We all know that Schrodinger’s cat can be both dead and alive at once, but did you know that it can also be in two places at once?
Luckily for the cat, it’s just a metaphor, used to illustrate the Copenhagen interpretation of quantum mechanics. It says that microscopic matter can be considered to be in two quantum states at once before it is observed. The story says that the cat is sealed in a box along with a radioactive particle and a vial of poison gas. Radioactive particles decay randomly, so we have no way of knowing when the decay will happen. If the particle does decay, it triggers a mechanism to break the vial and the cat is killed. However, until the box is opened, we don’t know if the cat is alive or dead, so we say that it is both at once.
Scientists at Yale have now shown that the “cat” can be split in two, if the cat can be considered as electromagnetic waves trapped in two microwave chambers (aluminium boxes) connected by a superconducting channel. The channel, which is made of a sapphire chip and an aluminium circuit, acts as a switch which can be either on or off. Before the boxes are connected, the electric fields of the waves can oscillate in two different directions, and because we don’t know which it is before measuring it, we say that it is vibrating both ways. This is similar to saying that a guitar string is oscillating in two different directions simultaneously. The two possible vibrational directions are called “cat states”. Another way of thinking about the states is by considering how the photons which make up the microwave move – they are bouncing around inside the box randomly. When the boxes are connected, the electrical signals can travel to the second box, and since in quantum mechanics the link can be on and off, the cat is alive and dead in both boxes.
The team of scientists measured whether the boxes were still interacting when the connection was severed. To do this, they had to make a measurement which wouldn’t disturb the system from the state that it was in, which they did by counting the number of photons in each box. The numbers in each box were sometimes odd and sometimes even, but the total was always even, as the scientists expected. This means that the cavities work together whether or not the link between them is off!
This discovery, which scientists are calling “two-mode cat states”, could help us to measure the phase of light, or could even mean a breakthrough in quantum computing. Quantum computing has much higher processing speeds than normal computing and this development could mean faster processing speeds than we could ever imagine. In a normal computer, calculations are done in sequence but in a quantum computer multiple tasks can be done at once, because quantum bits, or qubits, are used. They can be in the “on” state and the “off” state at the same time, rather than having to choose between them. This two mode state is especially useful in optimisation problems, as all of the possibilities can be calculated simultaneously and the best one selected at the end. Doing this on a normal computer would mean calculating each possible scenario one by one, which could take years. If two qubits are linked, so that an action on one affects the other, they could perform tasks as a single unit, making quantum computing even faster.
Quantum computers have their downfalls though. They must be kept at very low temperatures, close to absolute zero. Errors are also caused by interactions with the external environment, which affects the qubits’ quantum properties. That’s where the cat comes in – if the qubits are linked it might be possible to correct the errors without disturbing the information. What seems like a small step in the world of the metaphor may in fact revolutionise quantum computing.