The First Modem For The Quantum Internet Is Now A Reality

Quantum Dec 21, 2020

Twenty-two years since the creation of the first quantum computer, and only one since the first quantum computer for commercial use, the quantum internet has come to connect these devices in an ultrasecure, ultrafast, and ultra powerful way.

What is the Quantum Internet?

To be able to understand what the quantum internet is, we need to keep in mind the principal characteristic of quantum computation, which is that it utilizes as its basic unit of information the qubit instead of a bit. While a bit in classical computers is the basis for the binary system, named that way because it can only have the value 1 or 0, a qubit is a quantum bit that can have both values at the same time. That is to say, the qubit permits the superposition of both states, which opens new logical gates for new algorithms, and gives way to new quantum circuits that can comprise a network. The result of this network is a greater capacity for calculation and simultaneous operations at a higher velocity.

The quantum internet, therefore, is a global network of quantum communication in which quantum information is transmitted in the form of qubits by way of distinct remote quantum devices. As simple - almost redundant - as it sounds, in practice it is a little more complicated because of this question: How does one transmit quantum information at great distances without its deterioration?

In today’s day and age, it is commonly known that light is an ideal way for transmitting information, by way of the high speed at which it travels (299,792,458 meters per second). It is key, for instance, for communication in outer space, one of the most complicated forms of communication because of distance and interferences caused by radiation.

Quantum internet also uses light. It becomes utilized between stationary qubits (those that are in a precise local unit) and “flying” qubits, which are nothing more and nothing less than quanta (a quantum being the smallest quantity of radiant energy) of light that carry information.


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But until now there was no medium of transmission for this. The information contained in the light is highly sensitive, because it is of quite a volatile signal, prone to degrade in the air. One proposal, for this reason, was that the quantum internet be developed in a place where there is no air: in space. Meaning, by way of satellites. The problem was that it was an option too costly.

That was where the protagonist of this story entered in: the quantum modem.

The Quantum Modem

We owe advances in this area to Quantum Networks, the Otto-Hahn group at the Max-Planck-Institute of Quantum Optics in Garching Bei München, Germany. There, the team led by researcher Andreas Reiserer developed the first prototype of a quantum modem, using basic albeit effective technology. It is therefore capable of connecting stationary qubits with flying qubits using networks of optical fiber (the optical fiber already in use today). All of this is to say that, thanks to this modem, we will not need anything “new” to connect to a quantum internet of the future, which seems to be an efficient way towards reaching that day.

But, how does it work, exactly? The modem receives and sends the quanta of light that contain the information in the same line of the infrared wavelength of the light of a laser (which is the very “essence” of fiber optics) across qubits at rest that react to the light and realize a “quantum leap”.

To achieve this, the electrons of the element erbium are ideal, but they need to be forced to simultaneously coexist with the infrared light in such a small amount of space that is able to compensate for the volatility of the photons. Because of this, the team at the Max-Planck-Institute of Quantum Optics opted for a transparent crystal of yttrium silicate, five times finer than a human hair, as well as mirrors that make the photons “bounce” to help them make the leap. These mirrors are at the same time permeable enough to absorb the photons necessary to allow for the execution of the back and forth of information, which is fundamental to an internet connection.

All of this takes place at a temperature similar to that of the rest of the components of a quantum computer: approximately 270 degrees below zero Celsius. Thermal oscillation of the atoms could, of course, destroy the quantum information, therefore cooling techniques are applied.

What Can We Expect For The Future?

This technology can allow for, later on, erbium atoms to arrive as qubits individually by way of the light of a laser. These, contained within a crystal, could act as a quantum processor, to increase the compatibility of the modem with quantum terminals.

After this, quantum repeaters can be developed that, being installed every certain number of kilometers, would aim to minimize the loss of quantum information (remember that the information would be in photons in fiber optic networks) across wide distances. This would be quite expensive to begin with, but not entirely impossible.


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