{"id":18999,"date":"2019-11-06T05:00:00","date_gmt":"2019-11-06T05:00:00","guid":{"rendered":"http:\/\/ci027d05d1c0002697"},"modified":"2025-01-27T21:04:14","modified_gmt":"2025-01-27T21:04:14","slug":"what-is-quantum-computing","status":"publish","type":"post","link":"https:\/\/bitcoinmagazine.com\/guides\/what-is-quantum-computing","title":{"rendered":"What Is Quantum Computing?"},"content":{"rendered":"
<\/div>
<\/figure>\n

Quantum computing is a form of computing based on quantum physics. Where classical computers rely on bits (zeros or ones) to make calculations, quantum computers use quantum bits (qubits) that leverage quantum mechanics to exist in a \u201csuperposition\u201d: a combination of zero and one, with some probability for each. A qubit could, for example, have an 80 percent chance of being zero, and a 20 percent chance of being one. Or a 60 percent chance of being zero, and a 40 percent chance of being one. And so forth.<\/p>\n

The idea of quantum computing<\/a> was first introduced by physicist Paul Benioff in the 1980s. A little later, theoretical physicist Richard Feynman and mathematician Yuri Manin were the first to suggest that quantum computers could solve problems that are out of reach for classical computers. Indeed, in the 1990s, mathematician Peter Shor developed an algorithm that a quantum computer could use to break public-key cryptography: \u201cShor\u2019s algorithm<\/a>\u201d \u2014 if quantum computers ever got strong enough.<\/p>\n

In October 2019, after decades of research, Google officially claimed that it had reached \u201cquantum supremacy.\u201d This essentially means that a quantum computer solved a problem that a classical computer could not have solved. Or, to be more specific, it solved a problem in 200 seconds that would have taken even the strongest classical supercomputer 10,000 years to solve.<\/p>\n

While this was a big breakthrough, quantum computers still seem to be a long way off from running Shor\u2019s algorithm. For one thing, current quantum computers are not nearly strong enough for this, and it\u2019s unclear how easy or hard it is to scale the technology up. Furthermore, to actually be useful, quantum computers depend on a technical solution called \u201cerror correction,\u201d and this is still a challenge as well.<\/p>\n

Predicting future development of this technology is hard, but quantum computers that can run Shor\u2019s algorithm are likely years or even decades away \u2014 perhaps they will never even be possible at all.<\/p>\n

Is Quantum Supremacy a Threat to Bitcoin?<\/h2>\n

If quantum computers get to the point where they can run Shor\u2019s algorithm and break public-key cryptography, Bitcoin could indeed be subject to attack. Specifically, a number of coins could be subject to theft.<\/p>\n

Some argue that the theft would be somewhat limited, however. While all coins are secured by public-key cryptography (currently, the ECDSA algorithm), most coins are also secured by the SHA256 hashing algorithm. Only if both of these algorithms are broken could all coins be stolen outright, but it does not currently seem as if SHA256 (or any other hashing algorithm) can be broken by quantum computers.<\/p>\n

That said, a very large amount of coins is only secured by public-key cryptography. Current estimates suggest that around 5 million bitcoin would be subject to theft if public-key cryptography were broken. These are some of the situations in which bitcoin may be at risk:<\/p>\n