양자얽힘 전파에서 복합 양자 복제기의 역할

임의순 한국물리학회 2018 새물리 Vol.68 No.8

The main goal of quantum copying is to produce a copy of the original qubit that is as close as possible to the original state while the output state of the original qubit is minimally distributed. In this paper, we investigate how quantum entanglement can be broadcast to two distant partners via only local quantum copying by using a hybrid cloning machine that is composed of a linear combination of pre-existing quantum cloning machines. The initial entangled state is shared by two distant parties, and the two sides each use a hybrid cloning machine to replicate their shared quantum state. In the case of using a hybrid cloning machine, we study how the quantum entanglement between remote replicas propagates according to the complexity of the hybrid cloning machine and the degree of their influence by investigating the Hillbert-Schmidt (HS) distance and the inseparable regions. As a result, quantum entanglement was found to be very sensitive to the influence of the cloning machines, and the sensitivity was found to be in the order of Meridian Phase-Covariant (MPC) > Equtorial Phase-Covariant (EPC) > Universal Quantum Cloning Machine (UQCM). Therefore, the hybrid cloning machine of a Buzek-Hillery (BH) type and an equatorial phase covariate QCM are advantageous for maintaining quantum entanglement. 양자복제의 목적은 복제본은 원래의 상태와 가장 가까운 반면 원본 큐빗의 출력상태는 최소로 왜곡되는 양자 복제본을 만드는 것이다. 이 논문에서 우리는 기존의 두 양자 복제기의 선형결합으로 구성된 복합 양자복제기를 사용하여 처음의 양자 얽힌 상태가 복제 후 복제 상태들에 어떻게 전파하는지를 조사하였다. 처음의 얽힌 상태는 서로 멀리 떨어져 있는 양측이 공유하고, 양측은 자신이 공유한 양자 상태를 각각 복합 양자복제기로 복제한다. 복합 양자복제기를 사용하는 경우 복합 복제기의 복합도와 복제기의 영향도에 따라 원격 복제본들 사이의 양자얽힘이 어떻게 전파하는지를 Hillbert-Schmidt (HS) 거리와 분리 불가능영역 조사를 통하여 연구하였다. 그 결과 양자얽힘 상태는 복제기의 영향도에 매우 민감하여, 그 민감성은 Meridian Phase-Covariant (MPC) > Equtorial Phase-Covariant (EPC) > Universal Quantum Cloning Machine (UQCM) 순임을 알았다. 따라서 양자얽힘을 유지하는데는 Buzek-Hillery (BH) 유형 복제기와 적도위상공변 복제기의 복합 복제기가 유리하다.

Novel Class of Entanglement-Assisted Quantum Codes with Minimal Ebits

Cao Dong,Song Yaoliang 한국통신학회 2013 Journal of communications and networks Vol.15 No.2

Quantum low-density parity-check (LDPC) codes based on the Calderbank-Shor-Steane construction have low encoding and decoding complexity. The sum-product algorithm(SPA) can be used to decode quantum LDPC codes; however, the decoding performance may be significantly decreased by the many four-cycles required by this type of quantum codes. All four-cycles can be eliminated using the entanglement-assisted formalism with maximally entangled states (ebits). The proposed entanglement-assisted quantum error-correcting code based on Euclidean geometry outperform differently structured quantum codes. However, the large number of ebits required to construct the entanglement-assisted formalism is a substantial obstacle to practical application. In this paper, we propose a novel class of entanglement-assisted quantum LDPC codes constructed using classical Euclidean geometry LDPC codes. Notably, the new codes require one copy of the ebit. Furthermore,we propose a construction scheme for a corresponding zigzag matrix and show that the algebraic structure of the codes could easily be expanded. A large class of quantum codes with various code lengths and code rates can be constructed. Our methods significantly improve the possibility of practical implementation of quantum error-correcting codes. Simulation results show that the entanglement-assisted quantum LDPC codes described in this study perform very well over a depolarizing channel with iterative decoding based on the SPA and that these codes outperform other quantum codes based on Euclidean geometries.

Novel Class of Entanglement-Assisted Quantum Codes with Minimal Ebits

Dong, Cao,Yaoliang, Song The Korea Institute of Information and Commucation 2013 Journal of communications and networks Vol.15 No.2

Quantum low-density parity-check (LDPC) codes based on the Calderbank-Shor-Steane construction have low encoding and decoding complexity. The sum-product algorithm(SPA) can be used to decode quantum LDPC codes; however, the decoding performance may be significantly decreased by the many four-cycles required by this type of quantum codes. All four-cycles can be eliminated using the entanglement-assisted formalism with maximally entangled states (ebits). The proposed entanglement-assisted quantum error-correcting code based on Euclidean geometry outperform differently structured quantum codes. However, the large number of ebits required to construct the entanglement-assisted formalism is a substantial obstacle to practical application. In this paper, we propose a novel class of entanglement-assisted quantum LDPC codes constructed using classical Euclidean geometry LDPC codes. Notably, the new codes require one copy of the ebit. Furthermore, we propose a construction scheme for a corresponding zigzag matrix and show that the algebraic structure of the codes could easily be expanded. A large class of quantum codes with various code lengths and code rates can be constructed. Our methods significantly improve the possibility of practical implementation of quantum error-correcting codes. Simulation results show that the entanglement-assisted quantum LDPC codes described in this study perform very well over a depolarizing channel with iterative decoding based on the SPA and that these codes outperform other quantum codes based on Euclidean geometries.

Entanglement Dynamics of Multipartite States under an XY Quantum-Critical Environment

Xiao San Ma,An Min Wang 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6

By using negativity as an entanglement measure, we investigate the entanglement dynamics of multipartite quantum states under an XY quantum environment, which can exhibit a quantum phase transition. From the results, we find that the time evolution of multipartite quantum states depends not only on the size of the system and the quantum states of concern but also on the degrees of freedom of the environment, the anisotropy, and the transverse magnetic field of the environment. Especially, we find that the entanglement decay will be enhanced by the quantum phase transition of the environment under weak coupling. By using negativity as an entanglement measure, we investigate the entanglement dynamics of multipartite quantum states under an XY quantum environment, which can exhibit a quantum phase transition. From the results, we find that the time evolution of multipartite quantum states depends not only on the size of the system and the quantum states of concern but also on the degrees of freedom of the environment, the anisotropy, and the transverse magnetic field of the environment. Especially, we find that the entanglement decay will be enhanced by the quantum phase transition of the environment under weak coupling.

Progress of quantum entanglement in a trapped-ion based quantum computer

Yum Dahyun,Choi Taeyoung 한국물리학회 2022 Current Applied Physics Vol.41 No.-

In recent years, there have been significant progress toward building a practical quantum computer, demonstrating key ingredients such as single-qubit gates and a two-qubit entangling gate. Among various physical platforms for a potential quantum computing processor, a trapped-ion system has been one of the most promising platforms due to long coherence times, high-fidelity quantum gates, and qubit connectivity. However, scaling up the number of qubits for a practical quantum computing faces a core challenge in operating high-fidelity quantum gates under influence from neighboring qubits. In particular, for the trapped-ion system, unwanted quantum crosstalk between qubits and ions’ quantum motional states hinder performing high-fidelity entanglement as the number of ions increases. In this review, we introduce a trapped-ion system and explain how to perform single-qubit gates and a two-qubit entanglement. Moreover, we mainly address theoretical and experimental approaches to achieve high-fidelity and scalable entanglement toward a trapped-ion based quantum computer.

복합 양자 복제기에서 양자얽힘 전파

임의순,신용진 한국물리학회 2015 새물리 Vol.65 No.10

We investigated how the quantum entanglement share, after coping by using a hybrid cloning machine, can be broadcast to two distant partners via only local quantum copying. The hybrid quantum cloning machine is composed of linear combination of pre-existing quantum cloning machine which is state dependent and state independent (or universal) quantum cloning machine. In this work, we investigate the problems of two types: (1) hybrid of WZ and BH universal quantum cloning machine and (2) hybrid of BH universal and BH type state dependent quantum cloning machine. We confirmed that a hybrid cloning machine can be used to broadcast partially to remote pairs with the hybrid ratio of the hybrid cloner. Also, a universal quantum cloning machine, in which the qualities of the clones are independent of the input states, can optimally broadcast quantum entanglement. However, the entanglement cannot be preserved by local copying. 복합양자복제기를 사용하여 서로 멀리 떨어져 있는 양측에 각각 한곳 양자복제를 하였을 때, 복제 후 양자얽힘이 어떻게 전파하는지를 조사하였다. 복합양자복제기는 상태독립 (또는 범용) 양자복제기와 상태의존 양자복제기인 기존의 두 양자복제기의 선형 결합으로 구성된다. 이 논문에서 우리는 (1) WZ 양자복제기와 BH 범용 양자복제기의 결합, (2) BH 범용 양자복제기와 BH 유형 상태의존 양자복제기의 결합의 두 유형의 문제를 다룬다. 복합 양자복제기를 사용하여 한곳 복제만을 하는 경우 복합 복제기의 복합도에 따라 원격 복제본들 사이의 양자얽힘이 어떻게 전파하는지 명확하게 알 수 있었다. 또한, 복제의 품질이 입력상태에 무관한 범용 양자복제기를 사용하는 경우에 양자얽힘이 가장 잘 전파됨을 확인하였다. 이때 한곳 복제에서 양자얽힘은 보존되지 않는다.

Entanglement Dynamics of Electron Spins in Quantum Dots Under a Nonuniform Magnetic Field

Feng-Xue Zhou,Yi-Hong Qi,Yue-Ping Niu,Shang-Qing Gong,Jun Qian,Ting Yu,Franco Nori 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.8

We investigate entanglement of two coupled electron spins in quantum dots (QDs) in the presence of an inhomogeneous magnetic field. The great effects of the inhomogeneous field are discussed for the dynamics of entanglement. It is shown that due to the system's symmetry, the inhomogeneity of the field does not affect the evolution of entanglement for Φ-type Bell state, while it plays a key role for Ψ-type Bell state. For the maximal entangled Bell states, the field is positive for the entanglement dynamics. The mean field can increase the entanglement revival for Φ-type Bell state while the inhomogeneous field can promote the entanglement revival for Ψ-type Bell state. For the unentangled initial states, the field is destructive for the entanglement generation induced by the coupling of the two spins.

≪주역≫철학사상과 양자역학 철학적개념의 유사성 고찰 -≪주역≫철학사상의 과학성 傍證-

최송현 동아인문학회 2022 동아인문학 Vol.59 No.-

This paper aims to study the philosophy of Yijing in terms of quantum physics to corroborate scientific characteristics of Yijing, and to establish standards of conducting research from an active and pluralistic perspective for changing perceptions toward Yijing by discussing the lessons learned from research about modern science and quantum physics. Yijing symbolizes the principle of change in everything in the universe with “Image・Language・Stroke・Number” and classify them into 64 categories, so it has been studied in various academic fields. Physics is the foundation of modern science, observing types of components in the universe and its kinetic energy. The two studies have different backgrounds and approaches but have similar ultimate goals and the nature of philosophical idea. For example, quantum physics proposed theories of “quantum jump, uncertainty and complementarity principle and quantum entanglement” based on the Big Bang theory that ‘if something don't move, it extinct’. Similarly, the meaning of “if there is a place to go, it is beneficial” in Yijing is the same concept as the “kinetic energy” in quantum physics. That is, Yijing and quantum physics are scientific theories with a common nature in that they share the philosophical concept of “movement (change).” Nevertheless, there have been cases until recently in the institutional and social leadership of the East that devalue the philosophy of Yijing as “intuitive and unscientific fortune-telling.” However, in Western Europe, there is an increasing tendency to recognize the scientific characteristics in Yijing and overcome and supplement the limitations of modern science through Yijing. Therefore, this paper tries to examine the similar philosophical concepts between Yijing and quantum physics, and establish a framework for proving scientific characteristics, changing perception, and prompting research of Yijing based on the lessons learned from research about modern science and quantum physics. 본 소고(小考)는 ≪주역≫의 철학사상과 양자역학 철학적 개념의 유사성을 연구하여 ≪주역≫ 철학사상의 ‘과학성’을 방증하고, 현대과학과 양자역학의 연구 현황을 통해 얻은 교훈을 근거로 ≪주역≫ 철학사상에 대한 인식 태도의 전환과 활발하고 다원적인 관점의 연구 활동 방안을 마련하고자 한다. ≪주역≫은 우주 만물을 象・辭・爻・數에 부호모형의 64괘로 ‘取象比類’하고 학문의 각 분야에서 64괘의 연구를 하고 있다. 물리학(physics)은 현대과학의 근본으로 우주 만물을 이루고 있는 구성요소의 유형과 운동에너지를 관찰 연구하는 학문이다. ≪주역≫과 양자역학 연구는 출발 시점의 時・空間과 접근방법은 달리하고 있으나, 연구의 궁극적 지향점과 담겨있는 철학적 사고의 본질은 유사하다. 양자역학은 원자핵(+) 주변을 움직이는 전자(-)와 중성자의 위치나 운동량을 관찰하고 그들 상호 관계를 분석하여 ‘양자도약, 불확정성과 상보성, 양자얽힘’ 등의 이론을 발표하였다. ≪주역≫ 철학사상에 ‘갈 곳이 있으면 이롭다’라는 변화에 의한 ‘항상 됨’의 의미는, 양자역학의 ‘운동에너지’와 같은 理致이다. ≪주역≫의 철학사상과 양자역학의 철학적 개념은 ‘운동 즉 변화’라는 공통의 본성을 지닌 과학성을 지니고 있다. 그러나 동양의 제도권이나 사회 지도층에서는 ≪주역≫ 철학사상을 ‘직관적이며 비과학적인 점술’로 평가 절하하는 사례가 최근에도 발생하고 있다. 그런데도 과학 종주국인 서구에서는≪주역≫ 철학사상의 본질 속에 담겨있는 ‘과학성’을 인정하고 자연과학의 한계와 문제점을 ≪주역≫ 철학사상의 연구를 통해 극복하고 보완해 가는 경향이 증가하고 있다. 본 소고는 ≪주역≫ 철학사상과 양자역학의 철학적 개념이 유사함을 고찰하고 양자역학 연구 현황분석에서 얻은 교훈을 거울삼아 ≪주역≫ 철학사상의 ‘과학성 방증, 인식의 전환, 연구의 활성화’ 방안을 마련코자 한다.

0과 1의 해석학 ―수학, 디지털 및 양자정보, 그리고 주역과 노장

오태석 ( Oh Tae-suk ) 한국중국어문학회 2018 中國文學 Vol.97 No.-

This paper mainly put emphasis on the concept of ‘ambiguity’ and ‘ambivalence’, not on ‘clarity’ in regard to information theory. The specific contents are about the humanistic implies of the numbers ‘0 and 1’. I describe it into three parts as follows: ① Many interpretations of humanistic math about ‘0 and 1’ which could be extended to the circle and wave in TaiJI(太極) and its center line and its augural meaning of differential equation; probability; set in regard to George Cantor’s diagonal argument; and exponential function and log function which are related with the concept of information bit. ② A comparison of information theory about ‘0 and 1’ in digital computer’s bit with quantum computer’s qbit. ③ Mathematical semiotics of Yin and Yang in Book of Change(Yi-Jing), and Laozhuang’s view of ‘liangxing(兩行)’, i.e. going two-ways simultaneously from the aspect of information theory. In this paper I maintain 3 points as follows: ⓐ Similarity of ambivalence(兩價性) between 0 that includes nothing and infinity and concept of ‘Wu’(無) in Laozi(老子). ⓑ digital computer’s operating system is alternative algorithm i.e. {0/1}. Meanwhile quantum computer is simultaneously ambivalent taking algorithm i.e. {0&1}, which is based on quantum superposition and quantum entanglement. In other words, digital computer is based on the way of optional choice, and quantum computer runs in two different ways simultaneously. I think quantum computer’s operating system is much similar to the process of “Yang from Yin(陰中陽)” and “Yin from Yang(陽中陰)” in YiJing(易經), which is operated in intrinsically mutual complementary way. ⓒ For hundreds of years Western thoughts made much of rational clarity, and in result the thoughts of ambivalence’ (兩價性) in East Asian traditional thoughts are neglected relatively. I think from the impact of Einstein’s Relative Theories and Quantum Mechanics in early decades of 20th century, people start ringing that rational clarity is not always superior to ambivalence and ambiguity, especially in modern science. In this paper I considered the matter of humanistic implies about ‘0 and 1’ especially from information theory. And I would like to evoke the changing situation in recent recognition on ‘ambiguity’ or ‘ambivalence’, unlike past centuries.

Manipulating the Sudden Death of Entanglement in Two-qubit Atomic Systems

Mahmood Irtiza Hussain,Rabia Tahira,Manzoor Ikram 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.41

We investigate the entanglement dynamics of a general two-qubit system in a noisy environment presenting analytical descriptions of the time evolution of entanglement having some unitary operations after its evolution in dissipative environments. We show that quantum gates (unitary operators) and bath switching can change the subsequent dynamics of entanglement. For this purpose, we consider σ_x and bath switching operations that change the disentanglement time from finite to infinite.