Research Areas
We are studying macroscopic quantum coherence that occurs in small Josephson junction circuits. In the system, charge and phase degrees of freedoms co-exist, and their coherent control can be exploited as quantum bit (qubit), the basic component of the quantum computer. We have demonstrated such coherence in the superconducting system in 1999, and subsequently pioneered the superconducting solid state qubit technology. So far, we have demonstrated the operation of a 2-qubit-quantum logic gate, first time by a solid-state system. A highly efficient single-shot measurement was also demonstrated. The solid-state system is considered indispensable in realizing the integration required for a practical quantum computer. Recently, we have successfully demonstrated the execution of a small scale quantum protocol by developing a universal set of quantum logic gates with a qubit-coupling switch.
Research Subject
| (1) |
Quantum coherence in superconducting circuit |
| (2) |
Quantum bit |
| (3) |
Quantum information processing |
List of Selected Publications
| (1) |
Astafiev, O., Inomata, K., Niskanen, A.O., Yamamoto, T., Pashkin, Yu. A., Nakamura, Y., and Tsai, J. S.:
"Single artificial-atom lasing."
Nature, 449, 588 (2007) |
| (2) |
Niskanen, A. O., Harrabi, K., Yoshihara, F., Nakamura, Y., Lloyd, S. and Tsai, J. S.:
"Quantum Coherent Tunable Coupling of Superconducting Qubits."
Science, 316, 723 (2007) |
| (3) |
Yoshihara, F., Harrabi, K., Niskanen, A. O., Nakamura, Y., and Tsai, J. S.:
"Decoherence of Flux Qubits due to 1/f Flux Noise."
Physical Review Letters, 97, 167001 (2006) |
| (4) |
Astafiev, O., Pashkin, Yu. A., Nakamura, Y., Yamamoto, T., and Tsai, J. S.:
"Temperature Square Dependence of the Low Frequency 1/f Charge Noise in the Josephson Junction Qubits."
Physical Review Letters, 96, 137001 (2006) |
| (5) |
Niskanen, A. O., Nakamura, Y., and Tsai, J. S.:
"Tunable coupling scheme for flux qubits at the optimal point."
Physical Review B 73, 094506 (2006) |
| (6) |
Astafiev, O., Pashkin, Yu. A., Yamamoto, T., Nakamura, Y., and Tsai, J. S.:
"Quantum Noise in the Josephson Charge Qubit."
Physical Review Letters 93, 267007 (2004). |
| (7) |
Astafiev, O., Pashkin, Yu. A., Yamamoto, T., Nakamura, Y., and Tsai, J. S.:
"Single-shot measurement of the Josephson charge qubit."
Physical Review B 69, 180507 (2004). |
| (8) |
Yamamoto, T., Pashkin, Yu. A., Astafiev, O., Nakamura, Y., and Tsai, J. S.:
"Demonstration of conditional gate operation using superconducting charge qubits."
Nature 425, 941 (2003). |
| (9) |
Pashkin, Yu. A., Yamamoto, T., Astafiev, O., Nakamura, Y., Averin, D. V., and Tsai, J. S.:
"Quantum oscillation in two coupled charge qubit."
Nature 421, 823 (2003). |
| (10) |
Nakamura, Y., Pashkin, Yu. A., and Tsai, J. S.:
"Coherent Control of Macroscopic Quantum State in a Single-Cooper-pair Box."
Nature 398, 786 (1999). |
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Team Leader
Jaw-Shen TSAI (Ph.D.)
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