The volatility of qubits (or quantum bits) is one of the biggest challenges in quantum computing. But figuring out a way to catch an artificial atom (containing a qubit) in mid quantum jump – and meddling with the outcome just blows open the delirious confinement invoked by the quantum physics famous Schrödinger’s cat experiment.
What is Schrödinger’s Cat?
Schrödinger’s cat is a thought experiment by Austrian physicist Erwin Schrödinger. It is used to illustrate the concept of superposition – the ability of a particle/system to exist in more than one state at the same time – and the weirdness of particle at quantum level, the hallmark of quantum mechanics.
The experiment involved penning up a cat in a sealed along with a tiny bit of radioactive substance, a Geiger counter and a poison, which in the course of an hour, will be triggered if an atom of the radioactive substance decays. So basically, the cat is left in a box with 50% chance of being killed in the next hour. But on the basis of quantum physics, as Schrödinger emphasized, the instant someone opens the box, the cat is either dead or alive, at the same time.
We can only see a single definite state when someone opens the box. Until then, the cat is a smudge of probability – half dead and half alive.
An atom can have two possible energy levels – the ground state, which describes the lowest energy state that an atom can have and the excited state, which describes a higher energy state after an atom absorbs energy.
If you have to shine some laser in it, you’re the giving something to give the atom some energy so it goes from its original state, the ground state to excited state instantaneously. That’s the notion of quantum jump. Later, a photon can come back out again and the atom switches back from the excited state to the ground state and that’s another quantum jump.
The important thing here is that the jump is discrete and the change in state is entirely random when observed. Or is it?
In a latest experiment performed at Yale University, a team of physicists pioneered the actual workings of a quantum jump, and revealed that the jumps long thought to be instantaneous, take time and they are not as random as prime movers of quantum physics previously thought.
Qubit or quantum bit is the fundamental unit of quantum information. Unlike a computer bit which can hold only either 0 or 1 at one time, a qubit can hold both 0 and 1 at the same time. This is known as the superposition state. To put it in layman’s term, in quantum computing world we have millions of options for outcomes at a time. But when the qubit switches from one state to whatever state it’s going to wind up being when observed (simply put, makes a quantum jump), it must be crucially dealt with. Because in developing quantum computers, the qubits are basically the manifestation of computational errors.
“These jumps occur every time we measure a qubit,” said Michel Devoret , the Professor of Applied Physics and Physics at Yale in a news release. “Quantum jumps are known to be unpredictable in the long run.”
“Despite that,” added Zlatko Minev , the lead author of the study, “We wanted to know if it would be possible to get an advance warning signal that a jump is about to occur imminently.”
Catching a Quantum Jump Mid-Flight
To predict and catch the jump, the team adopted a special approach to observe a superconducting artificial atom (containing a qubit). They also developed a system consisting of three microwave generators to irradiate the atom sealed shut in a 3D cavity made of aluminium.
As microwave radiation budges the artificial atom, it pushes the qubit between energy states. So basically, fueling the quantum jumps. The quantum signals of these jumps are continuously being monitored in real-time by firing another beam of microwave radiation. So when the qubit is in ground state, the beam emits photons. And a sudden absence of photons means the qubit is about to make another jump.
In essence, the whole experimental set-up is kind of an early-warning system for quantum jumps.
“The beautiful effect displayed by this experiment is the increase of coherence during the jump, despite its observation,” explained Devoret.
“You can leverage this to not only catch the jump, but also reverse it,” Minev then added.
Saving the Schrödinger’s Cat
Now, let’s slide back to the Schrodinger’s cat metaphor. As researchers pointed out while the jumps appear non-continous and random over the long haul, if they can crank up their experiment to reverse the jumps means the evolution of each completed jump is of continuous, coherent and deterministic nature. So apparently, sending or reversing the qubit back to its ground state means saving the Schrodinger’s cat from the proverbial doom and bringing it back to life.
“Quantum jumps of an atom are somewhat analogous to the eruption of a volcano,” explained Minev. “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.”
So from this groundbreaking experiment, the physicists have essentially figured out a way to solve quantum computing’s error problem. The discovery is a monumental push towards understanding and controlling quantum information. This could potentially pave the way for the development of quantum computers that can reliably manage quantum data, detect and correct errors as they happen.
The study has been published in the journal Nature, and it’s titled “To catch and reverse a quantum jump mid-flight.”