They rehearse «quantum money» that cannot be falsified

Science magazine published an advance on one of the most unique ideas of current cryptography: «quantum money.»

The study was conducted by a team of researchers from the Kastler Brossel laboratory at the University of La Sorbonne, Paris, France, and released on September 19.

That group of scientists demonstrated experimentally that it is possible Integrate quantum optical memories into a cryptographic protocol which follows a quantum money scheme originally proposed by Stephen Wiesner in the 80s.

In other words, what was verified is The possibility of creating quantum tokensstore them, recover them, and verify their authenticity, with a quantum memory as an intermediate piece.

Quantum tokens are digital representations that They contain information encoded in quantum stateslike the polarization of photons.

Its main characteristic is that They cannot be cloned Due to the «non -cloning theorem» of quantum mechanics, which makes them ideal for authentication and security applications.

And where does the concept of «quantum money» enter?

Quantum money can be understood as A specialized form of those quantum tokens.

What the experiment showed is that these tokens can be generated, temporarily stored in a quantum memory, and then precisely verifiedwithout losing its quantum properties.

This represents an important step towards the practical implementation of quantum money, since it allows these “tickets” (tokens) quantum to be transportable and verifiable, maintaining its uniqueness and resistance to falsification.

Quantum money is as if physical tickets had a special ink that, trying to copy them, decomposes or changes color, revealing falsification.

In the quantum version, that ink is represented by particles such as photons: its status cannot be cloned or measured without altering it. In practice, this makes it impossible to generate an identical copy, and makes this type of token something unique.

The role of quantum memory was key to demonstrate that the complete process can be executed under verifiable security criteria.

From the theory to the experiment

Experimental work relied on three fundamental steps.

First, very weak pulses of light were used, something like small faint flashes composed of few photons whose polarization (the direction in which the light wave vibrates) was used for Codify quantum information.

That polarization functions as a microscopic lock: defines such delicate states that, when trying to copy them, They inevitably alter.

An alteration would allow to detect intruders. If an attacker measures or tries to clone a polarized photon, the state is disturbed, and the change detectable ensures the integrity of communicationa pillar of safe quantum computing.

In a second phase, these states were stored in what the study describes as an «optical quantum memory.» Imagine a kind of safe made of neutral atoms, laser cooled until almost motionless.

Being as cold, atoms behave as calm leaves in a pond, ready to record the minimum movements that They represent quantum information (those states of light that carry the coded data).

Any interference would ruin the message, but that technology, according to the report, reached almost 100% efficiency and produced «very low noise levels.»

Finally, the stored states were recovered and verified under «strict security measures.»

That quantum memory will fulfill that role without deteriorating the message is, according to the authors, what marks The difference against previous essays.

In previous studies, the storage stage was minimal or non -existent; On the other hand, this time it worked as the tangible link of a chain that Before you could only imagine in theory.

The following image represents a scheme that illustrates how optical and electronic technologies are integrated to implement advanced quantum protocols, such as those that could be used in quantum money or safe authentication:

An advance with broader implications

According to a specialized environment, the relevant thing is that quantum memory ceased to be a theoretical abstraction To become a viable tool.

Many proposals for quantum money started from the premise that states could be stored indefinitely or in ideal conditions.

The French experiment demonstrates that memories reached a level of efficiency and stability that would enable real uses.

The complete chain (creation, storage, recovery and verification) is another of the points highlighted. Having demonstrated that sequence into a controlled environment makes what Before it was only theory in a possible component of practical systems.

In addition to quantum money, optical memories open the door to other applications: repeaters for long -distance quantum communication, accurate synchronization of networks or distributed processing.

What is missing in front

Although it is an important step, the study also recognizes limitations.

The experiments were carried out with states relatively simple and under controlled conditions.

For broader applications, it would be necessary to climb in efficiency, storage times and robustness against external disturbances.

The report indicates that, even with good results, quantum devices are not free of noise and losses. Those margins, in less controlled environments, could allow verification or vulnerabilities errors.

To this is added the need for sophisticated infrastructure: photons sources, precise optics, advanced detectors and stable quantum memories, Technologies that are not yet available extended or at low cost.

Finally, the verification raises an additional challenge. Wiesner’s original scheme depended on a central authority with the ability to validate tokens.

For a quantum money system to work more openly and decentralizedly, such as Bitcoin, it would be necessary to design Verification methods accessible to multiple actorswithout relying on a single issuer.

The presented experiment also has the limitation of being supported by a centralized tokens verification model.