A quantum computer operates on the principles of quantum mechanics, a unique set of rules that governs at the extremely small scale of atoms and subatomic particles. When dealing with particles at these scales, many of the rules that govern classical physics no longer apply and quantum effects emerge. A quantum computer is able to perform complex calculations, factor extremely large numbers, and simulate the behaviors of atoms and particles at levels that classical computers cannot.
Quantum computers have the potential to provide more insight into principles of physics and chemistry by simulating the behavior of matter at unusual conditions at the molecular level. These simulations could be useful in developing new energy sources and studying the conditions of planets and galaxies or comparing compounds that could lead to new drug therapies.
A regular computer consists of billions of transistors, called bits. Quantum computers, on the other hand, are based on quantum bits (qubits) that can be made from a single electron. Unlike ordinary transistors, which can be either “0” or “1,” qubits can be both “0” and “1” at the same time. The ability for individual qubits to occupy these superpositions simultaneously in multiple states underlies the potential of quantum computers. Just like ordinary computers, however, quantum computers need a way to transfer information between qubits, and this presents a major challenge.
If certain kinds of particles have the same magnetic moment, they cannot be in the same place at the same time; that is, two electrons in the same quantum state cannot sit on top of each other. If two electrons are in opposite states, they can sit on top of each other. If one electron is up and another is down and they are pushed together for just the right amount of time, they will swap.
A method of transferring information and correcting errors within a quantum system was developed that relays information by transferring the state of electrons. To force this phenomenon, researchers cooled down a semiconductor chip to extremely low temperatures. Using quantum dots — nanoscale semiconductors — they trapped four electrons in a row, then moved the electrons so they came in contact and their states switched.
This work demonstrates that information in quantum states can be transferred without actually transferring the individual electron spins down the chain — a step towards showing how information can be transmitted quantum-mechanically.