# Success in controlling multi-photon transitions of a superconducting flux qubit

## －One step closer to realizing a quantum computer－

NTT Basic Research Laboratories in collaboration with Japan Science and Technology Agency (JST-CREST) have succeeded in flipping supercurrent flow (Fig. 1) (quantum state transition) in each case of one-, two-, and three-photon absorption process by irradiating resonant microwave photons (Fig.2) to the superconducting flux qubit. From Ramsey interference experiment, we have also observed characteristic oscillating pattern (Fig. 3) therefore, we have succeeded in coherent control of a qubit which is essential if quantum computation is to work. We have confirmed that quantum mechanics, which is usually applied to microscopic objects such as elementary particles and atoms, can also be applied to the macroscopic state(consisting of millions of Cooper pairs) in a superconducting flux qubit of six micrometers in size. From these experiments, this device has proved to be a promising candidate as a quantum computer building block.

=> Press Release

=> Superconducting Quantum Physics Research Group

[Reference: S. Saito et al., Phys. Rev. Lett. 93, 037001 (2004). ]