Ensuring that all votes are tallied while remaining completely private poses a challenge in any election. Quantum mechanics could provide a solution.
A voting system that combines mathematical methods with quantum techniques can theoretically ensure every ballot is counted without revealing identities. Recent experiments have confirmed the approach functions as intended.
Several nations already employ electronic voting, with vendors offering various safeguards against interference. Quantum physics could elevate these protections by making tampering impossible in principle.
Researchers in France previously outlined the theoretical basis for this quantum voting method. Both the original group and an independent team have now conducted practical tests.
To illustrate the process, imagine four individuals choosing between mushroom stew and tofu stir-fry. They distrust one another and any external administrator, so they adopt the quantum protocol instead of paper ballots.
The system requires four voting rounds matching the number of participants. Each person receives a unique secret index from 1 to 4 and votes only in their assigned round. They also get a random secret bit of 0 or 1, with the total number of 1s kept even.
In each round, participants without a matching index send their bit. The matching voter either keeps the bit to select one option or flips it for the other. Observers see only random bits, preventing identification of individual votes.
Votes are tallied by checking whether the parity of 1s remains even. Changes occur only when someone selects the alternative option.
If the distributor of bits and indexes cannot be trusted, quantum mechanics addresses this by using four entangled photons instead of classical bits. Lasers directed at a crystal generate these photons, ensuring no one knows the initial state. Tampering with any photon is detectable through measurements on the others.
Tests have covered scenarios with two choices and four voters, as well as 16 choices and eight voters.
Mark Hillery of Hunter College notes these are useful demonstrations but highlights scaling difficulties, including the fragility of entangled states over distance.
Nicolas Laurent-Puig of Sorbonne University suggests near-term applications may suit small groups such as councils. Joey Marcellino of the University of Geneva indicates the method could also support secure anonymous messaging or distributed computations on untrusted quantum machines.
Journal Reference: Physical Review Letters DOI: 10.1103/jlvb-t2x1
