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MIT Technology Review

  • Yasunobu Nakamura


    WHILE EXPERIMENTING with ultrasmall superconducting transistors at NEC in Tsukuba, Japan, Yasunobu Nakamura became familiar with quantum computing and had a vision. Each of his transistors featured an island of aluminum just 20 nanometers thick—so small that its state could be altered with a single electron. This exquisite sensitivity was exactly what was needed to create a quantum bit, or qubit, the fundamental element of quantum computing, which promises some day to speed computation exponentially. One of quantum computing’s basic requirements—which had been contemplated for two decades—was controlled operation of a qubit, and Nakamura achieved it in 1999.By applying voltage pulses of varying lengths, he dictated whether the island had an extra pair of electrons (the 1state),no extra electrons (the 0 state),or a combination of the two—a quantum-mechanical state that enables qubits to store far more information than conventional bits. Next, Nakamura and a collaborator got two qubits to interact in a manner that had been predicted but never demonstrated. The challenge ahead is to control coupled qubits long enough— microseconds— to perform meaningful computations. Meanwhile, Nakamura says, people should start preparing some good applications for quantum computers.