This opens the way for quantum memories

Jan 20, 2010 11:43 GMT  ·  By
Qubits are made up of controlled particles and the means of control (as in the devices that trap particles and switch them from one state to another)
   Qubits are made up of controlled particles and the means of control (as in the devices that trap particles and switch them from one state to another)

One of the most promising goals in science today is the creation of a quantum computer, a device that will be several orders of magnitude faster and better than any existing supercomputer. However, the challenges ahead are up to the rewards, and physicists around the world are still struggling with the basics. For instance, they are now trying to obtain a stable type of quantum memory that is able to store data effectively, and to produce a strong signal. This has proven elusive, but now researchers at the University of Stuttgart, in Germany, believe they may have managed a breakthrough in the field.

Previous research has demonstrated that one of the best approaches to constructing quantum bits (qubits), the basic units of a quantum system, is to embed nitrogen atoms inside diamonds. This approach has proven successful to some extent, but research teams have discovered that the signal generated by these qubits is still fairly weak, and have begun to look for ways of boosting it. What the German team did was basically demonstrate a new, roundabout way of making this particular type of qubits emit signals much stronger than ever before.

Details of its achievements appear in the latest issue of the scientific journal Physical Review B, and are also reviewed in a “Viewpoint” published in the January 19 edition of the esteemed publication Physics. The team also highlights the fact that qubits reset themselves after each reading, which contributes to the overall difficulty of the task at hand. The data a qubit holds can be encrypted, for example, in its spin, or some other physical property. As part of a quantum system, every time an outside observer sees the actual state of the qubit, the unit loses all of its information. In practical terms, this translates into a single opportunity to measure the data, with no leeway for errors.

The Stuttgart team managed to modify the nitrogen qubits in such a manner that the units changed their states twice before the information was lost, rather than once. The number of processes that occur in the nitrogen atom before the data it encodes is finally destroyed therefore triples, which contributes directly to increasing the intensity of the previously weak signal. For all practical applications, the signal is still weak despite these improvements, but the work brings a ray of hope that other clever innovations could lead over the years to the development of methods that allow for qubits to be written and read at room temperature – a basic condition for practical quantum computers.