Browsing by Author "Nakahara, Mikio"

Now showing 1 - 3 of 3
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    Spin-selective electron transfer in a quantum dot array
    (2018-01-17) Masuda, Shumpei; Tan, Kuan Yen; Nakahara, Mikio; Department of Applied Physics; Quantum Computing and Devices; Centre of Excellence in Quantum Technology, QTF; Shanghai University
    We propose a spin-selective coherent electron transfer in a silicon quantum dot array. Oscillating magnetic fields and temporally controlled gate voltages are utilized to separate the electron wave function into different quantum dots depending on the spin state. We introduce a nonadiabatic protocol based on π pulses and an adiabatic protocol which offer fast electron transfer and robustness against the error in the control-field pulse area, respectively. We also study a shortcut-to-adiabaticity protocol which compromises these two protocols. We show that this scheme can be extended to multielectron systems straightforwardly and used for nonlocal manipulations of electrons.
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    Theoretical Study on Spin-Selective Coherent Electron Transfer in a Quantum Dot Array
    (MDPI AG, 2019-12-22) Masuda, Shumpei; Tan, Kuan; Nakahara, Mikio; Department of Applied Physics; Quantum Computing and Devices; Centre of Excellence in Quantum Technology, QTF; Tokyo Medical and Dental University; Shanghai University
    Recently, we proposed the spin-selective coherent electron transfer in a silicon-quantum-dot array. It requires temporal tuning of two pulses of an oscillating magnetic field and gate voltage control. This paper proposes a simpler method that requires a single pulse of oscillating magnetic field and gate voltage control. We examined the robustness of the control against the error in the pulse amplitude and the effect of the excited states relaxation to the control efficiency. In addition, we propose a novel control method based on a shortcuts-to-adiabaticity protocol, which utilizes two pulses but requires temporal control of the pulse amplitude for only one of them. We compared their efficiencies under the effect of realistic pulse amplitude errors and relaxation.
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    Three-dimensional skyrmions in spin-2 Bose-Einstein condensates
    (2018) Tiurev, Konstantin; Ollikainen, Tuomas; Kuopanportti, Pekko; Nakahara, Mikio; Hall, David S.; Möttönen, Mikko; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Computing and Devices; Shanghai University; Amherst College; University of Helsinki
    We introduce topologically stable three-dimensional skyrmions in the cyclic and biaxial nematic phases of a spin-2 Bose-Einstein condensate. These skyrmions exhibit exceptionally high mapping degrees resulting from the versatile symmetries of the corresponding order parameters. We show how these structures can be created in existing experimental setups and study their temporal evolution and lifetime by numerically solving the three-dimensional Gross-Pitaevskii equations for realistic parameter values. Although the skyrmions are eventually destroyed due to the instability of the underlying magnetic phase, their lifetimes are found to be long enough for experimental detection.