Pacemaker for Schrödinger cat

    Scientists from the University of California at Berkeley managed to conduct an experiment that allows us to say whether the notorious cat is alive or not.

    Let us briefly recall what kind of exotic animal it is and how it relates to IT. Erwin Schrödinger set up the following thought experiment:
    A cat is locked in a steel chamber along with the next infernal machine (which must be protected from direct cat interference): inside the Geiger counter there is a tiny amount of radioactive substance, so small that only one atom can decay within an hour, but with the same probability and do not fall apart; if this happens, the reading tube discharges and a relay activates, lowering the hammer, which breaks the cone with hydrocyanic acid. If we leave this whole system to ourselves for an hour, then we can say that the cat will be alive after this time, as long as the atom does not decay. The very first decay of an atom would poison a cat. The psi function of the system as a whole will express this, mixing in itself or spreading the living and dead cat (sorry for the expression) in equal proportions.

    Typical in such cases is that the uncertainty initially limited by the atomic world is transformed into macroscopic uncertainty, which can be eliminated by direct observation. This prevents us from naively accepting the “blur model” as reflective reality. This in itself does not mean anything obscure or controversial. There is a difference between a fuzzy or defocused photo and a picture of clouds or fog.

    Such "ambiguity", in theory, is the basis of quantum computing - thanks to it, calculations on quantum computers (QC) are performed using quantum bits (qubits), which simultaneously store 0 and 1, taking a certain value only "under the microscope", that is, when direct measurement. It is the latter feature that is the stumbling block for building QC, because any planned intervention will be regarded by the system as a measurement, which, in turn, will lead to errors in the calculations.

    R. Vijay, the head of the research group, claims that they were able to "open the box with the cat." The idea of ​​the experiment is to measure the state of zero or unity indirectly - as if we were opening the box and looking there with one eye, and even squinting very hard.

    Scientists created a small superconducting chain (which is usually used as a qubit in the prototypes of quantum computers) and launched, as it can be expressed, a superposition of states 0 and 1, as a result of which the qubit cyclically changed the set of states. After that, the frequency of these oscillations was measured, which allows you to indirectly indicate the state of the system at a certain point in time, without forcing it to choose whether it is in zero or in unit.

    Despite all the theoretical elegance of the experiment, which made it possible not to destroy the quantum superposition, everything turned out to be not so simple - during measurements the system spontaneously changed the oscillation frequency, which could not be predicted. Scientists were able to circumvent this problem due to the fact that the measurements were carried out quickly enough to introduce the opposite disturbance, equal in magnitude, but opposite in direction, returning the system to the oscillation frequency without external interference. In fact, this is the principle of operation of the pacemaker - when the heart rate deviates from the correct one, the device sends an impulse that corrects the operation of the "flame motor".

    The idea itself is not new, but previous researchers did not succeed: compensations that did not violate the superposition were too weak to register, and large ones made noise in the system.

    The results are not yet ideal, but they are - the qubit has existed in the required state for microseconds - this is an eternity for such experiments, and may be enough for use in calculations.
    According to the team leader, this is a big step for controlling errors in quantum computing. Well, wait and see.
    PS This is an adapted translation of this article , alas, I do not have enough karma either for a post in the "Translations" section or for "Popular Science", I chose the most related topic where I can post it.

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