26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Detection-loophole-free nonlocality in the simplest scenario

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Speaker

Ms Nandana Thuranalloor Raveendranath

Description

Quantum nonlocal correlations—encompassing Bell nonlocality and quantum steering—beyond their foundational role, act as a cornerstone for device-independent (DI) applications such as DI quantum key distribution, randomness generation, and more. To ensure the integrity of these protocols, nonlocal correlations must first be rigorously verified using a nonlocality test. This test typically involves parties performing different measurements on their subsystems, with varying numbers of outcomes, and comparing the observed measurement statistics against classically achievable bounds. Such verification must be conducted without any loopholes that could enable malicious parties to imitate nonlocal correlations without entanglement. One of the most difficult loopholes to close, particularly in photonic systems, is the detection loophole, which allows a malicious party to exploit losses to skew measurement statistics and fake nonlocality. To close this loophole, the untrusted party must surpass a specific detection efficiency on their channel and detection apparatus, adding significant complexity to the implementation of a loophole-free nonlocality test. Other factors that contribute to the complexity of the test are determined by the number of distinct measurements and the measurement outcomes that the parties need to perform.

In our work [1], we identify and demonstrate the minimal-complexity protocol for detection-loophole-free quantum steering, a two-party nonlocality test with one untrusted party. We show that a quantum steering test can be completed with only one moderately (>50%) efficient detector on the untrusted side, two measurement settings, and two outcomes (detection or non-detection of a photon). We confirm these predictions through a minimal-complexity experiment with an efficiency as low as $\epsilon = (51.6\pm0.4)\%$ on the untrusted side. We thereby establish the fundamental resource requirements for quantum steering demonstrations, addressing key practical challenges in one-sided device-independent quantum communication and cryptography protocols.

[1]: Raveendranath, Nandana T., et al. "Detection-loophole-free nonlocality in the simplest scenario." arXiv preprint arXiv:2601.03817 (2026).