scalable quantum technologies.

Quantum coherence is a crucial resource for quantum information processing, which is a basis-dependent property that is known to exhibit resilience to certain types of Markovian noise. Yet, it is still unclear whether this resilience can be relevant in practical tasks.

Recently, the team led by Prof. GUO Guangcan from the University of Science and Technology of China of the Chinese Academy of Sciences first demonstrated the resilient effect of optical quantum coherence to transversal noise, and verified that the measurement precision of entangled Greenberger-Horne-Zeilinger (GHZ) state probes in transverse noise can still beat the standard quantum limit. The study was published in Physical Review Letters.

Through the investigation of the resilient effect of quantum coherence and metrology against transversal noise (the noise is concentrated along a direction perpendicular to signal), the researchers demonstrated the frozen quantum coherence in a four-photon GHZ state when subject to transversal noise.

Besides, they also observed that the quantum Fisher information of the evolved noisy GHZ state is remain unchanged, which means the measurement precision will not decrease when using such a noisy GHZ state for parameter estimation.

The researchers further considered a more realistic scenario in which the noise occurs simultaneously with the signal. The results showed that even subject to a noise strength of equal magnitude to the signal, and the standard quantum limit (the limit of classical system can be achieved) can still be surpassed by using photonic GHZ states up to six-qubit, showing the superiority of the passive noise control scheme.

The experimental results also confirmed that in the case of parallel noise, the entangled GHZ probe will not show any quantum advantage.

Passive noise control schemes can be combined with active error correction in metrology to finally construct efficient quantum metrology protocols in realistic, noisy settings. It would also be attractive to find other applications which can harness the natural resilient effect of quantum resources against decoherence, especially in quantum computation.