NEC, Japan Science and Technology Agency (JST) and the Institute of Physical and Chemical Research (RIKEN) have now presented the first qubit circuit (quantum bit; qubit) which can manage the power of connected qubits. Such a circuit has been longed for by researchers worldwide for some time now and it’s a big step toward building a real quantum computer. The possibilities to use more than one qubit have been rather limited in the past, especially if you want good control of them. D-Wave presented its quantum computers a while back, which it claims to be the first working quantum computer, but the company and its demonstrations have been questioned more than plenty. This breakthrough is nothing but crystal clear, that is if you can call quantum equations crystal clear.
Quantum computers are expected to become the next generation of supercomputers sporting performance we could only dream of before. BlueGene/L will be put to shame by a relatively small quantum computer. By manipulating the quantum state of the qubits in time sequence they can make them work together. To be able to manipulate the quantum state of the qubits you have to be able to control each qubit, control them in pair for logical functions and at the same time control the gates between them.
The three have previously presented a ”solid-state” qubit and the first logical gate between two qubits. When doing so they also announced that the next step would be to build a circuit for controlling the qubits (a bit cocky) and so they have. During the demonstration they presented two connected qubits and how the circuit managed to manipulate these and make them work together.
The connection between the qubits is a non-linear transformer that can turn on or off the magnetic connection between the qubits through a small microwave. This isn’t that far from how D-wave says that their gates work. This circuit also makes it possible to repeat pair of qubits in a theoretical infinity, a must for future quantum computers, and something that D-wave as claims possible (although it has also revealed that the practical limits is somewhere around 1,024 qubits for them).
NEC and its companions have released some more information that can be found in Science Vol. 316. no. 5825, 723 – 726; Quantum Coherent Tunable Coupling of Superconducting Qubits or online here.
