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May 03, 2007

NEC, JST and RIKEN successfully demonstrate world's first controllably coupled qubits

More competition for scalable quantum computer solutions.

UPDATE: Dwave scientific paper that they achieved this goal first
Dwave's Geordie Rose indicates that the 16 qubit demo machine had 42 such couplers.

NEC Corporation, Japan Science and Technology Agency (JST) and the Institute of Physical and Chemical Research (RIKEN) have together successfully demonstrated the world's first quantum bit (qubit) circuit that can control the strength of coupling between qubits. Technology achieving control of the coupling strength between qubits is vital to the realization of a practical quantum computer, and has been long awaited in the scientific field.


NEC, JST, and RIKEN have already announced successful development of key technologies for the world's first solid-state qubit and the world's first two-qubit logic gate, based on solid-state technology that excels in its ability to integrate qubits. Following these achievements, the research group addressed the controllable coupling of qubits as the next logical step in realization of a practical quantum computer. Their new research result represents the world's first successful demonstration of controllably coupled qubits.

To date, the coupling of qubits has been difficult to control. In order to realize this control, the research group devised an original mechanism that employs another qubit in between the two qubits for coupling. The coupling qubit functions as a non-linear transformer that is able to turn on and off the magnetic coupling between the two qubits, and on/off control is achieved simply by inputting a microwave. Moreover, coupling operation has been achieved without shortening the lifetime of each qubit. Scalability is also realized through the repetition of coupled two-qubit units - a feature necessary for future quantum computers.

To demonstrate the operation feasibility of the controllable coupling scheme, the research group employed a coupled two-qubit system, the smallest quantum logic unit, to carry out a multi-quantum control experiment involving the turning on and off of the coupling. As a result, a simple quantum protocol has been successfully demonstrated, allowing controllable coupling for the execution of quantum algorithms.

In the near future, NEC, JST, and RIKEN, plan to implement a larger-scale, more elaborate quantum computation, aiming for the realization of a practical quantum computer.

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