The well-known cat-in-a-box theoretical experiment proposed by Austrian physicist Erwin Schrödinger is an instance of one of the basic properties of quantum mechanics, namely the unpredictable mechanism of particles at the quantum level.
This makes working with quantum mechanics extremely challenging, but now, a team of physicists believes that quantum predictions can actually be made. In a research carried out last year and published in the journal Nature, the team demonstrated their capacity to predict something known as quantum jump, and even reverse the process after it has begun.
They have been able to, therefore, ‘save’ Schrödinger’s cat.
Saving Schrödinger’s Cat
For those not familiar with Schrödinger’s cat experiment, here’s a quick commentary. The physicist imagined the following scenario: there’s a cat in a closed box. In the same box, there’s also a source of radioactive decay, a Geiger counter, and a sealed flask of poison.
If the Geiger counter perceives the radioactive decay of a single atom, it breaks the flask of poison, which kills the cat. There is no way to look inside, so you have no way of telling whether the cat is alive or dead. It exists in a state of both until you open the box.
The moment you do so, it is either one state or the other, and cannot be both at the same time anymore. This imaginary experiment is a metaphor for what is called quantum superposition, in which a particle can exist in multiple energy states simultaneously until the point at which you observe it. Once observed, its abrupt and random transition between states is known as a quantum jump. It is this jump that physicists have been able to not only predict but also manipulate, intentionally changing the outcome.
The researchers, led by a team of physicists at Yale University, managed to do so employing artificial atoms known as qubits, which are also used as the usual units of information in a quantum computer. Each time you measure a qubit, it carries out a quantum jump. They are rather unpredictable in the long term, which can lead to issues in quantum computing.
“We wanted to know if it would be possible to get an advance warning signal that a jump is about to occur imminently,” said physicist Zlatko Minev of Yale University.
The Sliding of a Lever
The team created an experiment to evasively observe a superconducting qubit, using three microwave generators to irradiate the qubit in a closed 3D chamber made of aluminum. The radiation shifts the qubit between states, while another beam of microwave radiation observes the box.
When the qubit is in an energetically ground state, the microwave generates photons. An abrupt lack of photons means that the qubit is at the edge of making a quantum jump into an excited state. The study demonstrated that it wasn’t so much a jump as a transition, similar to a slide of a lever.
Therefore, another accurately timed beam of radiation can reverse the quantum jump after it has been spotted, switching the qubit back to its original ground state; or, to refer to the Schrödinger’s cat’s metaphor, prevent the cat from dying and bring it back to life, or the ground state.
There’s still a long-run unpredictability as the experts cannot, for instance, foresee exactly when a quantum jump is going to take place; it could occur in five minutes or five hours. However, once it has started, it always follows the same trajectory. Throughout 6.8 million jumps the team witnessed, the pattern was constant.
“Quantum jumps of an atom are somewhat analogous to the eruption of a volcano,” Minev said. “They are completely unpredictable in the long term. Nonetheless, with the correct monitoring, we can, with certainty, detect an advance warning of an imminent disaster and act on it before it has occurred.”
The paper detailing the experiment and findings has been published in Nature.