**español**

China is getting ahead of the U.S. in the quantum race. Last week, it announced beating Google’s most advanced quantum computer. Meanwhile, IBM began installing a major quantum computer development project in Germany, announced to great fanfare by the German government, which it claims will generate €75 billion of “value.” The imperialist conflict is being played out in several fields at once. Information technologies and in particular the quantum race are among the main ones.

## Table of Contents

- The quantum race: a new version of the space race?
- A basic introduction
- Cryptography and the quantum race
- How does one build a quantum computer
- Quantum encryption and capital’s control over communications

## The quantum race: a new version of the space race?

One of the first aspects highlighted by the media about this technological race between powers is its similarity to the cold war space race:

Tensions between the US and China are currently at their highest point in decades, with the countries at odds over trade, human rights, spying concerns, COVID and Taiwan. Following China’s demonstration of the Mozi satellite [墨子] in 2017, U.S. policymakers responded by committing hundreds of millions of dollars to quantum information science through the National Quantum Initiative. It was eerie déjà vu. Some 60 years earlier, the U.S. was pushed into funding another major initiative – space exploration – by fears over a small Soviet satellite called Sputnik.

And they’re really not misguided, in fact, quantum computing projects and space plans – from which they tried to kick Switzerland, UK and Israel out recently – are tied together for the EU, and in the US NASA technicians are the ones leading the quantum race. But what is so special about quantum computing to arouse the interest of so many world powers and attract so much investment? It’s all based on the somewhat bizarre characteristics of matter on an incredibly small scale.

## A basic introduction

In a classical digital computer, logical operations are based on binary states: 0 or 1 and, at first glance, this is also the case in the particle systems used by a quantum computer.

An electron, for instance, can be found on measurement in 2 possible states, which are known as *spin* up or down. This is how they are found surrounding the nucleus of atoms, each *orbital* composed of pairs of electrons of opposite spin.

However, experimental results were at odds with this well-ordered explanation of the microscopic world. Although particles are always found to be spin up or spin down at the time of measurement, outside of that time their behavior is more like a mixture of both extreme states, commonly referred to as a superposition state.

One of the possible ways to represent this brainteaser was to set aside the mathematical methods of classical mechanics and adopt as representation vector systems and special geometries.

A simple geometric representation is generally used to explain quantum phenomena and the operations of quantum computers. The two mutually exclusive states are represented at opposite poles of a circle of radius 1 and their superposition is represented as an arbitrary point on this circumference (figure A in the graphic below).

So, **any point can be represented as the (vector) combination of both states** multiplied by a coefficient each (in the case of a quantum system, these coefficients represent the probability that, when measured, the system is spin up or spin down). One consequence jumps out immediately, and it is one of the main advantages of quantum computing: **there are infinitely many points on the circumference and the system could perform immense computations in parallel through superposition**.

In reality, quantum states cannot be represented using the normal – Euclidean – geometry, and a special extension of geometry must be used which entails replacing our circle with a sphere, the Bloch sphere. The sphere works just like the circle, and the quantum states are represented as dots on its surface.

Thus, the overlapping, superposed, states of the particles manipulated by quantum computers are represented graphically as vectors pointing to points on a sphere, and all the logic gates used by quantum computers are based on changes of the superposition state amounting to translations of those points on the sphere (as can be seen in figure 1c).

## Cryptography and the quantum race

What is the point of all this theoretical development? One of the quantum applications that the military is most interested in can be explained using what we have already laid out.

A single pair of states (vectors) is enough to generate all the points on the circle and this pair is called a **basis**. In particles that are used to send signals, such as photons, a plethora of different bases can be used in order to encode the signal by superposing the states when sending the particle. The important thing is that in order to *read* correctly a particle sent as a signal to a receiver one must know on which basis the information has been encoded, otherwise one ends up getting a completely random result.

On this same principle are based a number of famous quantum encryption protocols which allow information to be sent between two agents. The first agent encrypting the signals by using random bases and then communicating part of the used bases to the receiver only *after* the latter receives all the photons.

In these protocols any interference or eavesdropping is immediately detected and impossible to hide. Any eavesdropper needs to interact with the particles on the line in order to *listen* to the conversation, but in doing so the superposition of states disappears or is affected and — not knowing in advance the basis on which each particle was encrypted — necessarily skews the results expected by the receiver had no one been eavesdropping on the line.

The first goal of the research groups in the quantum race is cryptographic: making communications foolproof against rival interception and encryption systems.

## How does one build a quantum computer

The usefulness – at least for the military – of the quantum race is clear. And it all comes down to creating a system able to manipulate the quantum states of particles. But the way to build a device capable of doing so is quite a different matter.

Classical computers do not manipulate individual electrons, and doing so with quantum computers is extremely complicated. It would be convenient to be able to get a *megaparticle* that is both easily manipulated and stable in a circuit in order to play with it through physical trickery. That’s exactly what several of the most powerful quantum computers such as those from IBM do.

We said earlier that electrons *cannot bear* finding themselves in groups of more than two for the same energy level, as when they form the *ordered orbitals* of atoms or move freely in a disordered cloud form. In reality this is only half true.

If we sharply lower the temperature to near absolute 0, the free electrons circulating in a metal completely change their behavior, they all come together on the same energy level and start to behave like a huge megaparticle in what is known as superconductivity.

Using the same tools employed for silicon chips and by carefully microprinting bridges and junctions (see Figure 2 a,b) a quantum system can be constructed that is the equivalent of a system with a single electron and two states but on a much larger and manipulable scale.

These **qubits** (quantum bits) possess two quantum states that can be superimposed like those of an electron due to the microwave pulses sent by the logic gates (XYZ in the figure, they refer to rotations around the axes of the Bloch sphere).

But the true power of a quantum computer is not based on the capacity of an individual qubit. Yes, it is true that a single qubit can be in a superposition with huge values, but when measured all information is lost and it reverts to 0 or 1.

Quantum *algorithms* are the real strength of a quantum computer, and are based on making several qubits interact with each other, in order to indirectly read the parallel operations being performed by some qubits through the measurement of other qubits which are interfering with them.

By putting a bunch of qubits in parallel (Figure 3a ), several of the functions that so fascinate the military can be carried out. By controlling which gates apply to which qubits over time and which qubits interfere with each other, one can manage to use the power of state superposition on some qubits to perform a lot of operations in parallel, such as breaking military ciphers based on logarithms or large prime numbers.

Also, somewhat more useful to the fulfillment of human needs, it can for instance also be used to compute the similarity between two graphs by simultaneously computing all the paths (Figure 3b).

## Quantum encryption and capital’s control over communications

However, as attractive as it is to break foreign codes, the main military and commercial interest in the quantum race does not lie in quantum computers per se. In fact, there have always been doubts about their real usefulness, since **the number of algorithms in which they show a real advantage over classical computers is very small and they have little applicability for most problems**. Current quantum computers are light years away from a classical computer.

These algorithms may fascinate physicists and computer theorists, but they do not outweigh either the enormous cost of maintaining the hardware at minuscule temperatures or their manufacturing cost. The interest of the quantum race for capital lies elsewhere.

Using hardware similar to that of algorithms and using another surprising property of quantum mechanics – entanglement – a state can be distributed among several entangled particles, making them able to be used to communicate instantaneously. These are the *ultrasecure quantum keys* so much talked about today in all things related to the quantum race.

When one of the two (or more) entangled particles is measured, it loses its superposition of states and reverts to 0 or 1 as expected, but the interesting thing is that the other particle is also affected instantaneously and independently of distance and without anything having been sent between the two. This is the dream of communication that is impossible to intercept, and it is in this respect that the Chinese have a big advantage in the quantum race.

Combining what we have seen so far with this new aspect, the most advanced protocols suggest using a series of logic gates to – in a similar way to the interference we saw above – partition the quantum state among different particles and send them to different agents (Figure 4b).

And this is where capital really gets excited in the throes of an investment orgy: it dreams of being able to centralize the distribution of these keys for a ” new quantum internet” into the hands of a few capitals able to afford the investments and technology:

A complete quantum network aspires to more. It would not be limited to transmitting entangled particles, but would “distribute entanglement as a resource,” says Neil Zimmerman, a physicist at the National Institute of Standards and Technology, allowing devices to be entangled for long periods, sharing and exploiting quantum information. […]

Taking this idea further, some also envision an analog of cloud computing: so-called blind quantum computing. The idea is that the most powerful quantum computers will one day be located in national laboratories, universities and companies, just like today’s supercomputers.

What lies beneath the quantum race is clear: the whole range from military uses to the creation of a new investment field for large capitals with currently find themselves devoid of profitable placements. On the way: the prospect of even greater concentration of communications control. In a word: imperialism.

The quantum race is one more proof that the today’s capitalism, far from satisfying more human needs and producing real human development, only knows how to create even more scarcity and deform in its own interest all the developments and advances of social knowledge.

**español**

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