Building a quantum computer. Josephson junction qubitд

At present, only the lazy is not talking about a qubit with full consciousness of the matter. But, probably, one storyteller would be enough, since everyone says the same thing.

You can say: there is one truth, therefore there is only one story. Then the statement that one in 10 thousand understands quantum mechanics is not true. Every second person understands it. And for a popularizer, it’s twice two. But let's essentially.

This is what Wikipedia writes about it:

A qubit (q-bit, cube, qubit; from quantum bit) is a quantum discharge or the smallest element for storing information in a quantum computer .

I found on Wikipedia the article "Physicist Alexei Ustinov on Russian qubits and the prospects for their use", the data for which is taken from "Lenta.ru". Here Ustinov believes that “qubits, they seem to be realized in the form of completely different objects - atoms, ions, photons, atomic spins, and so on”. Under his leadership, the qubit was implemented at the Josephson junction. This is what it looks like:

It turns out that a qubit (aluminum strip) is an information keeper, and information carriers are currents that flow in this frame in opposite directions. Approximately as I depicted in the picture.

If the internal resistances of the current sources are much greater than the resistance of the conductor, then the currents from each source in it will flow in opposite directions and in any proportions.

In a qubit, currents are excited by magnetic fields. If the current flowing, say clockwise, is taken as one, then the current flowing in the opposite direction will be considered zero. Currents can be of different magnitudes and, what is important, simultaneously. There can be endless such different states. Each such state can be measured as a phase shift of some signal passing through this qubit. The magnitude of the phase shift depends on the magnitude of the current in the qubit, more precisely, on the magnitude of the perturbation of this current, in fact, the sum of currents in opposite directions. The number of phase values from zero degrees to 360 degrees is also infinite. Therefore, each state of a qubit can be assigned a specific phase state.

The scheme seems to be simple, but there are many problems. One of them is to achieve long-term storage of the qubit in the desired state. External influences, especially magnetic ones, tend to destroy the state of the qubit. Although the excited current in a superconductor can flow for a long time, in this case it is microseconds, in the extreme case, milliseconds. What we have time to do with the qubit during this time thet is good.

The problem is how to distinguish these phases from each other. Well, there it is easy to distinguish a zero phase from a phase of 180 degrees, 90 degrees, or even 45 or 30 degrees. Why not shift these phases, even with a magnetic field, even with a ferromagnet, as Valery Ryazanov from Chernogolovka suggests, but the question is how to distinguish zero degrees from 5 or 11 degrees? will not be removed from the agenda. And the determination of the phase must be done in each cycle of reading and writing. It seems to me that in this case it is easier to work with a normal bit. It is represented by a certain number of electrons in the container. And when this capacity is filled with electrons, their number changes in the same way as the current in a qubit. The only difference is that the number of electrons, although large, is not infinite. And they are perhaps easier to count than to accurately measure the phase. The phase of 1 degree is unlikely to be measured, but 360 electrons are easier to count.

Well, that's not the point. Even though currents transformed into degrees, encode information in a qubit, even though the number of electrons in a bit will still be only the basis of calculus. If you encode (write and read) information with zero and one, that's the binary base. When encoded by zero, one, and minus one, this is a ternary base. Several computers were made in the USSR on this basis. With this base, 9 numbers can be encoded with two digits, in contrast to 4 numbers encoded with two binary digits. And with three digits, the number of encoded numbers from 8 (binary system) increases to 27 (ternary system). And so on.

Of course, you can sing an endless song about how everything is not so in the quantum world, but how unknown. Everything there is in an inexplicable superposition and the like. But at the output you get a specific tangible signal, although not accurate, erroneous, probabilistic, which then has to be corrected, but completely cleared of any superposition. At this time, this signal is the only one. And no parallelism is observed here. Now, if you separated the currents representing zero and one, and determined their phases at the same time, then it would be a parallel reading. Moreover, even if these currents do not correlate at all. One could write down one task on the clockwise current, and the other on the opposite current. But this is practically the same as two digits in a regular computer.

These experiments with such a qubit were carried out by Professor Alexei Ustinov.

“Are there enough laboratories in the world doing them now? about a dozen collectives can measure the properties of qubits, including mine in Karlsruhe, Germany ”.

And although it started more than 7 years ago, no results are visible . The qubit did not work on Josephson junctions. It has nothing to do with the quantum world.

A quantum computer should be built on a quantum of energy , which eminent scientists do not even suspect.

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