Schrödinger’s cat may seem like an arcane thought experiment. But it could have real-world consequences for quantum computing.
Quantum mechanics states that subatomic particles can exist in a superposition of quantum states—or two simultaneous modes of being. But direct observation causes those various possibilities to collapse into one physical reality. Erwin Schrödinger put this idea into a macroscopic context, by analogy: he said that if a cat is sitting inside a box, and a vial of poison is released into the box, the cat will be both dead and alive until you open the box and observe the reality. The cat is either alive or dead.
Here’s Josh Sokol, reporting for New Scientist:
Microwave photons trapped in a box can be coaxed into a so-called “cat” state. Normally, electromagnetic waves in the box will oscillate in strength, like a pendulum sweeping back and forth. But it’s possible to introduce the opposite wave into the box, creating a cat state that is doing two seemingly contradictory things at once.
“A mechanical analog of this would be a pendulum that is simultaneously oscillating to the left and to the right,” says
Chen Wang , then at Yale University.
Wang’s team did something similar using two boxes (or “cavities”) of aluminum. They connected these two cavities using a superconducting sapphire chip and aluminum circuit as a channel though which electric signals could travel. The state of the channel (open or closed) determines the frequency of the oscillations inside the cavities. But in a quantum world, the channel can be open and closed at the same time—making the photons inside the cavities oscillate at two different frequencies at once.
The team then effectively sawed the box in half; in other words, they severed the link that was the channel to see if the photons inside the individual cavities were still “working together,” meaning they still added up to a true state of quantum superpositions, even when its components were broken down into smaller parts. The answer? They did add up to the expected quantum state—the cavities had been entangled.
These entangled cavities, it turns out, could help scientists measure phases of light more accurately. They could also function as qubits, or quantum bits of information. In classical computing, a bit represents either a zero or a one. In quantum computing, on other other hand, qubits represent either a zero, a one, or a superposition of both. Linking qubits in this way could improve the efficiency and power of quantum computers.
