2014 Fiscal Year Annual Research Report
| Project/Area Number |
14F04330
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| Research Institution | The Institute of Physical and Chemical Research |
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Principal Investigator |
NORI FRANCO 独立行政法人理化学研究所, 創発物性科学研究センター, グループディレクター (50415262)
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| Co-Investigator(Kenkyū-buntansha) |
ZHANG Peng 独立行政法人理化学研究所, 創発物性科学研究センター, 外国人特別研究員
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| Project Period (FY) |
2014-04-25 – 2017-03-31
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| Keywords | Qubit / Spin-orbit coupling / Majorana fermions / 量子情報制御 |
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| Outline of Annual Research Achievements |
In the last fiscal year, I mainly studied the spin-orbit qubit subject to an inhomogeneous magnetic field from a multiferroic insulator as well as the Majorana states in disordered semiconductor nanowires.
We proposed a spin-orbit qubit in a nanowire quantum dot on the surface of a multiferroic insulator with a cycloidal spiral magnetic order. The spiral exchange field from the multiferroic insulator causes an inhomogeneous Zeeman-like interaction on the electron spin in the quantum dot, producing a spin-orbit qubit. The absence of an external magnetic field benefits the integration of such spin-orbit qubit into high-quality superconducting resonators. By exploiting the Rashba spin-orbit coupling in the quantum dot via a gate voltage, one can obtain an effective spin-photon coupling with an efficient on/off switching. This makes the proposed device controllable and promising for hybrid quantum circuits.
Then I studied the Majorana states in semiconductor nanowires with disordered spin-orbit coupling. I found that unlike the case of nanowires with spin-diagonal disorder where such disorder can even induce Majorana states [as reported in the literature, e.g., Phys. Rev. B 89, 144506 (2014)], the disorder in spin-orbit coupling is just detrimental to the Majorana state.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Qubits based on Majorana fermions, i.e., Majorana qubits, are attracting increasing attention. This is partly because it is suggested that they are immune to local fermionic parity-conserving perturbations which impair other qubit realizations. However, in reality, there are different kinds of disorders and actually how robust the Majorana qubits are against these disorders remains to be detailedly studied. Recently, a work, "Effects of electron scattering on the topological properties of nanowires: Majorana fermions from disorder and superlattices" [Phys. Rev. B 89, 144506 (2014)], claimed that the spin-independent disorder can preserve or even increase the topologically non-trivial phase space. That seems interesting, and is in contrast to the common imagination. Triggered by this work, I studied the effect of spin-dependent disorder on the Majorana state, to see if there is anything new or abnormal. However, unlike what was found in this work, my study revealed that the disorder in spin-orbit coupling is detrimental to the Majorana state.
After that, I started the study on Majorana qubit and its couping to the resonators. I proposed a hybrid system of a Majorana qubit and a mechanical resonator, based on a semiconductor nanowire with both an s-wave superconductor and three ferromagnetic magnets in proximity. The four Majorana bound states constitute a Majorana qubit, and their hybridization results in a coherent coupling. In our proposal, a strong coupling can be achieved. Now this work is under progress and expected to finish soon.
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| Strategy for Future Research Activity |
In this fiscal year, we plan to propose the Majorana qubit in a nanowire system and also study its coupling to the resonators, e.g., the mechanical resonators as well as the supurconducting transmission line resonators. By these studies, we intend to realize the topological qubit based on Majorana states and also achieve the manipulation on it via mechanical or electrical ways.
Further, we plan to study the multi-qubit systems. Such systems can be constituted by two or more qubits of the same type, e.g., the Majorana or the spin-orbit qubits. However, a more attractive scheme is designing a hybrid multi-qubit system, e.g., a Majorana—spin-orbit double qubit system. We hope such a hybrid system can be utilized to realize a multifunctional device to achieve both storage and manipulation of the quantum states.
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Research Products
(1 results)
