Physicists have found a way to save the Schrödinger cat

The famous thought experiment of the Austrian physicist Erwin Schrödinger “cat in a box” is an illustration of one of the defining characteristics of quantum mechanics - the unpredictable behavior of particles at the quantum level.

This unpredictability makes working with quantum systems incredibly difficult. But what if we learned to make "quantum predictions"? A team of physicists believes that this is possible. In a new study, they demonstrated their ability to predict something called the quantum leap, and even the ability to completely change the process after it began.

In fact, according to their own assurances, they “saved” the Schrödinger cat

Let's start by refreshing the memory of who this very cat is. Erwin Schrödinger came up with a scenario: there is a certain closed box in which the cat is located. In addition, the box contains a radioactive element, a Geiger counter and a sealed flask with poison. The element is so small that only one atom can decay in an hour, but with exactly the same probability this may not happen. If the Geiger counter detects the decay of this isotope atom, it will break the flask with poison and the cat will die.

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There is no way for the observer to look inside, and therefore it is impossible to know for sure whether the cat is alive or dead. Until the moment you open the box and see it, it exists in both of these states. At the very moment when the box is opened, one of the two options will be chosen by chance and the cat’s ability to be both alive and dead will disappear.

Of course, all this is just a funny metaphor for a phenomenon that physicists call a quantum superposition, in which a particle (atom, electron or photon) can exist in several energy states at the same time - right up to the point where an observer appears. As soon as this happens, there will be a sudden transition between energy states, known as a quantum leap.

Previously, scientists could only observe this phenomenon, but now physicists have learned not only to predict, but even to manipulate circumstances so as to consciously change the result of the jump in the direction they need. To this end, researchers led by a group from Yale University used artificial atoms called qubits, which are also used as the basic units of information in a quantum computer. Each time you measure a qubit, it performs a quantum leap. In the long run, such leaps are unpredictable, and therefore attempts to build quantum computing were very problematic.

Therefore, the team developed an experiment for indirect observation of a superconducting qubit, using three microwave generators to irradiate the qubit in an airtight three-dimensional aluminum casing. This microwave radiation switches the qubit between energy states, while another microwave beam controls the box. When the qubit is in the ground state, the microwave beam produces photons. The sudden absence of photons means that the qubit is about to make a quantum leap to the excited state.

The study showed that it was not so much a leap as a transition; not a flick of a switch, but possibly a sliding lever. Consequently, another precisely synchronized radiation pulse can reverse the quantum jump after it has been detected, sending the qubit back to its ground state; or, based on the metaphor of the Schrodinger cat, do not let the cat die and bring her back to life.

In the long run, unpredictability still takes place. For example, researchers still cannot accurately predict when it will happen - it can be either five minutes or five hours. But once the jump has begun, it always follows the same path. The team proved this by comparing 6.8 million jumps - they were all consistent. “The quantum jumps of an atom are somewhat similar to volcanic eruptions. They are completely unpredictable in the long run. However, with proper observation, we can confidently detect an early warning of an impending disaster and react before it occurs, ”the scientists explain.

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