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タイトル:  Study on the bunchingantibunching nature of current noise cross correlation in ultrasmall solid state entangler with ohmic dissipation based on the nonperturbative SchwingerKeldysh scheme theory for full counting statistics 
その他のタイトル:  シュウィンガーケルディッシュ形式の非摂動論的完全計数統計理論に基づいたオーミック散逸を持つ極微細個体量子もつれ構造における電流雑音の交差相関のバンチング性に関する研究 
著者:  金井, 友希美 
著者（別表記） :  Kanai, Yukimi 
著者読み:  かない, ゆきみ 
キーワード:  SchwingerKeldysh scheme theory; full counting statistics; ohmic dissipation; ultrasmall solid state entangler; current noise cross correlation; bunchingantibunching nature 
発行日:  2018年 3月23日 
引用:  奈良女子大学博士論文, 博士（理学）, 博課 甲第639号, 平成30年3月23日学位授与 
抄録:  In this thesis, we propose the the nonperturbative theory for full counting statistics
(FCS) in solid state entangler (SSE) based on NambuGor’kov and SchwingerKeldysh
field theoretical nonequilibrium method. Based on the theory we study the currents
and cross correlation of the current noise of SSE to get the further understanding
of physics of quantum entanglement. The theory can be applicable to the transport
properties in the region where Coulomb blockade and Andreev reflection coexist,
since tunneling processes are taken into account nonperturbatively in the presence of
arbitrarily large charging effect as well as electromagnetic environment effect. Concerning
the latter, we treat SSE with ohmic resistance phenomenologically in the
spirit of CaldeiraLeggett theory.
The SSE considered is a coupled ultrasmall double tunnel junction, structure of
which consists of a common superconducting electrode/normalconducting left and
right ultrasmall central electrodes (islands)/normalconducting left and right drains.
Each of islands are capacitively coupled with gate electrodes to control tunneling. We
call the SSE double S/N/N capacitively coupled single electron transistors (double
S/N/N CSET). This kind of SSE is called the Cooper pair splitter (CPS) in general.
Based on the theory, we derive explicit expression for cumulant generating function
(CGF) for FCS. Explicit expressions for the currents and cross correlation of current
noise for the double S/N/N CSET are obtained as the first and second cumulants
from CGF, respectively. Since we are interested in extracting and controlling quantum
entanglement information by the charging effect, we mainly focus our attention on
the study of SSE with U < Δ (U: charging energy, Δ: energy gap of superconductor)
so that sufficiently wide superconducting subgap region can be expected.
We show that, in the subgap region there are three kinds of currents due to the
direct Andreev reflection (dAR), crossed Andreev reflection (cAR) and elastic cotunneling
(EC). Each of the currents show Coulomb blockade related phenomena
(Coulomb gaps, Coulomb staircases, and Coulomb oscillations) due to the charging
effect.
Since contribution to the cross correlation of current noise SLR(0) comes from
currents due to cAR and EC in subgap region, SLR(0) is strongly influenced by the
charging effect. It is shown that SLR(0) is always positive (bunching correlation)
if two CSETs are biased symmetrically. The bunching correlation is not genuine
one (antibunching correlation) peculiar to the normal fermion flow. It is the direct
consequence of the fermion flow with quantum entanglement. SLR(0) also shows
bunchingantibunching crossover followed by restoration of bunching correlation as
bias voltage increases; i.e., SLR(0) becomes negative only in a narrow window of bias
voltage as far as bias condition for two CSETs is not so asymmetric enough. As the
asymmetry in bias condition becomes sizable, SLR(0) shows bunchingantibunching
crossover only and never shows the restoration of bunching correlation.
We also show that the ohmic resistance strongly influences on SLR(0), partly because
of increase in Coulomb Gap of cAR current, and partly because of decrease in
magnitude of cAR current due to the decoherence by ohmic dissipation.
We propose the method of extraction and control of quantum entanglement information
by the ferromagnetic ordering. We consider double S/F/N CSET, structure of
which is the one with the nonmagnetic islands of double S/N/N CSET is replaced by
ferromagnetic islands. It is shown that only cAR current (EC current) contributes to
SLR(0) if the half metal ferromagnetic islands are employed as antiparallel (parallel)
alignment.
Theoretical predictions stated above are made for the first time in this study and
the results lead us to the new stage of the study on bunchingantibunching nature of
current noise cross correlation in the presence of quantum entanglement. 
URI:  http://hdl.handle.net/10935/4719 
出現コレクション:  博士学位論文

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http://hdl.handle.net/10935/4719

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