Quantum computation is the current high visibility fad in atomic physics. These computers operate along the same lines as normal computers but every quantum bit (qubit) is both a one and zero at the same time. Only when the final result is desired do we measure the qubit state and receive either a one or a zero. The mathematical operations performed by a quantum computer alter the probability of receiving a one or a zero. The advantage is that quantum computers can potentially perform certain types of calculations much faster than classical computers (database searches and factoring large numbers are examples). The problem is that quantum computers rely on creating and controlling entangled quantum states, which are highly delicate beasts. The traditional approach to this has been to carefully control the interactions between qubits on a pair-wise basis (e.g., only two qubits can interact at a time). Every time you switch the interaction between two qubits on or off you run the risk of destroying that which you are trying to control, thus you can't do many computations in a row. Not only that but you have lost much of the parallelism for which you are doing a quantum computation in the first place.

Now a new approach to the problem is under development. The operations between qubits are still carefully controlled (otherwise no computation would be possible) but the interactions between qubits are not switched on and off, instead they are always on. By developing a method by which quantum calculations can be performed even when an operation on one qubit effects all the remaining qubits has numerous advantages. The biggest fundamental advantage is that the implementation of many common algorithms can be simplified. More practically, this method allows experimental physicists to start using coupled systems such as quantum dots, which have a much better chance of leading to practical computers that can actually scale to the point where they are useful.

One of the distinguishing concepts is that any successful implementation of this algorithm is automatically a programmable multi-bit core much like the processing units of early microprocessors. The big question is can we build it? Well that is a definite maybe, building quantum dots that are coupled together is now a fairly common lab practice. The problem is that these dots are also coupled to the rest of the substrate so the carefully constructed quantum states are easily destroyed by the very material they are built upon. I guess Hannibal can wait a week or two before digging into the new quantum processor core architectures.

## No Comments