A new study improves a way to check where a device is. But its safety still depends on what attackers can do.
Checking a claim
A device says it is inside an approved building. How can someone far away check that it is telling the truth?
Scientists study a method called quantum position verification. It uses quantum physics, the rules followed by tiny particles, to test a device's location. A new paper by Wen Yu Kon and colleagues proposes a more flexible method. It appeared in npj Quantum Information on October 31, 2026. It is peer-reviewed theory, released as an accepted article before final editing. It is not a new working location service. 1
An answer with a deadline
Two trusted checking stations send messages toward the claimed location. The device combines their information to choose how to measure a qubit, a unit of quantum information. It sends the measurement result back to both stations. 1
The stations check when the replies arrive. They also compare the replies and score results across many rounds. Both timing and results matter. Signals cannot travel faster than light, so extra delay makes the possible location less precise. 1 4
What the new paper changes
Light signals can be lost on their journey. A useful location check must allow for that loss without making cheating too easy.
The proposed method uses six prepared quantum states, or ways of setting up the qubit. It allows several measurement bases, meaning different choices of how to measure it. The sender need not change its set of states when signal loss changes. These details appear in the publisher's accepted manuscript and the cited author version. 1 2
The team also studies more cheating choices. Attackers can share random information beforehand. They can choose when to claim that no signal was detected based on the messages they receive. Compared with the narrower attack model, accounting for these choices makes the proven requirements stricter: fewer lost signals can be tolerated. 1 2
Why limits still matter
The proof limits attackers' quantum memory, which stores quantum information. It also limits the information produced by certain attack steps. Some possible steps remain outside the proof. 1
Earlier research showed why such limits matter. Attackers with enough shared entanglement, a quantum link between systems, can defeat location checks of this kind. Quantum physics does not make them safe against every attacker. 3
A separate real-world test
A different study, published September 3 in Nature Physics, tested weak laser pulses with checking stations about two kilometers apart. It reported a location range smaller than 75 meters under its own security assumptions. That experiment did not test the October proposal. 4
These studies could help researchers develop location-based access checks. Their value depends on keeping three things clear: timing precision, lost signals, and the attackers covered by the proof. 1 4
Read the research
[3] Position-Based Quantum Cryptography: Impossibility and Constructions
[4] Relativistic position verification with coherent states
The main study is peer-reviewed accepted research shared before final editing. Its final journal version may receive further changes.