Relevant bibliographies by topics / TWO-QUBIT SYSTEM

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers
  5. Reports

Academic literature on the topic 'TWO-QUBIT SYSTEM'

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Published: 11 September 2023

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Journal articles on the topic "TWO-QUBIT SYSTEM"

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Zhao, Chao-Ying, Qi-Zhi Guo, and Wei-Han Tan. "A simple entanglement criterion of two-qubit system." International Journal of Modern Physics B 33, no. 18 (July 20, 2019): 1950197. http://dx.doi.org/10.1142/s0217979219501972.

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We present a novel method to judge the entanglement of two-qubit system, the density matrix of a two-qubit system can be constituted by the principle density matrix [Formula: see text] and the separable density matrices [Formula: see text]–[Formula: see text]. The necessary and sufficient conditions for the two-qubit system, the three involved coefficients p [Formula: see text] 0, p [Formula: see text] 0, p [Formula: see text] 0, and the principal density matrix [Formula: see text] being separable, then the two-qubit system is separable, otherwise the two-qubit system is entangled. Finally, the criterion for several known density matrices have been verified in this way.
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Kato, Akihito, and Yoshitaka Tanimura. "Quantum heat transport of a two-qubit system: Interplay between system-bath coherence and qubit-qubit coherence." Journal of Chemical Physics 143, no. 6 (August 14, 2015): 064107. http://dx.doi.org/10.1063/1.4928192.

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Khalil, E. M., and A. B. A. Mohamed. "Dynamics of entanglement and population inversion of two qubits in a hybrid nonlinear system." Modern Physics Letters A 36, no. 06 (January 15, 2021): 2150037. http://dx.doi.org/10.1142/s0217732321500371.

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An analytical solution is obtained when the Kerr medium and Stark shift are considered as nonlinear interaction terms to the system containing two-qubit and two-mode electromagnetic field from the parametric amplifier. Dynamics of the population inversion, cavity–qubit and qubit–qubit entanglements are analyzed under the unitary cavity–qubit interaction, the Kerr medium and the Stark shift. The population inversion of a qubit presents periodic revivals and collapses. The results show that the entanglement and the population inversion as well as the inversion have the same stable intervals, that is, the collapse intervals. It is found that the Kerr medium and the Stark shift may lead to reduction of the periods and the amplitudes of the population inversion and the cavity–qubit/qubit–qubit entanglement. The deteriorated qubit–qubit/cavity–qubit entanglement and the population inversion, due to the Kerr medium, may be increased by increasing the Stark shift and vice versa.
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Zhao, Chao-Ying, Qi-Zhi Guo, and Wei-Han Tan. "A novel entanglement criterion of two-qubit system." International Journal of Modern Physics B 34, no. 05 (February 17, 2020): 2050022. http://dx.doi.org/10.1142/s0217979220500228.

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The “separability problem” in quantum information theory is a quite important and well-known hard problem. The low-dimensional system satisfies the PPT criterion. However, the high-dimensional system problem has been shown to be NP-hard problem. In general, it is very difficult to find the analytic solution of the density matrix for the high-dimensional system. Therefore, getting an analytic solution for two-qubit system is an interesting and useful problem. We propose a novel criterion for separability and entanglement-verification of two-qubit system. We expressed the density matrix by a sum of a principal density matrix and six separable density matrices. The necessary and sufficient conditions for the two-qubit system include that if the four involved coefficients [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and the principal density matrix [Formula: see text] are separable, then the two-qubit system is separable, otherwise the two-qubit system is entangled. Finally, our criterion results in a totally different conclusion compared to Horodecki’s criterion. We believe that the new criterion is more stringent than existing PPT methods.
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ADHIKARI, SATYABRATA. "ENTANGLEMENT AND TELEPORTATION IN BIPARTITE SYSTEM." International Journal of Quantum Information 08, no. 07 (October 2010): 1153–67. http://dx.doi.org/10.1142/s0219749910006411.

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We present a mathematical formulation of old teleportation protocol (original teleportation protocol introduced by Bennett et al.) for mixed state and study in detail the role of mixedness of the two-qubit quantum channel in a teleportation protocol. We show that maximally entangled mixed state described by the density matrix of rank-4 will be useful as a two-qubit teleportation channel to teleport a single qubit mixed state when the teleportation channel parameter p1 > 1/2. Also we discuss the case when p1 ≤ 1/2.
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FRYDRYSZAK, ANDRZEJ M. "NILPOTENT QUANTUM MECHANICS." International Journal of Modern Physics A 25, no. 05 (February 20, 2010): 951–83. http://dx.doi.org/10.1142/s0217751x10047786.

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We develop a generalized quantum mechanical formalism based on the nilpotent commuting variables (η-variables). In the nonrelativistic case such formalism provides natural realization of a two-level system (qubit). Using the space of η-wavefunctions, η-Hilbert space and generalized Schrödinger equation we study properties of pure multiqubit systems and also properties of some composed, hybrid models: fermion–qubit, boson–qubit. The fermion–qubit system can be truly supersymmetric, with both SUSY partners having identical spectra. It is a novel feature that SUSY transformations relate here only nilpotent object. The η-eigenfunctions of the Hamiltonian for the qubit–qubit system give the set of Bloch vectors as a natural basis.
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MAZIERO, JONAS, and ROBERTO M. SERRA. "CLASSICALITY WITNESS FOR TWO-QUBIT STATES." International Journal of Quantum Information 10, no. 03 (April 2012): 1250028. http://dx.doi.org/10.1142/s0219749912500281.

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In the last few years one realized that if the state of a bipartite system can be written as ∑i,j pij|ai〉〈ai| ⊗ |bj〉〈bj|, where {|ai〉} and {|bj〉} form orthonormal basis for the subsystems and {pij} is a probability distribution, then it possesses at most classical correlations. In this article we introduce a nonlinear witness providing a sufficient condition for classicality of correlations (absence of quantum discord) in a broad class of two-qubit systems. Such witness turns out to be necessary and sufficient condition in the case of Bell-diagonal states. We show that the witness introduced here can be readily experimentally implemented in nuclear magnetic resonance setups.
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Ntalaperas, Dimitrios, and Nikos Konofaos. "Encoding Two-Qubit Logical States and Quantum Operations Using the Energy States of a Physical System." Technologies 10, no. 1 (December 22, 2021): 1. http://dx.doi.org/10.3390/technologies10010001.

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In this paper, we introduce a novel coding scheme, which allows single quantum systems to encode multi-qubit registers. This allows for more efficient use of resources and the economy in designing quantum systems. The scheme is based on the notion of encoding logical quantum states using the charge degree of freedom of the discrete energy spectrum that is formed by introducing impurities in a semiconductor material. We propose a mechanism of performing single qubit operations and controlled two-qubit operations, providing a mechanism for achieving these operations using appropriate pulses generated by Rabi oscillations. The above architecture is simulated using the Armonk single qubit quantum computer of IBM to encode two logical quantum states into the energy states of Armonk’s qubit and using custom pulses to perform one and two-qubit quantum operations.
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von Kugelgen, Stephen, Matthew D. Krzyaniak, Mingqiang Gu, Danilo Puggioni, James M. Rondinelli, Michael R. Wasielewski, and Danna E. Freedman. "Spectral Addressability in a Modular Two Qubit System." Journal of the American Chemical Society 143, no. 21 (May 20, 2021): 8069–77. http://dx.doi.org/10.1021/jacs.1c02417.

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Tzemos, A. C., G. Contopoulos, and C. Efthymiopoulos. "Bohmian trajectories in an entangled two-qubit system." Physica Scripta 94, no. 10 (August 7, 2019): 105218. http://dx.doi.org/10.1088/1402-4896/ab2445.

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Dissertations / Theses on the topic "TWO-QUBIT SYSTEM"

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Ruelas, Paredes David Reinaldo Alejandro. "Quantum state tomography for a polarization-Path Two-Qubit optical system." Master's thesis, Pontificia Universidad Católica del Perú, 2019. http://hdl.handle.net/20.500.12404/14117.

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En el área de los sistemas cuánticos abiertos, es común encontrar experimentos y modelos teóricos en los que el sistema de interés es representado por un cubit (sistema de dos niveles) y el entorno por otro cubit pese a que un entorno realista debería contener muchos más grados de libertad que el sistema con el que interactúa. No obstante, la simulación de entornos mediante un cubit es usual en la óptica cuántica, como también lo es la realización de evoluciones de sistemas de dos cubits. Los procedimientos utilizados para caracterizar los estados cuánticos producidos en el laboratorio son conocidos como tomografía de estados cuánticos. Existen algoritmos de tomografía para distintos tipos de sistemas. En esta tesis presentamos un dispositivo interferométrico que permite generar y hacer tomografía a un estado puro de un sistema de dos cubits: polarización y camino de propagación de la luz. Nuestra propuesta requiere 18 mediciones de intensidad para caracterizar cada estado. Ponemos a prueba nuestra propuesta en un experimento y contrastamos sus resultados con las predicciones teóricas.
In the field of open quantum systems, we usually find experiments and models in which the system is represented by a qubit (two-level system) and its environment by another qubit even though a realistic environment should contain many more degrees of freedom than the system it interacts with. However, these types of simulations are common in quantum optics, as are models of two-qubit system evolutions. The procedures that characterize quantum states produced in a laboratory are known as quantum state tomography. Standard tomography algorithms exist for different types of systems. In this thesis we present an interferometric device that allows us to generate and perform tomography on a pure polarization-path two-qubit state. 18 intensity measurements are required for characterizing each state. We test our proposal in an experiment and compare the results with the theoretical predictions.
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Catani, Lorenzo. "Accessible information in a two-qubit system through the quantum steering ellipsoids formalism." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7178/.

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Capire come ottenere l'informazione accessibile, cioè quanta informazione classica si può estrarre da un processo quantistico, è una delle questioni più intricate e affascinanti nell'ambito della teoria dell'informazione quantistica. Nonostante l'importanza della nozione di informazione accessibile non esistono metodi generali per poterla calcolare, esistono soltanto dei limiti, i più famosi dei quali sono il limite superiore di Holevo e il limite inferiore di Josza-Robb-Wootters. La seguente tesi fa riferimento a un processo che coinvolge due parti, Alice e Bob, che condividono due qubits. Si considera il caso in cui Bob effettua misure binarie sul suo qubit e quindi indirizza lo stato del qubit di Alice in due possibili stati. L'obiettivo di Alice è effettuare la misura ottimale nell'ottica di decretare in quale dei due stati si trova il suo qubit. Lo strumento scelto per studiare questo processo va sotto il nome di 'quantum steering ellipsoids formalism'. Esso afferma che lo stato di un sistema di due qubit può essere descritto dai vettori di Bloch di Alice e Bob e da un ellissoide nella sfera di Bloch di Alice generato da tutte le possibili misure di Bob. Tra tutti gli stati descritti da ellissoidi ce ne sono alcuni che manifestano particolari proprietà, per esempio gli stati di massimo volume. Considerando stati di massimo volume e misure binarie si è riuscito a trovare un limite inferiore all'informazione accessibile per un sistema di due qubit migliore del limite inferiore di Josza-Robb-Wootters. Un altro risultato notevole e inaspettato è che l'intuitiva e giustificata relazione 'distanza tra i punti nell'ellissoide - mutua informazione' non vale quando si confrontano coppie di punti ''vicine'' tra loro e lontane dai più distanti.
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Perez, Veitia Andrzej. "Local Entanglement Generation in Two-Qubit Systems." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/476.

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We study the entanglement of two-qubit systems resulting from local interactions with spatially extended bosonic systems. Our results apply to the case where the initial state of the bosonic system is represented by a statistical mixture of states with fixed particle number. In particular, we derive and discuss necessary conditions to generate entanglement in the two-qubit system. We also study the scenario where the joint system is initially in its ground state and the interaction is switched on adiabatically. Using time independent perturbation theory and the adiabatic theorem, we show conditions under which the qubits become entangled as the joint system evolves into the ground state of the interacting theory
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Weichselbaum, Andreas. "Nanoscale Quantum Dynamics and Electrostatic Coupling." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1091115085.

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Dilley, Daniel Jacob. "An Insight on Nonlocal Correlations in Two-Qubit Systems." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2069.

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In this paper, we introduce the motivation for Bell inequalities and give some background on two different types: CHSH and Mermin's inequalities. We present a proof for each and then show that certain quantum states can violate both of these inequalities. We introduce a new result stating that for four given measurement directions of spin, two respectively from Alice and two from Bob, which are able to produce a violation of the Bell inequality for an arbitrary shared quantum state will also violate the Bell inequality for a maximally entangled state. Then we provide another new result that characterizes all of the two-qubit states that violate Mermin's inequality.
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Santos, Marcelo Meireles dos. "Soluções exatas e medidas de emaranhamento em sistemas de spins." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-23032018-210425/.

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Recentemente, uma implementação de um conjunto universal de portas lógicas de um e dois qubits para computação quântica usando estados de spin de pontos quânticos de um único elétron foi proposta. Estes resultados nos motivaram a desenvolver um estudo teórico formal do correspondente modelo de dois spins colocados em um campo magnético externo e acoplados por uma interação mútua de Heisenberg dependente do tempo. Nós então consideramos a assim chamada equação de dois spins, a qual descreve sistemas quânticos de quatro níveis de energia. Uma útil propriedade dessa equação é que o correspondente problema para o caso de campos magnéticos externos paralelos pode ser reduzido ao problema de um único spin em um campo externo efetivo. Isso nos permite gerar uma série de soluções exatas para a equação de dois spins a partir de soluções exatas já conhecidas da equação de um spin. Com base neste fato, nós construímos e apresentamos neste estudo uma lista de novas soluções exatas para a equação de dois spins para diferentes configurações de campos externos e de interação entre as partículas. Utilizando algumas destas soluções obtidas, estudamos a dinâmica da entropia de emaranhamento dos respectivos sistemas considerando diferentes estados de spins inicialmente separáveis.
Recently, an implementation of a universal set of one- and two-qubit logic gates for quantum computing using spin states of single-electron quantum dots was proposed. These results motivated us to develop a formal theoretical study of the corresponding model of two spins placed in an external magnetic field and coupled by a time-dependent mutual interaction of Heisenberg. We then consider the so-called two-spin equation, which describes four-level quantum systems. A useful property of this equation is that the corresponding problem for the case of parallel external magnetic fields can be reduced to the problem of a single spin in an effective external field. This allows us to generate a series of exact solutions for the two-spin equation from the already known exact solutions of the one-spin equation. Based on this fact, we construct and present in this study a list of new exact solutions for the two-spin equation for different configurations of external fields and interaction between particles. Using some of these solutions obtained, we study the dynamics of the entropy of entanglement of the respective systems considering different initially separable spins states.
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KALSON, SHWETA, and ANCHAL SINGH. "A FEW ENTANGLEMENT CRITERION FOR TWO-QUBIT AND TWO-QUDIT SYSTEMS BASED ON REALIGNMENT OPERATION." Thesis, 2022. http://dspace.dtu.ac.in:8080/jspui/handle/repository/19614.

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It is known that realignment crierion is necessary but not a sufficient criterion even for a two-qubit system. We have derived necessary and sufficient condition based on realignment operation for a particular class of two-qubit system and thus solved this problem partially for two-qubit system. We have shown that the lower bound of the trace norm of realigned form of the particular form of the density matrix exists if and only if the two-qubit state is entangled. The derived necessary and sufficient condition detects two-qubit entangled states, which are not detected by the realignment criterion. Further, we have obtained the upper bound of the minimum singular value of the realigned form of the density matrix for the d ⊗ d dimensional separable states. Moreover, we provide the geometrical interpretation of the derived separability criterion for d ⊗ d dimensional system. Moreover, we show that our criterion may also detect bound entangled state. Our criterion is beneficial in the sense that it requires to calculate only minimum singular value of the realigned matrix while on the other hand realignment criterion requires all singular values of the realigned matrix. Thus, our criterion has computational advantage over the realignment criterion.
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Book chapters on the topic "TWO-QUBIT SYSTEM"

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Diósi, Lajos. "Two-State Q-System: Qubit Representations." In A Short Course in Quantum Information Theory, 37–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-16117-9_5.

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Wang, Jinwei. "Bidirectional Controlled Quantum Teleportation of Two-Qubit State via Eight-Qubit Entangled State." In Advances in Natural Computation, Fuzzy Systems and Knowledge Discovery, 500–508. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-20738-9_57.

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Flarend, Alice, and Bob Hilborn. "Multi-Qubit Systems, Entanglement, and Quantum Weirdness." In Quantum Computing: From Alice to Bob, 109–34. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780192857972.003.0009.

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Quantum state entanglement is a crucial ingredient in many quantum algorithms. This chapter introduces the description of multi-qubit quantum systems and then explains what it means to say the state of that system is entangled. If the quantum state of the system is an entangled state, none of the constituents of the system are described by their own individual states. For a two-qubit entangled state, measurements of one of the qubits apparently affect the measurement results of the other even though the two qubits may be far apart. The change in basis states, introduced in Chapter 8, is applied to a two-qubit system, which will be used to illustrate Bell’s theorem. That theorem tells us that the quantum description of the world profoundly violates almost every concept we have about material properties and the measurement of those properties.
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Bhat, Hilal Ahmad, Farooq Ahmad Khanday, and Khurshed Ahmad Shah. "Optimal Circuit Decomposition of Reversible Quantum Gates on IBM Quantum Computers." In Advances in Systems Analysis, Software Engineering, and High Performance Computing, 149–64. IGI Global, 2023. http://dx.doi.org/10.4018/978-1-6684-6697-1.ch008.

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A critical task in utilizing quantum physics in many application fields is circuit design using reversible quantum gates. Using decomposition techniques enables transformation of unitary matrices into fundamental quantum gates. Any 3x3 reversible quantum gate can be decomposed into single-qubit rotation gates and two qubit CNOT gates. In this chapter, quantum implementations of FRSG1, URG, JTF1 and R gates into CNOT gates and single qubit U3 gates with different optimization levels on a platform provided by IBM have been discussed. FRSG1 and JTF1 gates are important in applications like Stochastic computing, fingerprint authentication system, and parity generation circuits. URG gate is better in terms of number of complex functions and can be utilized to design quantum comparator circuits. R gate plays an important role in inverting and duplicating a signal. In FRSG1, URG, JTF1 and R gates, the implementation count of single qubit gates decreases by 56%, 11%, 71%, and 62%, respectively and the count of two qubit gates reduces by 15%, 26%, 41%, and 5% respectively after optimization.
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Kaye, Phillip, Raymond Laflamme, and Michele Mosca. "Superdense Coding and Quantum Teleportation." In An Introduction to Quantum Computing. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198570004.003.0008.

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We are now ready to look at our first protocols for quantum information. In this section, we examine two communication protocols which can be implemented using the tools we have developed in the preceding sections. These protocols are known as superdense coding and quantum teleportation. Both are inherently quantum: there are no classical protocols which behave in the same way. Both involve two parties who wish to perform some communication task between them. In descriptions of such communication protocols (especially in cryptography), it is very common to name the two parties ‘Alice’ and ‘Bob’, for convenience. We will follow this tradition. We will repeatedly refer to communication channels. A quantum communication channel refers to a communication line (e.g. a fiberoptic cable), which can carry qubits between two remote locations. A classical communication channel is one which can carry classical bits (but not qubits).1 The protocols (like many in quantum communication) require that Alice and Bob initially share an entangled pair of qubits in the Bell state The above Bell state is sometimes referred to as an EPR pair. Such a state would have to be created ahead of time, when the qubits are in a lab together and can be made to interact in a way which will give rise to the entanglement between them. After the state is created, Alice and Bob each take one of the two qubits away with them. Alternatively, a third party could create the EPR pair and give one particle to Alice and the other to Bob. If they are careful not to let them interact with the environment, or any other quantum system, Alice and Bob’s joint state will remain entangled. This entanglement becomes a resource which Alice and Bob can use to achieve protocols such as the following. Suppose Alice wishes to send Bob two classical bits of information. Superdense coding is a way of achieving this task over a quantum channel, requiring only that Alice send one qubit to Bob. Alice and Bob must initially share the Bell state Suppose Alice is in possession of the first qubit and Bob the second qubit.
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Rau, Jochen. "Communication." In Quantum Theory, 223–60. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192896308.003.0005.

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This chapter introduces the notions of classical and quantum information and discusses simple protocols for their exchange. It defines the entropy as a quantitative measure of information, and investigates its mathematical properties and operational meaning. It discusses the extent to which classical information can be carried by a quantum system and derives a pertinent upper bound, the Holevo bound. One important application of quantum communication is the secure distribution of cryptographic keys; a pertinent protocol, the BB84 protocol, is discussed in detail. Moreover, the chapter explains two protocols where previously shared entanglement plays a key role, superdense coding and teleportation. These are employed to effectively double the classical information carrying capacity of a qubit, or to transmit a quantum state with classical bits, respectively. It is shown that both protocols are optimal.
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Steel, Duncan G. "Quantum Dynamics: Resonance and a Quantum Flip-Flop." In Introduction to Quantum Nanotechnology, 135–59. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192895073.003.0009.

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This chapter begins the discussion of the time evolution of an active quantum system. From the earlier chapters, time dependent physics has been observed through the presence of the time evolution of the phase of each eigenstate. The Hamiltonian itself is time independent. This represents the same kind of evolution of a classical system like the vibration of a tuning fork when it has been struck or the oscillation of an LC circuit if the capacitor is charged to some voltage and then the switch is closed. In the quantum case, the Hamiltonian has also been time independent. The time evolution evolves according the full-time dependent Schrödinger equation, depending only on a single initial condition of the state vector or wave function and the corresponding time evolution of the phase factor for each eigenstate. However in this chapter, we consider the case of when there is a time dependent Hamiltonian such as a sinewave generator or laser. As in the case of resonant tunneling, we see the importance in dynamics of resonant coupling. With an oscillating potential energy term, we see the presence of Rabi oscillations in the probability amplitude of a two-state system on resonance, which can be viewed as a quantum flip-flop between two states of a quantum bit (qubit).
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Kaye, Phillip, Raymond Laflamme, and Michele Mosca. "Qubits and the Framework of Quantum Mechanics." In An Introduction to Quantum Computing. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198570004.003.0006.

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In this section we introduce the framework of quantum mechanics as it pertains to the types of systems we will consider for quantum computing. Here we also introduce the notion of a quantum bit or ‘qubit’, which is a fundamental concept for quantum computing. At the beginning of the twentieth century, it was believed by most that the laws of Newton and Maxwell were the correct laws of physics. By the 1930s, however, it had become apparent that these classical theories faced serious problems in trying to account for the observed results of certain experiments. As a result, a new mathematical framework for physics called quantum mechanics was formulated, and new theories of physics called quantum physics were developed in this framework. Quantum physics includes the physical theories of quantum electrodynamics and quantum field theory, but we do not need to know these physical theories in order to learn about quantum information. Quantum information is the result of reformulating information theory in this quantum framework. We saw in Section 1.6 an example of a two-state quantum system: a photon that is constrained to follow one of two distinguishable paths. We identified the two distinguishable paths with the 2-dimensional basis vectors and then noted that a general ‘path state’ of the photon can be described by a complex vector with |α0|2 +|α1|2 = 1. This simple example captures the essence of the first postulate, which tells us how physical states are represented in quantum mechanics. Depending on the degree of freedom (i.e. the type of state) of the system being considered, H may be infinite-dimensional. For example, if the state refers to the position of a particle that is free to occupy any point in some region of space, the associated Hilbert space is usually taken to be a continuous (and thus infinite-dimensional) space. It is worth noting that in practice, with finite resources, we cannot distinguish a continuous state space from one with a discrete state space having a sufficiently small minimum spacing between adjacent locations. For describing realistic models of quantum computation, we will typically only be interested in degrees of freedom for which the state is described by a vector in a finite-dimensional (complex) Hilbert space.
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Flarend, Alice, and Bob Hilborn. "Putting a Spin on Spin." In Quantum Computing: From Alice to Bob, 71–77. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780192857972.003.0007.

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This chapter provides a brief introduction to the terminology and basic concepts of quantum spin systems, which are widely used in QIS and QC. The quantum spin of an elementary particle is an example of a qubit and can be visually represented as a spinning top. The vector direction of spin in state space, however, is different from the direction in physical space. Quantum spin-1/2 systems have two orthogonal states: spin-up and spin-down. The distinction between state space angles and physical space angles is emphasized. Because spin is a qubit, the quantum gates from Chapter 6 can be applied to spin-1/2 quantum states with predictable results.
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Barnett, Stephen. "Quantum information processing." In Quantum Information. Oxford University Press, 2009. http://dx.doi.org/10.1093/oso/9780198527626.003.0009.

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We have seen how information can be encoded onto a quantum system by selecting the state in which it is prepared. Retrieving the information is achieved by performing a measurement, and the optimal measurement in any given situation is usually a generalized measurement. In between preparation and measurement, the information resides in the quantum state of the system, which evolves in a manner determined by the Hamiltonian. The associated unitary transformation may usefully be viewed as quantum information processing; if we can engineer an appropriate Hamiltonian then we can use the quantum evolution to assist in performing computational tasks. Our objective in quantum information processing is to implement a desired unitary transformation. Typically this will mean coupling together a number, perhaps a large number, of qubits and thereby generating highly entangled states. It is fortunate, although by no means obvious, that we can realize any desired multiqubit unitary transformation as a product of a small selection of simple transformations and, moreover, that each of these need only act on a single qubit or on a pair of qubits. The situation is reminiscent of digital electronics, in which logic operations are decomposed into actions on a small number of bits. If we can realize and control a very large number of such operations in a single device then we have a computer. Similar control of a large number of qubits will constitute a quantum computer. It is the revolutionary potential of quantum computers, more than any other single factor, that has fuelled the recent explosion of interest in our subject. We shall examine the remarkable properties of quantum computers in the next chapter. In digital electronics, we represent bit values by voltages: the logical value 1 is a high voltage (typically +5 V) and 0 is the ground voltage (0 V). The voltage bits are coupled and manipulated by transistor-based devices, or gates. The simplest gates act on only one bit or combine two bits to generate a single new bit, the value of which is determined by the two input bits. For a single bit, with value 0 or 1, the only possible operations are the identity (which does not require a gate) and the bit flip.
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Conference papers on the topic "TWO-QUBIT SYSTEM"

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Stefanov, A. A., and D. M. Mladenov. "Euler angles parametrization of a two qubit system." In RENEWABLE ENERGY SOURCES AND TECHNOLOGIES. AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5127498.

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Wang, Ye, Stephen Crain, Chao Fang, Bichen Zhang, Pak Hong Leung, Shilin Huang, Qiyao Liang, Kenneth R. Brown, and Jungsang Kim. "High-fidelity Two-qubit Gates Using a MEMS-based Beam Steering System for Individual Qubit Addressing." In Quantum 2.0. Washington, D.C.: OSA, 2020. http://dx.doi.org/10.1364/quantum.2020.qw5b.1.

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Asaoka, Rui, Takeru Utsugi, Yuuki Tokunaga, Rina Kanamoto, and Takao Aoki. "Optimization of a cavity-QED system for fast two-qubit gates." In 2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). IEEE, 2021. http://dx.doi.org/10.1109/cleo/europe-eqec52157.2021.9542055.

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Johansson, J. R., S. Ashhab, A. M. Zagoskin, and F. Nori. "Dynamics of a superconducting qubit coupled to quantum two-level systems in its environment." In Workshop on Entanglement and Quantum Decoherence. Washington, D.C.: Optica Publishing Group, 2008. http://dx.doi.org/10.1364/weqd.2008.qia3.

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We study the decoherence dynamics of a superconducting qubit coupled to a quantum two-level system (TLS) in addition to its weak coupling to a background environment [1]. We identify two weak-coupling regimes, which differ by the relation between qubit and TLS decoherence times, and a strong coupling regime. We find expressions for the qubit decoherence rates in the weak-coupling regimes. For a weakly coupled and strongly dissipative TLS we find that the qubit dynamics is markovian, whereas for a weakly dissipative TLS the qubit dynamics shows non-markovian behavior. In the strong-coupling regime we study the driven qubit dynamics and we analyze the differences from standard Rabi-oscillations due to the coupling to the quantum TLS [2]. In doing so we identify signatures in the qubit dynamics that can be used to characterize the TLS. We also investigate the possibility of using environmental TLSs with long coherence times for quantum information processing [3]. By using the Josephson junction as a bus and the TLSs in the environment as qubits, we demonstrate that initialization, a universal set of quantum gates, and read-out of the TLSs can be implemented, even though the TLSs themselves cannot be directly accessed.
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Chiu, Tai-Yin, and Kuan-Ting Lin. "Optimal control of two-qubit quantum gates in a non-Markovian open system." In 2016 12th IEEE International Conference on Control and Automation (ICCA). IEEE, 2016. http://dx.doi.org/10.1109/icca.2016.7505375.

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ASHHAB, S., J. R. JOHANSSON, and FRANCO NORI. "DECOHERENCE AND RABI OSCILLATIONS IN A QUBIT COUPLED TO A QUANTUM TWO-LEVEL SYSTEM." In Proceedings of the International Symposium. WORLD SCIENTIFIC, 2008. http://dx.doi.org/10.1142/9789812814623_0014.

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Huang, Yuwen, and Pascal O. Vontobel. "Sets of Marginals and Pearson-Correlation-based CHSH Inequalities for a Two-Qubit System." In 2021 IEEE International Symposium on Information Theory (ISIT). IEEE, 2021. http://dx.doi.org/10.1109/isit45174.2021.9518116.

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Deçordi, G. L., and A. Vidiella-Barranco. "Sudden Death of Entanglement in a Two-Qubit System Coupled to a Small Environment." In Conference on Coherence and Quantum Optics. Washington, D.C.: OSA, 2019. http://dx.doi.org/10.1364/cqo.2019.m5a.7.

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Geru, Ion. "Superdense Coding of Information in Quantum Computer in the Paired Bosons Representation." In 11th International Conference on Electronics, Communications and Computing. Technical University of Moldova, 2022. http://dx.doi.org/10.52326/ic-ecco.2021/tap.04.

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An alternative approach to superdense coding of information in quantum computing is proposed on the basis of Schwinger’s two-boson representation of angular momentum. Since the effective spin S = 2n-1 - ½ corresponds to the n-qubit system, this representation can be used in the quantum computing. Operators of the logical elements of the quantum circuit were found, performing superdense coding of information in the paired bosons representation. It is shown that for superdense coding of information, the results obtained in the spinor representation and in the representation of paired bosons coincide. For one-qubit systems, one of the two representations cannot be favored. In the case of n-qubit systems for n >> 1, the representation of paired bosons is probably more convenient for applications, since in this representation the explicit form of the Pauli operators X, Y, and Z does not depend on n.
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Privman, Vladimir, Dmitry Solenov, and Denis Tolkunov. "Onset of Entanglement and Noise Cross-Correlations in Two-Qubit System Interacting with Common Bosonic Bath." In 2006 8th International Conference on Solid-State and Integrated Circuit Technology Proceedings. IEEE, 2006. http://dx.doi.org/10.1109/icsict.2006.306659.

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Reports on the topic "TWO-QUBIT SYSTEM"

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Farhi, Edward, and Hartmut Neven. Classification with Quantum Neural Networks on Near Term Processors. Web of Open Science, December 2020. http://dx.doi.org/10.37686/qrl.v1i2.80.

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We introduce a quantum neural network, QNN, that can represent labeled data, classical or quantum, and be trained by supervised learning. The quantum circuit consists of a sequence of parameter dependent unitary transformations which acts on an input quantum state. For binary classification a single Pauli operator is measured on a designated readout qubit. The measured output is the quantum neural network’s predictor of the binary label of the input state. We show through classical simulation that parameters can be found that allow the QNN to learn to correctly distinguish the two data sets. We then discuss presenting the data as quantum superpositions of computational basis states corresponding to different label values. Here we show through simulation that learning is possible. We consider using our QNN to learn the label of a general quantum state. By example we show that this can be done. Our work is exploratory and relies on the classical simulation of small quantum systems. The QNN proposed here was designed with near-term quantum processors in mind. Therefore it will be possible to run this QNN on a near term gate model quantum computer where its power can be explored beyond what can be explored with simulation.
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