Physicists at the University of California, Berkeley, have managed to peek inside the box housing Schrödinger’s Cat. By gently probing a qubit created via a small superconducting circuit, they were able to gain information about the qubit’s state without forcing a collapse from its superposition. This would allow for better exploitation of quantum mechanic’s bizarre superposition principle, where a quantum particle exists in multiple states simultaneously.
Superposition is best described by Erwin Schrödinger’s infamous Schrödinger’s Cat thought experiment, where a cat is placed in a box with a vial of poison controlled by the random decay of an atom; if the atom decays, the poison is released, killing the cat. Any measurement of the system will affect the decay of the atom, since the atom’s decay will only take a definite value upon measurement, so an outside observer cannot determine if the cat is still living. As a result, the observer must consider the cat to be in a superposition of both dead and alive.
This property of quantum particles existing in a superposition of multiple states is utilized by modern applications of quantum mechanics, such as quantum computing. Unlike classical computing, in which a bit has a discrete value of 0 or 1, a qubit assumes a superposition of 0 and 1; only upon a final measurement does the qubit collapse to a specific value. This aspect of qubits has been a roadblock for researchers, as qubits need to hold the superposition long enough to perform quantum algorithms and calculations.
By making gentle, indirect measurements and introducing feedback to counter any shift from superposition, the team at UC Berkeley was able to prevent the qubit’s collapse. The team, led by Dr. R. Vijay, used a small superconducting circuit as a qubit, and created a superposition by oscillating its state between values of 0 and 1. By measuring the frequency of the oscillations, and not the direct value of the qubit, the physicists were able to gain information about the system, while keeping the qubit in superposition for the duration of the experiment.
This small peek at the quantum system is akin to putting on blurry glasses and taking a quick look inside the box containing Schrödinger’s cat. While the observer may not be able to tell if the cat is alive or dead, they may be able to obtain some information about the system, without having an adverse effect on the superposition of the decaying atom.
While the measurement was not strong enough to force a full collapse from superposition, there was a random change in the oscillation rate. However, by taking a quick measurement and inducing feedback to return the oscillations to the original value, the team prevented the qubit from settling into any definite state.
The team is not the first to attempt stabilizing the qubit through induced feedback, but a new kind of amplifier produces a signal small enough to prevent noise and contamination being introduced to the system, while producing a signal large enough to detect and correct. By using such amplifiers, researchers are coming closer to implementing quantum error controls, which could be used to extend superposition of a qubit in quantum computing.
Leave a Reply