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Research group demos the first controllably coupled qubits

Posted: 09 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:quantum bit circuit? qubit circuit? controllably coupled qubits? quantum computing?

NEC Corp., Japan Science and Technology Agency (JST) and the Institute of Physical and Chemical Research (RIKEN) have demonstrated the world's first quantum bit (qubit) circuit that can control the coupling strength between qubits.

The technology resulting from the three companies' joint research, Quantum Coherent Tunable Coupling of Superconducting Qubits, is claimed to be vital for the realization of a practical quantum computer.

Towards quantum computing
A quantum computer is touted to outperform even today's most modern supercomputers. Its actual computing is achieved by manipulating the quantum state of qubits in time sequence by external controls. To achieve this, it is necessary to control the states of individual qubits, the states of two qubits (logic operation) and the coupling between qubits.

Recognizing these considerations, NEC, JST and RIKEN partnered to develop key technologies for the first solid-state qubit and the first two-qubit logic gate, based on solid-state technology that can integrate qubits. Then, the group addressed the controllable coupling of qubits as the next logical step in realizing a practical quantum computer. The research result represents the world's first successful demonstration of controllably coupled qubits, said the group.

Coupling of qubits has been difficult to control. To achieve this control, the research group devised a mechanism that employs another qubit in between the two qubits for coupling. The coupling qubit functions as a non-linear transformer that can turn on and off the magnetic coupling between the two qubits. Then, the on/off control is achieved by simply inputting a microwave. Notably, the coupling operation was achieved without shortening the lifetime of each qubit. Scalability is also realized through the repetition of coupled two-qubit unitsa feature necessary for future quantum computers.

To demonstrate the feasibility of the controllable coupling scheme, the research group employed a coupled two-qubit system (the smallest quantum logic unit), to implement a multi-quantum control experiment, in which coupling is turned on and off. Based on this, a simple quantum protocol was successfully demonstrated, which allowed controllable coupling for the execution of quantum algorithms.

A part of the joint research has been carried out under the JST project, Core Research for Evolutional Science and Technology (CREST), which focuses on the creation of new technology for the realization of quantum information processing.

NEC, JST and RIKEN plan to implement a larger-scale, more elaborate quantum computation in the near future.

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