The Chinese quantum computer Jiuzhang announced to the world

About a year after Google's announcement on the achievement of quantum "supremacy", China too reports that it has achieved this important goal. Named Jiuzhang after an ancient Chinese mathematical text, the new quantum computer can perform a calculation that would take more than half a billion years on a classical computer in just 200 seconds . This is what the Chinese researchers reported in the study published in Science last December 3.

This is a result that increases interest in photonic quantum computers, which have never received the same attention as other technologies. In fact, although these computers are able to perform operations with unparalleled speed, they are still operations of little use. The operations we are talking about concern calculations that have little to do with the applications currently used but that in the future will give the boost to areas such as computer security and artificial intelligence.

Characteristics of the Jiuzhang quantum computer

The Jiuzhang quantum computer consists of a complex series of optical devices that carry photons. These devices include light sources, hundreds of beam splitters, dozens of mirrors, and 100 photon detectors. The process used is that of boson sampling through which a distribution of numbers is generated which is extremely difficult to replicate for a classical computer.

The process starts with sending photons into a network of channels. In its path, each single photon encounters a series of ray dividers, in which it sends the photon along two paths simultaneously, in what is called a quantum superposition. Paths also blend together, and repeated splitting and merging cause photons to interfere with each other according to nondeterministic rules.

The Chinese quantum computer Jiuzhang uses a photon and channel technique to replicate what is called quantum superposition
Credit: The quantum computer developed in China uses a network of channels and photons that make it one of a kind.

Finally, the number of photons in each of the network's output channels is measured at the end. Using a large number of photons and channels, the quantum computer will produce a distribution of numbers that is impossible for a classical computer to calculate.

A limitation of Jiuzhang concerns the ability to perform only a single type of activity at a time , namely boson sampling. Conversely, Google's quantum computer could be programmed to run a variety of algorithms just as other types of photonic quantum computers are programmable as well.

Demonstrating quantum supremacy with hitherto unknown technology highlights how rapidly quantum computing is progressing.

The quantum computer

So how does a quantum computer work? The idea behind its operation concerns a revolution in information representation. In fact in quantum computers the classic 1/0 bits are not used which represent the two on / off states. The name suggests that quantum computers use the phenomena of quantum mechanics according to which subatomic particles can present themselves in multiple states at any moment . In this way, the amount of information that can be processed is far greater than what we have seen so far. The basic information unit of quantum computers is the qubit. Having n qubits available, it is therefore possible to encode to represent 2 ^ n inputs every instant. To give an example, if a bit represents the basic information unit with only two states, the qubit instead represents an infinity of states enclosed between zero, one and a certain probability value.

Representation between the values ​​assumed by a bit and the possible ones of a qubit.
Credit: The bit can only take on two values ​​0/1, for the qubit the possibilities are almost infinite.

Information is no longer considered as deterministic but as probabilistic. This result allows a quantum computer to solve in a few days, or even hours, complex problems that would take billions of years to today's computers.

Research in the field of quantum mechanics is currently evolving more and more. Until now, in fact, the only way to make the processing more efficient was to insert an increasing number of transistors on the integrated cards. However, this type of activity has a limit in Moore's law for which the complexity of a microcircuit, measured for example by the number of transistors per chip, doubles every 18 months (and therefore quadruples every 3 years). The progress of miniaturization has had to come to a halt providing impetus to this new mode of construction.

The limits of this technology are still many, from maintaining the quality of photons to the technological difficulties related to their operation in extreme conditions. This is an area of ​​research still in the launch phase that will surely affect our future. It is no coincidence that the largest IT-related companies such as Amazon, Google, Microsoft are investing in this sector. We just have to wait to find out what the future frontiers will be.

The article Announced to the world the Chinese quantum computer Jiuzhang comes from TechCuE .