The dream of a completely secure, unhackable, absolutely private digital payment system could soon be realized thanks to new research out of the University of Vienna.

In a paper published on July 4 titled “Demonstration of quantum-digital payments,” a team of researchers at the Vienna Center for Quantum Science and Technology showed off what may be the first “unconditionally secure” digital transaction system based on quantum mechanics.

To accomplish this, the researchers encrypted a payment transaction using a pair of quantum entangled photons. Through this entanglement, wherein any change in the state featured by one photon is reflected exactly in the other photon, even when separated by distance, the researchers were able to ensure that any attempts to modify the transaction are thwarted by the nature of quantum mechanics itself.

Per the researchers’ paper:

“We show how quantum light can secure daily digital payments by generating inherently unforgeable quantum cryptograms.”

One of the most useful features of quantum entanglement is the fact that we can’t know what state an entangled object is in until we measure it.

A simple way to understand quantum mechanics and measurements is to imagine flipping a coin and then catching it and covering it with your hand before you or anyone else can see what side it landed on. Until you remove your hand, it can be heads or tails with equal probability. Once measured, the uncertainty collapses and you have a measurement.

Scientists can exploit this by using entangled objects, such as photons, to ensure parity and send information that can’t be modified or intercepted.

Thus, the researchers generated entangled photons using a laser process and encoded them with transaction information. The photons were then sent through over 400 meters of fiber optic cables to successfully complete a digital payment transaction between parties in different buildings.

Were a bad actor to attempt an adversarial attack on such a transaction, the quantum state of the photons would collapse due to measurement, and the system would generate a new pair of entangled photons with a novel, unforgeable cryptogram.

While it’s possible this could represent a breakthrough in quantum communications for digital payments, there is one small caveat: Currently, the researchers say it takes “tens of minutes” for a simple digital payment to complete using the method.

However, this limitation may only be temporary, as the researchers are adamant that this isn’t a hard stop due to the laws of physics but just a minor technological limitation — one that might be resolved through higher-intensity photons.

“Indeed, brighter sources of entangled photon pairs have already been demonstrated, which could decrease the quantum token transmission time to under a second,” wrote the authors.