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Papers by Yoshiaki Rikitake
Foundations of Quantum Mechanics in the Light of New Technology, 2002
The dephasing of a qubit coupled with a point-contact detector is theoretically studied. We calcu... more The dephasing of a qubit coupled with a point-contact detector is theoretically studied. We calculate the time evolution of the reduced density matrix of qubit by using the perturbation expansion. We show that the dephasing rate is proportional to the temperature at zero bias-voltage, while it is proportional to the bias-voltage when the bias-voltage is large. We also evaluate the dephasing rate by using the real time renormalization group method and show that the higher order processes of the particle-hole excitation enhances dephasing of qubit.
IEICE technical report. Education technology, 2014
The present study analyzes the relationship between a teacher's evaluation of students' self-asse... more The present study analyzes the relationship between a teacher's evaluation of students' self-assessment by "Daifuku-cho," which is used for teacher-and-student interaction in PE class, and their competency improvement using PROG test scores. It turns out that there is a correlation between them, and the higher the teacher's evaluation of students' comments is, the higher the students' scores in "Competency" part of PROG test are. Compared with athletic skills, competency improvement in PE class is difficult to assess, but this study suggests that by evaluating students' self-assessment in "Daifuku-cho," we could possibly estimate their competency improvement.
IADIS INTERNATIONAL JOURNAL ON COMPUTER SCIENCE AND INFORMATION SYSTEMS, 2020
KOSENs not only try to increase students’ engineering abilities and literacy, which is the abilit... more KOSENs not only try to increase students’ engineering abilities and literacy, which is the ability to use knowledge and skills, but also their competency, which we consider is the ability to apply knowledge and skills to any problem that might arise outside the walls of school. So the present study analyzes the relationship between a teacher’s evaluation of students’ self-assessment by “Daifuku-cho,” which is used for teacher-and-student interaction in PE class, and their competency improvement using PROG test scores. The result confirmed that students’ daily self-reflection and teachers’ feedback on them are important, and the outcome of their daily self-reflection can quantitatively show the growth in their competency. In particular, we report that the interaction between students and their teacher through the use of “Daifuku-cho” enhanced their learning and also that by comparing what the students wrote in “Daifukucho,” their grades and the results of PROG test, we suggest that t...
Extended Abstracts of the 2010 International Conference on Solid State Devices and Materials, 2010
Extended Abstracts of the 2007 International Conference on Solid State Devices and Materials, 2007
We analyzed the yield and fidelity of the quantum state transfer (QST) from a photon polarization... more We analyzed the yield and fidelity of the quantum state transfer (QST) from a photon polarization qubit to an electron spin qubit in a spin-coherent photo detector consisting of a semiconductor quantum dot and a photonic cavity. We determined the optimal conditions that allow the realization of both high-yield and high-fidelity QST.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
We present photon-spin quantum-state-transfer (QST) approach. GaAs/AlGaAs-QW with g~0 showed nonl... more We present photon-spin quantum-state-transfer (QST) approach. GaAs/AlGaAs-QW with g~0 showed nonlinear B-field dependence of spin precession, suggesting photon-to-nuclei polarization transfer. 2DEG with quantum-point-contact on InGaAs/InP showed telecomwavelength-sensitive quantum transport. Efficient/high-fidelity QST conditions were also found.
Extended Abstracts of the 2010 International Conference on Solid State Devices and Materials, 2010
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
ABSTRACT
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
ABSTRACT
Physical Review B, 2005
We theoretically study decoherence of two localized spins interacting via the RKKY interaction in... more We theoretically study decoherence of two localized spins interacting via the RKKY interaction in one-, two-, and three-dimensional electron gas. We derive the kinetic equation for the reduced density matrix of the localized spins and show that energy relaxation caused by singlet-triplet transition is suppressed when the RKKY interaction is ferromagnetic. We also estimate the decoherence time of the system consisting of two quantum dots embedded in a two dimensional electron gas.
2008 Conference on Lasers and Electro-Optics, 2008
ABSTRACT
We demonstrate that a coherent superposition state of two temporally separated optical pulses, ca... more We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up/down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers a new approach for quantum interfaces between photons and electron spins.
Physical Review Letters, 2008
We demonstrate that the superposition of light polarization states is coherently transferred to e... more We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g-factors of electrons and light holes. The result encourages us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
Physical Review B, 2006
We analyzed the fidelity of the quantum state transfer (QST) from a photon-polarization qubit to ... more We analyzed the fidelity of the quantum state transfer (QST) from a photon-polarization qubit to an electron-spin-polarization qubit in a semiconductor quantum dot, with special attention to the exchange interaction between the electron and the simultaneously created hole. In order to realize a high-fidelity QST we had to separate the electron and hole as soon as possible, since the electron-hole exchange interaction modifies the orientation of the electron spin. Thus, we propose a double-dot structure to separate the electron and hole quickly, and show that the fidelity of the QST can reach as high as 0.996 if the resonant tunneling condition is satisfied.
Physical Review A, 2012
We demonstrate that a coherent superposition state of two temporally separated optical pulses, ca... more We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up-down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization-mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers an alternate approach for quantum interfaces between photons and electron spins.
Foundations of Quantum Mechanics in the Light of New Technology, 2002
The dephasing of a qubit coupled with a point-contact detector is theoretically studied. We calcu... more The dephasing of a qubit coupled with a point-contact detector is theoretically studied. We calculate the time evolution of the reduced density matrix of qubit by using the perturbation expansion. We show that the dephasing rate is proportional to the temperature at zero bias-voltage, while it is proportional to the bias-voltage when the bias-voltage is large. We also evaluate the dephasing rate by using the real time renormalization group method and show that the higher order processes of the particle-hole excitation enhances dephasing of qubit.
IEICE technical report. Education technology, 2014
The present study analyzes the relationship between a teacher's evaluation of students' self-asse... more The present study analyzes the relationship between a teacher's evaluation of students' self-assessment by "Daifuku-cho," which is used for teacher-and-student interaction in PE class, and their competency improvement using PROG test scores. It turns out that there is a correlation between them, and the higher the teacher's evaluation of students' comments is, the higher the students' scores in "Competency" part of PROG test are. Compared with athletic skills, competency improvement in PE class is difficult to assess, but this study suggests that by evaluating students' self-assessment in "Daifuku-cho," we could possibly estimate their competency improvement.
IADIS INTERNATIONAL JOURNAL ON COMPUTER SCIENCE AND INFORMATION SYSTEMS, 2020
KOSENs not only try to increase students’ engineering abilities and literacy, which is the abilit... more KOSENs not only try to increase students’ engineering abilities and literacy, which is the ability to use knowledge and skills, but also their competency, which we consider is the ability to apply knowledge and skills to any problem that might arise outside the walls of school. So the present study analyzes the relationship between a teacher’s evaluation of students’ self-assessment by “Daifuku-cho,” which is used for teacher-and-student interaction in PE class, and their competency improvement using PROG test scores. The result confirmed that students’ daily self-reflection and teachers’ feedback on them are important, and the outcome of their daily self-reflection can quantitatively show the growth in their competency. In particular, we report that the interaction between students and their teacher through the use of “Daifuku-cho” enhanced their learning and also that by comparing what the students wrote in “Daifukucho,” their grades and the results of PROG test, we suggest that t...
Extended Abstracts of the 2010 International Conference on Solid State Devices and Materials, 2010
Extended Abstracts of the 2007 International Conference on Solid State Devices and Materials, 2007
We analyzed the yield and fidelity of the quantum state transfer (QST) from a photon polarization... more We analyzed the yield and fidelity of the quantum state transfer (QST) from a photon polarization qubit to an electron spin qubit in a spin-coherent photo detector consisting of a semiconductor quantum dot and a photonic cavity. We determined the optimal conditions that allow the realization of both high-yield and high-fidelity QST.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
We present photon-spin quantum-state-transfer (QST) approach. GaAs/AlGaAs-QW with g~0 showed nonl... more We present photon-spin quantum-state-transfer (QST) approach. GaAs/AlGaAs-QW with g~0 showed nonlinear B-field dependence of spin precession, suggesting photon-to-nuclei polarization transfer. 2DEG with quantum-point-contact on InGaAs/InP showed telecomwavelength-sensitive quantum transport. Efficient/high-fidelity QST conditions were also found.
Extended Abstracts of the 2010 International Conference on Solid State Devices and Materials, 2010
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
ABSTRACT
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
ABSTRACT
Physical Review B, 2005
We theoretically study decoherence of two localized spins interacting via the RKKY interaction in... more We theoretically study decoherence of two localized spins interacting via the RKKY interaction in one-, two-, and three-dimensional electron gas. We derive the kinetic equation for the reduced density matrix of the localized spins and show that energy relaxation caused by singlet-triplet transition is suppressed when the RKKY interaction is ferromagnetic. We also estimate the decoherence time of the system consisting of two quantum dots embedded in a two dimensional electron gas.
2008 Conference on Lasers and Electro-Optics, 2008
ABSTRACT
We demonstrate that a coherent superposition state of two temporally separated optical pulses, ca... more We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up/down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers a new approach for quantum interfaces between photons and electron spins.
Physical Review Letters, 2008
We demonstrate that the superposition of light polarization states is coherently transferred to e... more We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g-factors of electrons and light holes. The result encourages us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
Physical Review B, 2006
We analyzed the fidelity of the quantum state transfer (QST) from a photon-polarization qubit to ... more We analyzed the fidelity of the quantum state transfer (QST) from a photon-polarization qubit to an electron-spin-polarization qubit in a semiconductor quantum dot, with special attention to the exchange interaction between the electron and the simultaneously created hole. In order to realize a high-fidelity QST we had to separate the electron and hole as soon as possible, since the electron-hole exchange interaction modifies the orientation of the electron spin. Thus, we propose a double-dot structure to separate the electron and hole quickly, and show that the fidelity of the QST can reach as high as 0.996 if the resonant tunneling condition is satisfied.
Physical Review A, 2012
We demonstrate that a coherent superposition state of two temporally separated optical pulses, ca... more We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up-down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization-mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers an alternate approach for quantum interfaces between photons and electron spins.