Quantum states deployed in fight against GPS spoofing

Quantum information researchers have developed a new quantum position verification (QPV) protocol capable of authenticating a real-time location to better than 75 m—the spatial scale of a single building. The technique addresses the growing security problem of bad actors spoofing location coordinates to breach restricted areas or access secure information, among other schemes.

For example, a ship may sneak into a GPS-protected cargo route by reporting that its position is somewhere else and thus appearing as a false location on the monitoring system. In the past decade, such spoofing incidents have grown more common, with the International Air Transport Association’s 2025 safety report detailing a 193% increase in aircraft GPS spoofing between 2023 and 2025.

Guan-Jie Fan-Yuan, of the University of Science and Technology of China in Hefei, and colleagues have recently introduced a verification protocol that combines classical constraints from special relativity with coherent quantum states to authenticate a location in a way that is secure against spoofing.

To validate an entity’s location, one classical procedure uses trusted verifiers to send a mathematical challenge to an unverified entity, called a prover. The prover then solves the challenge and immediately returns the answer. After multiple repetitions, the verifiers use correct answers, the time between sending the challenges and receiving the answers, and the finite speed of light to determine a true location.

But classical protocols are easily manipulated, Fan-Yuan says. For example, coordinated adversaries can intercept and copy the verifiers’ challenges, exchange information, and return responses that appear to originate from the claimed position, even though the adversaries are located elsewhere. In a classical scenario, the tampering can be done without leaving any evidence.

Fan-Yuan and colleagues introduced a challenge that includes sending a weak coherent quantum state, generated from a phase-randomized laser pulse, alongside the classical challenge messages. To return a correct solution, the prover must measure the polarization of the coherent state in the direction specified by the classical messages. For sufficient repetitions, the likelihood of a successfully spoofed location is exponentially small.

In the team’s approach, two verifiers on opposite sides of the unverified position each send the prover a sequence of classical bits, and one of the verifiers sends the prover a weak coherent quantum state. The team used weak coherent quantum states because of their practicality: The states are loss tolerant, relatively easy to generate, and highly compatible with existing optical and quantum communication technology.

The prover uses the bit sequences to compute a Boolean function that specifies which of two measurement bases to use to measure the polarization of the coherent state and then sends the measurement outcome back to the verifiers for validation. Multiple rounds are needed to collect sufficient statistics and ensure confidence in the verification decision.

The researchers tested their QPV protocol in the lab using the setup shown in the figure. They ran millions of rounds of verification to assess the experimental error rate, accuracy, and measurement latency—the additional time under non-idealized conditions compared with ideal light-speed propagation and an instantaneous prover response. The team reports an overall transmission efficiency of about 70%, an error rate below 0.3%, and about 250 ns of latency. Because light travels about 30 cm in 1 ns, that latency corresponds to a spatial resolution of about 75 m, Fan-Yuan says.

To improve the practical usefulness of their QPV scheme, the team members plan to continue refining its verification precision from tens of meters down to single-meter precision. To achieve that, they will need to further reduce latency by decreasing the prover’s processing time. Fan-Yuan and colleagues also intend to reduce the system’s optical loss to increase the total distance that verifiers can send a challenge, which would allow them to authenticate the position of provers that are farther away.