Google's 72-bit quantum computer, is Bitcoin still safe?

At this year’s annual meeting of the American Physical Society in Los Angeles, Google made a big move and released Bristlecon, the world’s first 72-bit universal quantum computer, achieving a low error rate of 1%, which is similar to what Google had previously involved. A 9-qubit universal quantum computer is flat. This processor can not only help scientists explore quantum simulations, but also have applications in quantum optimization and quantum machine learning.

Relevant personnel from Google stated:

We are cautiously and optimistically convinced that Bristlecone can achieve quantum supremacy (Quantum Supremacy).

Google's latest quantum processor Bristlecon

Regarding this quantum computer, we can understand the following concepts:

Quantum Supremacy

"Quantum supremacy" is also known as "quantum superiority," a term that relates to the ability of quantum computers to surpass classical supercomputers on certain types of equations. Specifically, a 50-qubit quantum computer is better than any classical computer currently available. Only when quantum supremacy is achieved can a quantum computer be considered a real quantum computer. However, the metric used to measure the performance of a quantum processor to determine whether quantum supremacy has been achieved is also a source of debate among quantum physicists.

It is well known that the computing power of quantum computers greatly exceeds the capabilities of the most advanced supercomputers. Some experts believe that this can be said to be a big step in the development of quantum chips. Quantum particles are arranged in a two-dimensional layout, making the control system more complex. This is closer to what is needed to achieve surface coding, the ability to manipulate quanta in a quantum system to perform useful calculations. Relevant Google staff believe that the new processor released this time will not only achieve quantum hegemony, but Google has developed a benchmark tool to measure whether quantum computers have reached the standard of quantum hegemony. This test applies random individual quantum circuits to a processor and measures the output of a classical simulation.

Bristlecone

This computer was developed by Google Quantum AI lab and is based on a nine-bit matrix developed by Google researchers. It resembles the shape of a pine cone, hence its name. For Bristlecone (bristlecone pine). The goal of Google's Quantum AI Lab is to build quantum computers that can be used to solve real-world problems. Their research strategy is to explore short-term solutions on systems that are forward compatible with large-scale, general-purpose, error-correctable quantum computers. .

Schematic diagram of the chip structure, each "X" represents a qubit, and the nearest adjacent qubits are connected

In order to allow the quantum processor to run Algorithms other than classical simulation algorithms certainly require more qubits (qubits), but it also requires more. Crucially, the processor must maintain low error rates in reading and logic operations such as single- and dual-qubit gates.

Qubits

Qubits are a quantum analog form of digital bits and are the smallest units of information processed by traditional computers. However, digital bits are binary and can only choose between 0 and 1. And qubits can exist in superpositions of states (their values ​​can be 0, 1, or other combinations). If there are N qubits, 2^N data can theoretically be stored at the same time. For example, the data that can be stored by 250 qubits is 2^250, which is more than all the atoms in the known universe combined. When a quantum computer performs operations, it can calculate 2^N mathematical operations at the same time, which is equivalent to a classical computer repeating 2^N calculations. It can be seen that quantum computers can save a lot of time and computing units, allowing quantum computers to query databases, decompose large prime numbers or create complex scientific models, and are more efficient and accurate than supercomputers.

Number of Qubits

But creating a large-scale quantum computer is more than just stringing a bunch of qubits together. Creating qubit arrays is a challenging task. Special materials are often required, expensive laser setups and/or extreme environmental conditions are required to successfully create and function properly, depending on whether the qubit is based on ions, spin semiconductors or Google processors or superconducting circuits.

It should be noted that the qubit itself is very sensitive to noise environmental interference. Non-ideal environments may cause problems with the state of the qubit, so it is very error-prone. Creating powerful qubit arrays with minimal error rates is one of the biggest obstacles between physicists and powerful quantum computers.

Error rate

Since the quantum state is very unstable, only 50 qubits are not enough, because the quantum entanglement of qubits will go wrong, and only enough qubits Only with a low error rate can true quantum supremacy be achieved.

Install Bristlecone

The qubit matrix used in this 72-bit quantum computer (similar to the previous 9-qubit universal quantum computer) is capable of achieving a 1% read error rate, a 0.1% single-qubit gate error rate, and a 0.6% double-qubit gate error rate. Bit gate error rate. Qubit gates are quantum gates (also called quantum logic) that are basic and operate a quantum circuit with a small number of qubits. It is the basis of quantum circuits, just like the relationship between traditional logic gates and general digital circuits. Common quantum gates perform logical operations on one or two qubits, ultimately producing a single output.

Quantum computers may crack Bitcoin

Currently quantum computers are only used in the field of scientific research, but if, as Google Labs says, Bristlecone can achieve quantum hegemony, then Bitcoin and other areas based on The virtual currency of blockchain technology may be cracked.

According to the principle of majority rule in the blockchain, once a miner owns 51% of the computing power, other subsequent miners will not be able to continue to obtain Bitcoins. In the future, as the number of qubits in quantum computers increases, the asymmetric cryptography algorithm used in the blockchain, that is, the public key cryptosystem, will also be under greater threat.

By using a quantum computer, the process of using the public key to infer the private key can be reversed, and everyone's private key will be easily inferred by the quantum computer. Foreign media Motherboard believes that a 4,000-qubit quantum computer can disrupt the blockchain. In other words, whichever person or team first develops and applies such a quantum computer can solve and verify every transaction, and there will be more in the future. All cryptocurrencies that are not in circulation will be monopolized by it, and the trust system of cryptocurrencies will be destroyed. For details, please see FreeBuf’s special article: Quantum computing moves from concept to reality, is public key encryption in danger?

Strictly speaking, the advent of quantum computers will threaten all cryptography of the existing system and will rewrite the security protection of the entire financial and banking industry.

However, many scientists believe that quantum computers cannot replace classical computers. Because the computing characteristics of quantum computers determine that they can only be used in a small number of fields, the working scope of classical computers far exceeds that of quantum computers.

However, all blockchain technology developers should also be more vigilant. The release of Google’s quantum computer indicates that there may be earth-shaking changes in the future blockchain field.