j−1=2i ↦ j1=2i becomes much more relevant than theenergy emission process j−1=2i ↦ j−3=2i.
Heat engine based on superabsorption.—Here, we
describe our protocol of the quantum-enhanced heat engine
based on superabsorption (see Fig. 1). The N-qubit system
is a working medium in our scheme. We employ a hightemperature bath and a low-temperature bath. The inverse
概要
temperature and cavity frequency of the high(low)量子輸送研究室では、量子力学に立脚した非平衡現象のC
temperature bath are βH ðβC Þ and ωHc ðωc Þ, respectively.
解明、また量子力学を用いた新しい情報処理である量子The initial state ρ̂S ð0Þ
P is diagonal in the Dicke states
情報科学に取り組んでいます。特に以下のテーマに興味
fjMigM as ρ̂S ð0Þ ¼ M pM ð0ÞjMihMj. A cycle of theheat engine consists of four strokes as follows: Stroke 1:を持って研究をしています。
with a high-temperature bath. The
半導体を中心としたナノ・メゾスコピック系の電気電•Thermalization
N-qubit system is coupled with a high-temperature bath
βH動、熱伝導、ナノメカニクス
for a period τH . During this process, the qubits areH
古典・量子系の非平衡ダイナミクス、非平衡統計•resonantwith the cavity as ωHc ¼ ωA , and the energy
the Dicke state jMi is given by EH•of量子ドット中の電子スピンを用いた量子情報処理
M ¼H2
量子計算の理論的基礎、量子エラー訂正、量子通信
A þ M Ω. The dynamics of this thermalization stroke•Mω

量子輸送研究室(1) Thermalization(superabsorption)(3) Thermalization(2) Quench(superradiance)(4) Quench
FIG. 1. 量子効果を用いてパワーと効率の両立を実Schematic of protocol for heat engine based on superabsorption. N qubits interact
with a cavity coupled with a thermal
現した量子熱機関
bath. This configuration is useful for tailoring the properties ofthe environment for the qubits. By repeated thermalization of theCCCCcondition ωc ¼ ωA is assumed. The dynamics
P in this stroke

is described by ρ̂S ðτH Þ ↦ ρ̂S ðτÞ ¼ M pM ðτÞjMihMj
教員：都倉康弘、吉田恭(τ ¼ τH þ τC ). Similar to Stroke
1, a heat output QC toP
URL：https://www.u.tsukuba.ac.jp/~tokura.yasuhiro.ft/
thebath is defined as QC ¼ M ECM ½pM ðτH Þ − pM ðτÞ&.
連絡先：tokura.yasuhiro.ft@u.tsukuba.ac.jp
Stroke4: Quenching of the qubit frequency ωCA ↦ ωHA.
After decoupling all the qubits from the heat bath βC , thequbit
frequency is simultaneously changed from ωCA to ωH
微小磁石を活用した電子スピン操作
A.
Again,
we assume that we can ignore the quenching time
微小磁石を配置することにより空間的に変化する磁束密for this stroke. For the same reason as that in the case of度を実現すると、ゲート電圧に印加する電圧を高速に制Stroke 2, the quantum state remains in ρ̂S ðτÞ during this
御するだけで電子スピンをコヒーレントに制御すること
stroke,andinput W in to the system is defined
P a work
HCができることを提案し、実験的に実証しました。
as Win ¼M ðEM − EM ÞpM ðτÞ.
We define the efficiency η and power output P of the heatengine cycle asη¼W ext;
QH

P¼W ext;τð5Þ

where W ext ¼ W out − W in denotes the extractable work. We
introduce an efficiency deficit as Δη ¼ ηC − η, where ηC ¼
1 − βH =βC is the Carnot efficiency.
Now, we explain the choice of parameters. We set thethermalization periods as τH ¼ ϵ=ða1=2 ΓH↓
1=2 Þ and τC ¼ϵ=ða1=2 ΓC↓
1=2 Þ, where ϵ denotes a positive dimensionlessconstant. Then, the cycle period τ ¼ τH þ τC scales asτ ¼ ΘðN −2 Þ. For the subsequent analytical discussion, ϵ
量子秘匿測定should be much smaller than one so that higher-order terms
2
Oðϵ「量子もつれ」状態を活用することにより、複数の測定
Þ canPbe ignored. Moreover, we choose the initial state者のなかから測定者を同定されることなく、測定結果をρ̂S ð0Þ
¼ M pM ð0ÞjMihMj as送る方法を提案しました。
2;
ð6Þ
p−1=2 ð0Þ ¼−βH ωH−βC ωCAA
þe2þe
wherepð0Þ ¼ 1 − pð0Þandp ð0Þ ¼ 0for