Quantum breakthrough: Scientists generate qubits within semiconductors
March 26, 2012
A significant step on the path to quantum computing has been taken by an international team of researchers applying a 22-year old theory. They have succeeded in creating quantum bits within a semiconductor for the very first time.
Classical bits can be assigned one of only two values which are typically used to reflect on or off, true or false, yes or no, and other binary states. In each of these cases, the first, positive state is typically represented by a 1, and the second a 0 (the word bit is itself a contraction of binary digit - binary numbers consisting of strings of 1s and 0s). In current electronics devices, the 1s and 0s are conveyed by voltage variations.
Like a classical bit, quantum bits (or qubits) take on values of 0 or 1, but unlike a classical bit, a qubit can assume both values simultaneously, and to varying degrees, through what is known as superposition. Superposition allows a qubit to be assigned the value of a complex variable, and this promises to one day significantly increase the computational power of computers - especially when tackling certain types of problems in fields including encryption and quantum research.
But qubits are fickle things, having a tendency to lose superposition under observation (recall Schrödinger and his unfortunate cat). Until this latest breakthrough, qubits had only been successfully created in large vacuum chambers. But by using a theory proposed 22 years ago by physicist Prof. Dr. Andreas Wieck of the Ruhr University Bochum (RUB), researchers have used a dual-channel system to create qubits in a semiconductor.
Electrons are passed through a semiconductor until they arrive at a fork. At the fork, each electron takes both paths simultaneously. When the two paths are merged, the two electron waves interfere with each other, and, some of the time, qubits with more than one state occur, caused by the overlap of the waves. At this stage, only a few percent of electrons emerge as qubits, but the RUB researchers hope to improve on the success rate by employing semiconductor crystals with greater electron densities - the current round of research used gallium arsenide.
The research, titled Electrical control of a solid-state flying qubit, was published in Nature Nanotechnology last week.