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While it is widely perceived that quantum computers pose a danger to Bitcoin, do quantum miners have an edge over traditional miners? If so, does Bitcoin under threat?

Will a quantum computer one day appear and use its greater computational capacity to mine away all Bitcoin and empty all wallets? While some believe this could happen in the long run, others disagree, claiming that there is no fear for a very long time.

Let us discuss a paper, in which two Canadian computer science professors analyze if there is a threat posed by quantum miners and, if so, what it is.

The way forward

The following idea serves as the foundation around which the writers formulate their question: if a miner grows too strong, the network may be in danger. He can drive 51% of the attacks if he has an absolute majority, but even if he doesn't, he may still inflict harm by engaging in "aggressive" or "selfish" mining.

What happens, then, if a miner utilizes quantum computing to such an extent that his part of the hashrate increases disproportionately?

All of this is really basic and has happened before: mining progress is accelerated by technological advancement.

It frequently happens quickly rather than gradually.

Leading processors were replaced by graphics cards starting in 2011, and Asics stopped making graphics cards in 2013.

During these times, efficiency grows quadratically or exponentially rather than linearly.

Since conventional processors have mostly reached their limits, quantum computers may represent the next big step.

This should not be an issue on its own as the game-theoretic principles of bitcoin encourage rational players to be trustworthy and keep one another in line.

However, a technological leap can be challenging, and it can open doors for adversarial forces working irrationally to undermine Bitcoin.

Knowing when it could occur makes sense, therefore.

What must occur for traditional Asics to be replaced by quantum computers in Bitcoin mining?

Unsorted database search

It is possible to see miners creating much using their computational power when discussing bitcoin mining.

They produce random hashes, and if a hash satisfies a set of standards for scarceness, the miner discovers a block.

Another term for it would be a brute force assault against the SHA256 hash algorithm.

The miners are attempting to partially reverse a cryptographic hash function, according to the two professors.

It is "equivalent to looking for a marked item in an unordered list of things (an unstructured search)" to do this "partial inversion of a hash function."

Although it seems like a small issue, everything else depends on it.

Since quantum computers are limited in what they can achieve, finding a specific item in an unordered list is one of the few tasks where quantum computers have been shown to be superior to conventional computers.

A traditional computer has to go through each entry one at a time while conducting a brute force attack or scanning an unsorted database.

It may be compared to a two-dimensional pointer that navigates between objects.

The likelihood of a hit approaches 50% once it has viewed half of the entries.

A traditional computer, therefore, requires, on average, N/2 operations, where N is the total number of objects that may be processed.

The benefit of quantum computers is as follows: Multiple qubits can concurrently represent all conceivable variations since a qubit can be both 0 and 1.

It may be compared to a pointer that points in N dimensions. The answer is already there in the qubits if they are in this "superposition."

However, as soon as you measure, the solution is ruined.

This is the infamous quantum paradox: if you count, you compel the quanta to take on a certain but random state.

The quantum computer, therefore, knows the answer, but in a cruel twist, when you go to pick it up, it devalues it.

Grover's formula squares realistic acceleration

Grover's algorithm, which was created by Lov Grover in 1996, is a technique for verifying the outcome.

The qubits identify false results and inhibit them by combining several "quantum gates," which are the operations of quantum computers.

With each iteration, or so-called Grover iteration, the likelihood of reaching the right answer rises.

The level of complexity throughout is huge.

But one thing is certain: the Grover method may significantly speed up such searches if the right amount of repetitions is used.

Grover only requires n tries to locate a particular item in an unsorted list.

As a result, it is almost four times quicker.

Two instances: Both conventional and quantum computers need two trials if there are four objects.

In contrast, a quantum computer is discovered after 2280 attempts when there are 5,198,400 pieces, but a normal computer must run more than two million times.

This difference is significant, particularly for activities with a very high N or that is highly tough. The so-called quantum advantage is this difference.

One of those jumps that may completely upend an ecosystem. at least conceptually.

Quantum advantage is disappearing

In actuality, a quantum miner encounters a specific issue: He cannot locate a block until he gauges the outcome, which forces him to halt the operation.

He must thus plan how many iterations he will perform in advance.

The query is challenging. because there are drawbacks to both having too many and too few.

More iterations raise the danger that another miner will be quicker and the likelihood that the correct answer will be found.

Conversely, fewer repetitions reduce the likelihood of a legitimate result and, as a result, the quantum advantage.

A quantum computer might fully utilize the quantum advantage if it had infinite time. However, mining prohibits this. Between too few and too many iterations, a balance must be struck.

The researchers created a Markov chain containing all of the potential outcomes in order to determine the best trade-off.

A mathematical representation of potential, largely random, or partially unexpected sequences is called a Markov chain.

Such a chain shows which route through the maze of probability, or the best Grover algorithm configuration, often lead to the best outcomes.

This would take, astonishingly, 16 minutes.

Two outstanding discoveries

Let's say it takes a quantum miner 16 minutes to read Grover's algorithm's output. When compared to the long-term drawbacks, its benefit over traditional mining is at its greatest.

The scientists assert that this benefit is there regardless of the challenge.

Because it can be used, the outcome is quite impressive. Here, two grave outcomes may be seen:

First off, by using such a strategy, the miner excludes himself from around 80% of the blocks. This is a result of things being discovered in under 16 minutes.

With the remaining 20%, he increases his chances of success.

The overall mining power that quantum computers should be able to reach should not exceed this without compromising effectiveness.

Second, the time between blocks is often shorter for cryptocurrencies. Ethereum and Ripple only have a few seconds, whereas Dogecoin and Litecoin have a few minutes.

With these blockchains, the quantum advantage doesn't hold true, hence quantum miners are suffering a bloody nose. In mining, they are already quantum-safe.

Quantum computer parallelization likewise appears to be a dead end.

The Grover method makes this conceivable, however, the authors' calculations show that it only enhances performance by a factor of m.

The element is m for traditional computers, making it quadratically bigger.

It is therefore doubtful that quantum computers would ever be useful for mining.

Megahashes: 78

Already, these computations significantly lessen the threat posed by quantum computers.

But the most important query is still unanswered: What must occur before quantum miners have the upper hand over traditional miners?

When, if ever, will use a quantum computer to discover a block become less expensive?

The cost per grover iteration and the proportion of hashes needed for a block to grover iterations needed are the two determining elements in this.

The authors do this calculation using the example of a quantum computer that is currently prevalent and has a "gate speed" of 66.7 MegaHertz.

The gates, or quantum processes, are the gates.

According to the researchers' calculations, this quantum computer could perform 224 Grovers every second.

Meaning? A hashrate of 78 mega hashes per second is equivalent to 224 Grover iterations.

That amounts to a minuscule portion of the Bitcoin hashrate and is far less than what is accomplished by contemporary Asics. It would be absurd to perceive any threat here.

Possibly future versions that are more energy-efficient

But are quantum miners at least more productive if they don't represent a threat? So, is it possible to transition to quantum mining, if only gradually? Additionally, when?

The energy cost of a Grover iteration should only be 3.49 × 105 times that of a conventional hash in order to be more effective.

A quantum computer would need an efficiency better than 3.49 x 105 × 10-10, or around ten J every Grover iteration, in order to be as energy-efficient as traditional miners, which have an energy efficiency of 10-10 Jules per hash, perhaps even 2240 J/s.

That seems really demeaning. However, quantum computers need relatively little energy.

The quantum bits transform into a superconductor after the system is cooled to 15 millikelvins, or almost absolute zero, and need almost little electricity and generate almost no heat.

A quantum computer is still uneconomical at the moment because of cooling in relation to electricity.

But as technology develops, this should change.

In conclusion, Bitcoin users should rest easy knowing they are a little smarter and can no longer imagine the terror of a world run by quantum computers.

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