Jan 5th-8th, 2016

Yukawa Institute for Theoretical Physics, Kyoto University

"Quantum gate using superconducting composite structure (d-dot)"

Norio Fujita (Osaka Prefecture University)

A d-dot is a nano-sized composite structure that consists of a d-wave superconductor embedded in an s-wave matrix. Since the phase of the superconducting order parameter in the d-wave superconductor depends on direction [1], phase difference appears at a corner junction between d-wave and s-wave superconductors. Compensating this phase difference, a spontaneous half-quantized vortex (SHQV) appears without external magnetic fields [2]. These SHQVs break the time-reversal symmetry, there are two steady states in d-dot's. Denoting these states as "0" and "1", and controlling by an external field or current, we can use d-dot's as classic bits [3]. Since we can make superposition of these states lowering the size of the d-dot and increasing the transition probability between two states, such d-dot may work as a qubit [4]. We expect that the d-dot in quantum state can be a powerful candidate of qubit, and propose a new type quantum gate using d-dot.

1 C. C. Tsuei, J. R. Kirtley. Rev. Mod. Phys. 72, 969(2000).

2 M. Kato, T. Ishida, T. Koyama, M. Machida. Superconductors - Materials, Properties and Applications. InTech (2012) 319.

3 S. Nakajima, M. Kato, T. Koyama, M. Machida, T. Ishida, F. Nori, Physica C. 468 (2008) 759-772.

4 T. Koyama, M. Machida, M. Kato, T. Ishida, Physica C. 426-431 (2005) 1561-1565.

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