Searching for "MOSS" in the real world (Part 1): Is such a large computing power really possible?

Produced by: Science Popularization China

Author: Luan Chunyang (Department of Physics, Tsinghua University)

Producer: China Science Expo

The popular sci-fi movie "The Wandering Earth 2" has ignited people's infinite imagination of future technology. This movie, set in the 2040s, features a series of "black technologies" - from data centers submerged in the deep sea, to "planetary engines" that propel the Earth to wander, and "digital life" with autonomous consciousness. Behind these "black technologies" in the movie, there is always the figure of the "intelligent quantum computer 550W" (MOSS).

Relying on the exponential computing power of quantum computers, "MOSS" can not only integrate and dispatch computing resources around the world to meet the coordinated operation of 10,000 "planetary engines" around the world, but also meet the massive computing power requirements of the "Digital Life Project", which can be said to have satisfied everyone's infinite imagination of future quantum computers.

MOSS in "The Wandering Earth 2"

(Photo source: Stills from "The Wandering Earth 2")

When dreams become reality: Finding "MOSS" in the real world

So imagine that if we want to refer to the "MOSS" setting in "The Wandering Earth 2" to build a real quantum computer, we need to review the performance description of "MOSS" in the movie.

First of all, "MOSS" is the latest quantum computer in the "550" series and is the core intelligent host of the Navigator Space Station; secondly, although the interactive terminal of "MOSS" can work at normal temperature and pressure, a huge refrigeration device has always been connected to "MOSS" during the development process; finally, according to the self-introduction of "MOSS" in the movie, its computing power is measured by the new indicator of "quantum volume", and it is precisely with the super computing power of 8192 "quantum volumes" that it can make the most correct decision in the shortest time, thereby firmly executing the mission of continuing human civilization.

(Photo source: Veer Gallery)

Since science fiction movies are derived from science and technology in the real world, we can first find some clues about "MOSS" in the development of today's quantum computers based on the important clue of "8192 quantum volumes", so as to turn the dream of building a quantum computer into reality.

“Quantum volume” – a metric for evaluating the overall performance of quantum computers

The computing devices we usually come into contact with are all classical computers, which use binary operations of 1 and 0, and this basic operation unit that can only represent the 1 state or the 0 state is called a "bit". In the data operation of quantum computers, the basic operation unit can not only represent the 1 state or the 0 state, but also can probabilistically exist in the 1 state and the 0 state at the same time. This basic operation unit that can represent the entangled state of 1 and 0 is called a "quantum bit".

Therefore, the most fundamental difference between quantum computers and classical computers is that quantum computers can perform parallel calculations by relying on the magical power of "quantum bits" in an entangled state of 1 and 0, thereby obtaining exponentially high computing power.

(Photo source: Veer Gallery)

Scientists have also gradually discovered physical carriers that can serve as "quantum bits", including charged ions, neutral atoms, light quanta that exist naturally in nature, as well as artificial "superconducting quanta" and quantum dots, and have developed different implementation plans for quantum computers from this.

However, different implementations have their own advantages and disadvantages, which requires a unified standard to evaluate the overall performance of different types of quantum computers. This is just like in daily life, if you want to compare the overall performance of processors produced by different electronics manufacturers, you need to use a unified standard evaluation algorithm for running tests. For different types of quantum computers, this scientific indicator for evaluating overall computing performance is called "quantum volume" (QV).

Schematic diagram of the quantum computer chip developed by IBM

Image source: IBM

Specifically, "quantum volume" is not a volume concept in geometric mathematics, but a set of statistical tests involving multiple factors and complex calculations. There are three main components: the number of quantum bits, the comprehensive error rate of calculations, and the connectivity of quantum bits.

Ideally, if a quantum computer has N qubits for parallel computing, it can theoretically achieve a computing power of 2 to the power of N. The ideal is beautiful, but the reality is complicated. In reality, there is always a certain amount of environmental interference, so there is always a certain comprehensive error rate in the calculation of quantum computers. In order to compensate for this part of the loss, quantum computers need an additional number of qubits in actual calculations.

In addition, for a quantum computer with N qubits, any two qubits need to be able to be interconnected through "quantum entanglement" in order to complete the parallel operation of N qubits. However, due to the architectural design of different models of quantum computers, qubits in some implementations can only be interconnected with the nearest neighbor qubits, which reduces the connectivity of qubits and greatly reduces the originally ideal exponential computing power.

The architecture of the 20-qubit and 50-qubit chips developed by IBM shows that each quantum can only connect to adjacent quantum bits.

(Image source: IBM)

Imagine if there were three different types of quantum computers:

1) A type quantum computer has 12 qubits, but each qubit has a certain operational error rate, and each qubit can only be connected to its nearest neighbor;

2) Type B quantum computers have 8 perfect qubits, and each qubit can only be connected to its nearest neighbors;

3) Although the C-type quantum computer has only 5 perfect quantum bits, each quantum bit can be connected to each other arbitrarily.

In this way, we can comprehensively consider the number of quantum bits, the overall error rate of calculations, and the connectivity of quantum bits, and use the overall indicator of "quantum volume" to evaluate the overall performance of the three different models of quantum computers, ABC.

(Image source: self-made by the author)

Continue to evolve and continuously refresh the "quantum volume"

Quantum computers are evolving at a rate that at least doubles their quantum volume every year since the concept of "quantum volume" was first proposed in 2017. This is similar to Moore's Law, which describes the continuous iteration of classical computers, that is, the computing power of classical computers doubles approximately every two years.

As early as 2017, the research team had achieved 4 quantum volumes (QV4) using 5 quantum bits; in 2018 and 2019, the research team further used 20 quantum bits to increase to 8 quantum volumes (QV8) and 16 quantum volumes (QV16), respectively. In the following 2020 and 2021, the quantum volume was further refreshed to QV128 and QV2048. In 2022, a quantum computer based on the ion trap experimental scheme set a new record of 8192 quantum volumes (QV8192) with its extremely low calculation error rate...

Quantum volume will reach 8192 in 2022

(Image source: Quantinuum)

It can be seen that the parameter setting of "MOSS" in the movie is very likely derived from the latest quantum computer in reality, but "8192 quantum volumes" is still at a very initial development level, and it is probably far from reaching the super computing power of "MOSS" in the movie. Scientists predict that with the continuous upgrading of quantum computers, it is believed that in the near future, quantum computers will reach millions of quantum volumes, thus eventually realizing universal quantum computers.

The next-generation quantum computer developed by IBM has an internal chip called Osprey with 433 qubits.

(Image source: IBM)

Now we look back at the "MOSS" in the movie, and we can't help but start to think again: Why was a huge refrigeration device always connected during the development of "MOSS"? Does the ion trap quantum computer that set the latest quantum volume record in reality use the same technical solution as "MOSS"? Since quantum computers are easily disturbed by the external environment, why can the interactive terminal of "MOSS" work at room temperature and pressure? If you want to know the answer to the question, we will continue to introduce the real prototypes of "MOSS" in the next article - superconducting quantum bit solution, ion trap quantum bit solution and optical quantum bit solution.