Soon after publishing last week’s post explaining quantum computing, the Financial Times published a story with news that Google claims to have achieved a major milestone known as quantum supremacy. This relatively straightforward concept has an intimidating name, and for the past few days the online blockchain community has been buzzing with speculation about what this means for the future of cryptography, so we wanted to briefly address this news.

#### What is Quantum Supremacy?

Quantum supremacy refers to the ability of a quantum computer to solve a
problem that a binary computer is unable to solve in a practical amount of
time. Up to the present, quantum computers have contained a small number of
qubits, limiting what they are able to compute. However, since a quantum
computer with X qubits can be in a
superposition
of up to 2^{x} states simultaneously, they have the potential to run
algorithms at speeds exponentially faster than binary computers.

This is apparently what Google researchers have been able to accomplish. While their work has not yet been published, the news report claims that the researchers used a 53-qubit computer to prove that a randomly-generated number was truly random. Their quantum computer completed this calculation in three minutes and 20 seconds, a task that would have taken a binary supercomputer 10,000 years to complete.

#### Is Cryptography Doomed?

While some commentators have been quick to welcome our new quantum computing overlords , the short-term implications of this breakthrough are modest. The task seems tailored to favor the strengths of quantum computers, rather than doing work useful for cryptographic calculations. Additional breakthroughs will be needed before quantum computing can be applied to decryption.

This doesn’t mean that the blockchain community should ignore these developments. In our next post we will describe how future quantum computers could be used to break many cryptographic systems in wide use today, and what can be done to protect cryptographic systems like blockchains.

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