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[Texts and Readings in Physical Sciences] Open Quantum Systems Volume 20 (Dynamics of Nonclassical Evolution) || Open Quantum System at Interface with Quantum Information
摘要： This chapter is devoted to the interface between open system ideas and the burgeoning field of quantum information. Quantum information is, as the name suggests, the broad name given to information tasks that make use of the laws of quantum mechanics. It encompasses within its purview, communication, computation and foundational information theoretical tasks. Information theoretic ideas pervade the whole of physics and make inroads beyond it. As it involves encoding, transmission and decoding of information as bits or qubits, all of which are very sensitive to their ambient environment, they provide a fruitful ground for the application of open system ideas. In fact, this chapter and the next one bear testimony to this.
关键词： quantum information,open quantum systems,quantum computation,quantum error correction,quantum communication
更新于2025-09-23 15:21:01
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Versatile relative entropy bounds for quantum networks
摘要： We provide a versatile upper bound on the number of maximally entangled qubits, or private bits, shared by two parties via a generic adaptive communication protocol over a quantum network when the use of classical communication is not restricted. Although our result follows the idea of Azuma et al (2016 Nat. Commun. 7 13523) of splitting the network into two parts, our approach relaxes their strong restriction, consisting of the use of a single entanglement measure in the quanti?cation of the maximum amount of entanglement generated by the channels. In particular, in our bound the measure can be chosen on a channel-by-channel basis, in order to make it as tight as possible. This enables us to apply the relative entropy of entanglement, which often gives a state-of-the-art upper bound, on every Choi-simulable channel in the network, even when the other channels do not satisfy this property. We also develop tools to compute, or bound, the max-relative entropy of entanglement for channels that are invariant under phase rotations. In particular, we present an analytical formula for the max-relative entropy of entanglement of the qubit amplitude damping channel.
关键词： quantum networks,quantum communication,quantum information
更新于2025-09-23 15:21:01
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Geometrical self-testing of partially entangled two-qubit states
摘要： Quantum nonlocality has recently been intensively studied in connection to device-independent quantum information processing, where the extremal points of the set of quantum correlations play a crucial role through self-testing. In most protocols, the proofs for self-testing rely on the maximal violation of the Bell inequalities, but there is another known proof based on the geometry of state vectors to self-test a maximally entangled state. We present a geometrical proof in the case of partially entangled states. We show that, when a set of correlators in the simplest Bell scenario satisfies a condition, the geometry of the state vectors is uniquely determined. The realization becomes self-testable when another unitary observable exists on the geometry. Applying this proven fact, we propose self-testing protocols by intentionally adding one more measurement. This geometrical scheme for self-testing is superior in that, by using this as a building block and repeatedly adding measurements, a realization with an arbitrary number of measurements can be self-tested. Besides the application, we also attempt to describe nonlocal correlations by guessing probabilities of distant measurement outcomes. In this description, the quantum set is also convex, and a large class of extremal points is identified by the uniqueness of the geometry.
关键词： device-independent quantum information processing,Bell inequality,quantum nonlocality,self-testing
更新于2025-09-23 15:21:01
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Unprecedented charge state control in graphene quantum dots
摘要： High-quality double quantum dots in bilayer graphene are realized with controlled charge down to one electron. These devices provide a promising basis for spin-based qubits with long spin lifetimes.
关键词： Quantum dots,graphene,spintronics,quantum information
更新于2025-09-23 15:21:01
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Rabi Oscillation Study of Strong Coupling in a Plasmonic Nanocavity
摘要： Strong interaction between emitters and plasmonic nanocavity has various applications in quantum fields at room temperature. As Rabi oscillation gives the direct proof to the energy exchange in strong coupling, it is more intuitive and necessary to analyze the interaction in time domain. In this paper, we give the Rabi oscillation in a high-dissipation plasmonic nanocavity by using full-quantum method and draw a new strong coupling criterion about mode volume which provides a significant guidance in plasmonic nanocavitys nanofabrication. Moreover, we reveal the relation between Rabi oscillation and Rabi splitting, which is beneficial for exploring emitter-plasmon hybrid systems time-domain property through frequency-domain response. An emitter-hexagon hybrid system with ultrasmall mode volume is designed to verify our theory. The numerical simulation shows good agreements with our theoretical results. Our work has applications in quantum information and quantum computing in the future.
关键词： plasmonic nanocavity,quantum information,Rabi oscillation,quantum computing,strong coupling
更新于2025-09-23 15:21:01
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Toward Valleya??Coupled Spin Qubits
摘要： The bid for scalable physical qubits has attracted many possible candidate platforms. In particular, spin-based qubits in solid-state form factors are attractive as they could potentially benefit from processes similar to those used for conventional semiconductor processing. However, material control is a significant challenge for solid-state spin qubits as residual spins from substrate, dielectric, electrodes, or contaminants from processing contribute to spin decoherence. In the recent decade, valleytronics has seen a revival due to the discovery of valley-coupled spins in monolayer transition metal dichalcogenides. Such valley-coupled spins are protected by inversion asymmetry and time reversal symmetry and are promising candidates for robust qubits. In this report, the progress toward building such qubits is presented. Following an introduction to the key attractions in fabricating such qubits, an up-to-date brief is provided for the status of each key step, highlighting advancements made and/or outstanding work to be done. This report concludes with a perspective on future development highlighting major remaining milestones toward scalable spin-valley qubits.
关键词： valleytronics,qubits,quantum information,transition metal dichalcogenides,quantum dots
更新于2025-09-23 15:21:01
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Sufficient condition for a quantum state to be genuinely quantum non-Gaussian
摘要： We show that the expectation value of the operator position and momentum operators x? and p? with a positive parameter c can serve as a tool to identify quantum non-Gaussian states, that is states that cannot be represented as a mixture of Gaussian states. Our condition can be readily tested employing a highly efficient homodyne detection which unlike quantum-state tomography requires the measurements of only two orthogonal quadratures. We demonstrate that our method is even able to detect quantum non-Gaussian states with positive–definite Wigner functions. This situation cannot be addressed in terms of the negativity of the phase-space distribution. Moreover, we demonstrate that our condition can characterize quantum non-Gaussianity for the class of superposition states consisting of a vacuum and integer multiples of four photons under more than 50 % signal attenuation.
关键词： Wigner functions,quantum information,continuous variables,non-Gaussian states,quadrature measurements,Gaussian state
更新于2025-09-23 15:21:01
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Alternative method for deriving nonlocal multipartite product states
摘要： We can only perform finite rounds of measurements in protocols with local operations and classical communication (LOCC). In this paper, we propose a set of product states that require infinite rounds of measurements in order to distinguish this given set of states perfectly by LOCC. Therefore, we can conclude that these sets of states are locally indistinguishable. More accurately, given any multipartite LOCC indistinguishable set where every local system cannot start with a nontrivial measurement, then after appending these states with arbitrarily choosing two nonorthogonal states, we obtain another LOCC indistinguishable set. It can be seen that some parties can perform some nontrivial measurements. Hence, these sets are quite different from those constructed before. This result broadens the knowledge of nonlocality without entanglement to a certain extent.
关键词： entanglement,LOCC,product states,quantum information,nonlocality
更新于2025-09-23 15:21:01
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The Integration of Photonic Crystal Waveguides with Atom Arrays in Optical Tweezers
摘要： Integrating nanophotonics and cold atoms has drawn increasing interest in recent years due to diverse applications in quantum information science and the exploration of quantum many-body physics. For example, dispersion-engineered photonic crystal waveguides (PCWs) permit not only stable trapping and probing of ultracold neutral atoms via interactions with guided-mode light, but also the possibility to explore the physics of strong, photon-mediated interactions between atoms, as well as atom-mediated interactions between photons. While diverse theoretical opportunities involving atoms and photons in 1D and 2D nanophotonic lattices have been analyzed, a grand challenge remains the experimental integration of PCWs with ultracold atoms. Here, an advanced apparatus that overcomes several significant barriers to current experimental progress is described, with the goal of achieving strong quantum interactions of light and matter by way of single-atom tweezer arrays strongly coupled to photons in 1D and 2D PCWs. Principal technical advances relate to efficient free-space coupling of light to and from guided modes of PCWs, silicate bonding of silicon chips within small glass vacuum cells, and deterministic, mechanical delivery of single-atom tweezer arrays to the near fields of photonic crystal waveguides.
关键词： atoms and nanophotonics,quantum simulation,quantum dielectrics,quantum information science
更新于2025-09-23 15:19:57
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Adaptive tomography of qubits: purity versus statistical fluctuations
摘要： The success of quantum information processing applications relies on accurate and efficient characterization of quantum states, especially nearly-pure states. In this work, we investigate a procedure for adaptive qubit state tomography which achieves O(1/N) scaling in accuracy for large N. We analyze the performance of the adaptive protocol on the characterization of pure, mixed and nearly-pure states, and clarify the interplay between the purity of the state and the statistical fluctuations of the measurement results. Our results highlight the subtle difference between the characterization of nearly-pure states and those of pure or highly mixed states.
关键词： quantum information processing,quantum measurement,quantum tomography
更新于2025-09-23 15:19:57