Building a quantum computer. Qubit on atom

Scientists around the world are striving to build a quantum computer. A computer naturally requires a storage medium. They called it a qubit - a quantum bit. But what the physical carrier of this qubit should be is not yet determined and they are trying to build it on various objects. In this article I will try to understand what a qubit built on an atom is. There is an article on the Internet “The qubit lasted 39 minutes at room temperature” . Such a qubit was created at Simon Fraser University (Canada). One of the developers of this qubit is Stephanie Simmons of the University of Oxford. He told us about this miracle.

As the article says:

“qubits were made from phosphorus atoms embedded in a very pure silicon crystal (pictured), by bombarding them with magnetic pulses to induce quantum superposition” .

Here are the photos of the lucky ones.
And here is a diagram of the setup where these phosphorus atoms were superimposed.

Installation seems complicated, but this is only at first glance. Let's take a closer look at her.

Measuring devices are marked in red. Wavemeter measures some parameters of radiation waves. Gaussmeter and Magnet control measures and controls magnetic flux. If their signals are not used for feedback, then they do not participate in the installation.

The blue color indicates the device that provides the corresponding magnetic flux through the qubit. It moves this magnetic field relative to the qubit along the arrow B1 , changes its strength. This is a complex device, but it is not essential for our business.

A detecting (reading) device is indicated in green. A 114 kHz signal is fed to the qubit, which passes through the qubit and strobes itself through a 1 microfarad capacitor. If the state changes in the qubit, then the read signal will somehow change.

The rest, uncolored part of the diagram, is devoted to the formation of such a pulse or several pulses as a result, which, after focusing on an atom or atoms of phosphorus, could transfer these atoms into a superposition, otherwise into a different state.

The developers claim that such a long-awaited and encouraging signal appeared and lasted 39 minutes, only while at a low temperature, and then disappeared. But the optimism of the developers is inexhaustible - they argue that this is possible at room temperature. This is a technical problem. It is worth a little tweak, add, rebuild and everything will learn. And you can believe in it 100%.

But what is this superposition signal?

In the last century, in the 60-70s, in the Soviet Union (possibly all over the world), watches with luminous hands were sold so that you could see the time in the dark. The arrows were covered with phosphorus, which glowed at night. But this light in the dark decreased and decreased, and if the clock is not kept in the light during daylight hours, then the next night the hands may not glow at all. That is, it required a kind of recharging. It is clear that during this recharging, photons of the visible spectrum transferred phosphorus atoms into an unstable, but close to stable, excited state. In this state, the atom after a while spontaneously radiated photon visible spectrum, and we saw light. The closer the excited state was to the stationary one, the later the spontaneous emission occurred.

There are countless such spontaneous emissions. Look at the chemical vibrations Belousov-Zhabotinsky . The spectrum of spontaneous emissions there is quite decent and the time intervals of excited states of substances are quite large. And what is the spectrum of invisible, or not yet invisible, spontaneous emissions is difficult to even imagine.

And with the help of all sorts of tricks, these happy scientists managed to artificially generate radiation, or a spectrum of several radiation, such that they transferred the phosphorus atom into an excited state, which lasted 39 minutes. After that, the atom spontaneously gave birth, which made the research team happy. Maybe they even threw their caps.

But what does all this work have to do with the quantum world and, accordingly, with the quantum computer? Yes, no, because a quantum computer should be built on a quantum of energy .

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