Showing 1–44 of 44 results for author: Yu, B

Reinventing the Single-pixel Imaging Paradigm via Quantum-Operator-Based Signal Processing

Authors: Bu-Ran Yu, Yi-Zhu Zhang, Kan-Xu Jia, Qian-Qian Bao, Shao-Ying Meng, Xi-Hao Chen

Abstract: A fundamental bottleneck across modern computational imaging and high-dimensional sensing is the conventional decoupled acquisition-reconstruction hierarchy, which subjects high-dimensional spatial sensing to the classical shot-noise limit and intense computational overhead. As a prominent manifestation of this limitation, single-pixel imaging (SPI) suffers severely from this paradigm. We reinvent… ▽ More A fundamental bottleneck across modern computational imaging and high-dimensional sensing is the conventional decoupled acquisition-reconstruction hierarchy, which subjects high-dimensional spatial sensing to the classical shot-noise limit and intense computational overhead. As a prominent manifestation of this limitation, single-pixel imaging (SPI) suffers severely from this paradigm. We reinvent this paradigm by introducing a quantum-operator-based SPI theoretical framework driven by coherent signal processing. Within this architecture, the spatial inverse problem is analytically mapped into the eigenvalue spectrum of a quantum operator via tailored light-matter interactions. By analytically synthesizing non-linear reconstruction operators via ultra-shallow quantum architectures, we theoretically demonstrate an exponential decay of spatial approximation errors, completely bypassing traditional linear solvers. This operator-space embedding not only shields reconstruction from noise via a strategic error-saturation zone but also bridges the gap from classical shot-noise scaling $\mathcal{O}(1/\sqrt{N_{\text{ph}}})$ to the ultimate Heisenberg limit $\mathcal{O}(1/N_{\text{ph}})$. Crucially, while formulated within SPI, this coherent operator paradigm fundamentally extends to general photon-starved, high-dimensional imaging modalities. This work establishes a universal theoretical blueprint for next-generation quantum-enhanced sensing, shifting the paradigm from iterative optimization to coherent operator-space evolution. △ Less

Submitted 22 August, 2026; originally announced August 2026.

Entanglement spectrum ordering and flavor polarization in the two-flavor Schwinger model at vacuum angle $θ= π$

Authors: Boliang Yu, Ruixin Zhou, Meisen Gao

Abstract: Entanglement spectra in gauge theories can encode both symmetry breaking and the organization of gauge sectors. In the two-flavor Schwinger model at vacuum angle $θ=π$, we find that the joint Schmidt distribution $p_{Q_A,F_A}$, labeled by the subsystem gauge charge $Q_A$ and flavor imbalance $F_A$, reveals a cut-dependent gauge-sector hierarchy and a mass-induced flavor asymmetry: changing the sta… ▽ More Entanglement spectra in gauge theories can encode both symmetry breaking and the organization of gauge sectors. In the two-flavor Schwinger model at vacuum angle $θ=π$, we find that the joint Schmidt distribution $p_{Q_A,F_A}$, labeled by the subsystem gauge charge $Q_A$ and flavor imbalance $F_A$, reveals a cut-dependent gauge-sector hierarchy and a mass-induced flavor asymmetry: changing the staggered cut reorganizes the gauge-charge distribution $p_{Q_A}$, while mass imbalance breaks the $F_A\leftrightarrow-F_A$ symmetry of the conditional flavor distribution $p_{F_A|Q_A}$. Defining the combined weight $W_F^{(q)}=p_{q,+1}+p_{q,-1}$ and conditional polarization $\mathcal P_F^{(q)}=(p_{q,+1}-p_{q,-1})/W_F^{(q)}$, we find that changing the cut reverses the weight hierarchy, $W_F^{(-1)}>W_F^{(+1)}$ at unit-cell boundaries but $W_F^{(+1)}>W_F^{(-1)}$ at intra-cell cuts, while mass imbalance drives $\mathcal P_F^{(q)}$ away from zero with a $q$-dependent cut response. Symmetry resolution therefore separates gauge-sector ordering, sector weight, and flavor polarization that are mixed in the globally ordered entanglement spectrum. △ Less

Submitted 16 August, 2026; v1 submitted 14 August, 2026; originally announced August 2026.

Comments: 21 pages, 6 figures. Submitted to $\textit{Chinese Physics C}$

Observable dependence and rate identifiability in false-vacuum decay of the quantum Ising chain

Authors: Boliang Yu, Ruixin Zhou, Hang Su

Abstract: Extracting a thermodynamic nucleation rate from finite-time quantum dynamics requires separating observable decay from estimator and finite-size validity. We develop a multilevel identification framework for real-time tensor-network simulations of false-vacuum decay in the one-dimensional quantum Ising chain. Across twelve parameter points, the same coherent two-kink amplitudes semi-quantitatively… ▽ More Extracting a thermodynamic nucleation rate from finite-time quantum dynamics requires separating observable decay from estimator and finite-size validity. We develop a multilevel identification framework for real-time tensor-network simulations of false-vacuum decay in the one-dimensional quantum Ising chain. Across twelve parameter points, the same coherent two-kink amplitudes semi-quantitatively predict both infinite-chain survival and magnetization dynamics: the survival coefficient has a median lattice-to-theory ratio of 0.896, while the magnetization-area slope ratios span 0.767--0.931. By contrast, the microscopic nearest-neighbour bond response is coherence dominated: vacuum--pair coherence contributes 60.0--81.5% across seven points with matched bond-dimension control, while substantial late-window slope discrepancies remain that cannot be removed by a scalar normalization. The analysis establishes finite-time survival and magnetization benchmarks and identifies the additional finite-size and branch-validation requirements for a bulk thermodynamic rate interpretation. Within the two-kink model and under the adopted common normalization, the lattice-resolved WKB action gives a median fixed-prefactor rate discrepancy of 4.13% from the coherent-bubble spectral calculation. These results distinguish finite-time lattice--theory consistency from the additional observable and finite-size evidence required to identify a thermodynamic nucleation rate. △ Less

Submitted 24 August, 2026; v1 submitted 11 August, 2026; originally announced August 2026.

Comments: 19 pages, 4 figures. v2: Main text condensed with details moved to supplementary material. v3: Corrected title. Submitted to $\textit{Journal of Physics: Condensed Matter}$

Engineered Randomness for Ubiquitous Quantum-Enhanced Metrology in Exponential-Dimensional Manifolds

Authors: Yaoming Chu, Baiyi Yu, Hartmut Häffner, Markus Heyl, Nathan Goldman, Jianming Cai

Abstract: The exponential growth of many-body Hilbert space presents a fundamental barrier to quantum technology, obscuring the search for physically significant states within an astronomically vast landscape. Consequently, resources for quantum-enhanced metrology have been largely confined to the symmetric subspace whose dimensionality scales only polynomially with the particle number-leaving the vast majo… ▽ More The exponential growth of many-body Hilbert space presents a fundamental barrier to quantum technology, obscuring the search for physically significant states within an astronomically vast landscape. Consequently, resources for quantum-enhanced metrology have been largely confined to the symmetric subspace whose dimensionality scales only polynomially with the particle number-leaving the vast majority of the Hilbert space largely unexplored and poorly understood. Here we challenge this paradigm by demonstrating that metrological advantage can arise as a ubiquitous feature across exponential-dimensional manifolds. By tailoring the first-moment structure of random unitaries, we uncover dense manifolds of engineered random states (ERSs) where Heisenberg-limited scaling emerges as a statistically generic property. This ubiquity endows these resource states with inherent resilience against parameter disorder. We experimentally validate this framework on a trapped-ion processor, achieving a metrological enhancement of $6.98 \pm 0.38$ dB beyond the standard quantum limit. Potential applications extend to diverse platforms, ranging from superconducting circuits and waveguide QED to solid-state spins and polar molecules. Our results establish a powerful paradigm where quantum-enhanced precision can be harvested from the exponential vastness of the Hilbert space. △ Less

Submitted 29 May, 2026; originally announced May 2026.

Comments: 53 pages

Transient dynamics of parametric driving for single-electron image current detection in a Paul trap

Authors: Baiyi Yu, Andris Huang, Isabel Sacksteder, Hartmut Haeffner

Abstract: Nondestructive detection of single-electron motion is crucial for quantum information processing with electrons trapped in Paul traps. The standard approach in Penning traps is to detect the image current induced on the trap electrodes by the electron's oscillatory motion. However, applying this approach in Paul traps for single electrons is currently hindered by motional frequency fluctuations ar… ▽ More Nondestructive detection of single-electron motion is crucial for quantum information processing with electrons trapped in Paul traps. The standard approach in Penning traps is to detect the image current induced on the trap electrodes by the electron's oscillatory motion. However, applying this approach in Paul traps for single electrons is currently hindered by motional frequency fluctuations arising from trap anharmonicities and instabilities in the rf trapping field. In this work, we propose a robust detection scheme exploiting the transient dynamics of parametric driving to overcome these limitations. Distinct from traditional steady-state approaches, our method focuses on the transient regime to break the temporal constraints imposed by steady-state assumptions, thereby enabling fast readout. We show that a controlled ramp of the parametric drive effectively locks the frequency of the electron motion in the transient regime, rendering the signal highly resilient to realistic experimental noise and inherent micromotion. This work paves the way for the experimental realization of nondestructive detection of single-electron motion in Paul traps. △ Less

Submitted 14 May, 2026; originally announced May 2026.

Comments: 7 pages, 5 figures

Nonlocal advantage of quantum imaginarity in Schwarzchild spacetime

Authors: Bing Yu, Xiao-Yong Yang, Xiaoli Hu, Zhi-Xiang Jin, Xiaofen Huang

Abstract: Black hole spacetimes provide a natural setting for quantum systems in curved spacetime, where effects such as Hawking radiation arise from event horizons. In this work, we investigate the impact of the Hawking effect on quantum imaginarity in Schwarzschild spacetime, focusing on nonlocal advantage of quantum imaginarity (NAQI) and assisted imaginarity distillation. For NAQI, it is significantly a… ▽ More Black hole spacetimes provide a natural setting for quantum systems in curved spacetime, where effects such as Hawking radiation arise from event horizons. In this work, we investigate the impact of the Hawking effect on quantum imaginarity in Schwarzschild spacetime, focusing on nonlocal advantage of quantum imaginarity (NAQI) and assisted imaginarity distillation. For NAQI, it is significantly affected by Hawking radiation, exhibiting a pronounced difference between physically accessible and inaccessible regions. It is suppressed in the physically accessible region with increasing Hawking temperature and may vanish, while remaining absent in the physically inaccessible region across the parameter regime. For assisted imaginarity distillation, the Hawking effect modifies the assisted fidelity in a state-dependent manner. In the physically accessible region, the fidelity generally decreases with increasing temperature, indicating reduced distillation capability, whereas the physically inaccessible region exhibits the opposite monotonic trend, indicating enhanced distillation capability. These results highlight distinct operational behaviors of physically accessible and inaccessible regions under relativistic effects, providing insight into quantum imaginarity in curved spacetime. △ Less

Submitted 14 April, 2026; v1 submitted 4 April, 2026; originally announced April 2026.

Comments: 8 pages, 24 figures

Characterization-free classification and identification of the environment between two quantum players

Authors: Masahito Hayashi, Longyang Cao, Baichu Yu, Yuan-Yuan Zhao

Abstract: Classifying the causal structure of quantum channels is essential for verifying quantum networks and certifying quantum resources. We introduce a characterization-free protocol enabling two isolated players, Alice and Bob, to classify and identify the definite-order strategy adopted by an unknown environment mediating their channels. Without assuming knowledge of their devices or the environment,… ▽ More Classifying the causal structure of quantum channels is essential for verifying quantum networks and certifying quantum resources. We introduce a characterization-free protocol enabling two isolated players, Alice and Bob, to classify and identify the definite-order strategy adopted by an unknown environment mediating their channels. Without assuming knowledge of their devices or the environment, the players infer the causal order solely from input-output statistics by testing Markovian conditions that we prove are necessary and sufficient for each strategy class. Remarkably, we prove that even with a minimal random channel consisting of two-outcome POVMs and two-state preparations, the protocol retains full performance with probability one. We experimentally demonstrate the protocol on an optical platform, reliably distinguishing between several strategies. Our results provide a strong and robust tool for causal inference in quantum networks. △ Less

Submitted 24 February, 2026; originally announced February 2026.

Comments: 17 pages, 4 figures

Reusability of Quantum Catalysts

Authors: Haitao Ma, Yantong Li, Yingchun Kang, Bing Yu, Junjing Xing, Zhaobing Fan, Yunlong Xiao

Abstract: Quantum catalysts enable transformations that otherwise would be forbidden, offering a pathway to surpass conventional limits in quantum information processing. Among them, embezzling catalysts stand out for achieving near-perfect performance while tolerating only minimal disturbance, bridging the gap between ideal and practical catalysis. Yet, this superior capability comes at a cost: Each use sl… ▽ More Quantum catalysts enable transformations that otherwise would be forbidden, offering a pathway to surpass conventional limits in quantum information processing. Among them, embezzling catalysts stand out for achieving near-perfect performance while tolerating only minimal disturbance, bridging the gap between ideal and practical catalysis. Yet, this superior capability comes at a cost: Each use slightly degrades the catalyst, leading to an inevitable accumulation of imperfection. This gradual decay defines their most distinctive property -- reusability -- which, despite its fundamental importance, remains largely unexplored. Here, we establish a quantitative framework to characterize the operational lifetime of embezzling catalysts, focusing on their role in entanglement distillation and extending the analysis to quantum teleportation. We show that the catalytic advantage inevitably diminishes with repeated use, deriving bounds on the maximum effective reuse rounds for a desired performance gain. Our results uncover the finite reusability of catalysts in quantum processes and point toward sustainable strategies for quantum communication. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 17 pages, 8 captioned figures

Probing New Forces with Nuclear Clocks

Authors: Cédric Delaunay, Seung J. Lee, Roee Ozeri, Gilad Perez, Wolfram Ratzinger, Bingrong Yu

Abstract: Clocks based on nuclear isomer transitions promise exceptional stability and precision. The low transition energy of the thorium-229 isomer makes it an ideal candidate, as it has been excited by a vacuum-ultraviolet laser and is highly sensitive to subtle interactions. This enables the development of powerful tools for probing new forces, which we call {\it quintessometers}. In this work, we demon… ▽ More Clocks based on nuclear isomer transitions promise exceptional stability and precision. The low transition energy of the thorium-229 isomer makes it an ideal candidate, as it has been excited by a vacuum-ultraviolet laser and is highly sensitive to subtle interactions. This enables the development of powerful tools for probing new forces, which we call {\it quintessometers}. In this work, we demonstrate the potential of nuclear clocks, particularly solid-state variants, to surpass existing limits on scalar field couplings, exceeding the sensitivity of current fifth-force searches at submicron distances and significantly improving equivalence-principle tests at kilometer scales and beyond. Additionally, we highlight the capability of transportable nuclear clocks to detect scalar interactions at distances beyond $10\,$km, complementing space-based missions. △ Less

Submitted 22 October, 2025; v1 submitted 4 March, 2025; originally announced March 2025.

Comments: 9+1 pages, 3 figures; v2: minor changes, references updated, matches journal version

Journal ref: Phys.Rev.D 112 (2025) 9, 095030

Basis-independent Coherence and its Applications

Authors: Zhi-Xiang Jin, Yuan-Hong Tao, Bing Yu, Shao-Ming Fei

Abstract: In the quantitative theory of quantum coherence, the amount of coherence for given states can be meaningfully discussed only when referring to a preferred basis. One of the objections to this quantification is that the amount of coherence is an intrinsically basis-dependent quantity. This limitation can, however, be lifted when considering a set of quantum states invariant under arbitrary unitary… ▽ More In the quantitative theory of quantum coherence, the amount of coherence for given states can be meaningfully discussed only when referring to a preferred basis. One of the objections to this quantification is that the amount of coherence is an intrinsically basis-dependent quantity. This limitation can, however, be lifted when considering a set of quantum states invariant under arbitrary unitary transformations. Thus, we analyze a basis-independent definition of quantum coherence, and the incoherent state is taken as the maximally mixed state. We describe the relationship between the basis-independent and the basis-dependent approaches and give several applications to show the advantages of the former method. The relations among basis-independent coherence, quantum entanglement, and quantum discord are discussed by using the relative entropy within a multipartite system. △ Less

Submitted 10 December, 2024; originally announced December 2024.

Experimental evidence for dipole-phonon quantum logic in a trapped calcium monoxide and calcium ion chain

Authors: Lu Qi, Evan C. Reed, Boyan Yu, Kenneth R. Brown

Abstract: Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. In this work, we demonstrate an experimental implementation of DPQL with a trapped calcium monoxide and calcium ion chain at room temperature. We present evidence for one DPQL signal in two hours of data collection. The signal rises clearly abov… ▽ More Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. In this work, we demonstrate an experimental implementation of DPQL with a trapped calcium monoxide and calcium ion chain at room temperature. We present evidence for one DPQL signal in two hours of data collection. The signal rises clearly above the characterized noise level and has a lower bound on the statistical significance of 4.1$σ$. The rate of observation is limited by the low thermal population in the molecular ground rotational state. △ Less

Submitted 11 November, 2024; originally announced November 2024.

Comments: 11 pages, 10 figures

Strong coherent ion-electron coupling using a wire data bus

Authors: Baiyi Yu, Ralf Betzholz, Jianming Cai

Abstract: Ion-ion coupling over long distances represents a highly useful resource for quantum technologies, for example, to sympathetically cool or interconnect qubits in ion-based quantum-computing architectures. In this respect, the recently demonstrated wire-mediated ion-ion coupling stands due to the simplification of its trap layout and its prospects for deterministic entanglement. However, the streng… ▽ More Ion-ion coupling over long distances represents a highly useful resource for quantum technologies, for example, to sympathetically cool or interconnect qubits in ion-based quantum-computing architectures. In this respect, the recently demonstrated wire-mediated ion-ion coupling stands due to the simplification of its trap layout and its prospects for deterministic entanglement. However, the strength of such coherent ion-wire-ion coupling is typically weak, hindering its practical utilization. Here, we propose a wire-mediated scheme for coherent ion-electron coupling. The scheme not only enables the sympathetic cooling of electrons via advanced ion-cooling techniques, but also allows to promote the effective ion-ion coupling strength by orders of magnitudes via electron mediation. Our work thus paves a way toward quantum information processing in ion-electron hybrid quantum systems. △ Less

Submitted 29 July, 2024; originally announced July 2024.

Comments: 14 pages, 6 figures

Journal ref: Phys. Rev. Appl. 22, 024032 (2024)

Genuinely nonlocal sets with smallest cardinality

Authors: Zong-Xing Xiong, Mao-Sheng Li, Bing Yu, Zhu-Jun Zheng, Lvzhou Li

Abstract: Recently, there is growing interest in the study of genuine nonlocality, which serves to explore the local accessability of global information encoded in orthogonal multipartite quantum states under scenarios where not all subsystems are joined together. For such form of nonlocality, a probably most fundamental question is upon what states it is prone to be manifested. To tackle this, we present i… ▽ More Recently, there is growing interest in the study of genuine nonlocality, which serves to explore the local accessability of global information encoded in orthogonal multipartite quantum states under scenarios where not all subsystems are joined together. For such form of nonlocality, a probably most fundamental question is upon what states it is prone to be manifested. To tackle this, we present in this work genuinely nonlocal sets with the smallest possible cardinality. We first show the existence of genuinely nonlocal sets of three pure states in arbitrary N-partite system. As a byproduct, this also gives new examples of strongly nonlocal sets with dramatically smaller cardinality than ever for all possible systems, settling some related questions effortlessly. Then, for mixed hypothetical states, we show that genuinely nonlocal sets of two even exist, regardless of the number of copies available. In particular, it turns out for both our constructions that certain genuinely entangled states necessarily exist, nontrivially indicating their potential of raising difficulty in locally accessing multipartite quantum information. △ Less

Submitted 12 April, 2026; v1 submitted 16 March, 2024; originally announced March 2024.

Two infinite families of facets of the holographic entropy cone

Authors: Bartlomiej Czech, Yu Liu, Bo Yu

Abstract: We verify that the recently proven infinite families of holographic entropy inequalities are maximally tight, i.e. they are facets of the holographic entropy cone. The proof is technical but it offers some heuristic insight. On star graphs, both families of inequalities quantify how concentrated / spread information is with respect to a dihedral symmetry acting on subsystems. In addition, toric in… ▽ More We verify that the recently proven infinite families of holographic entropy inequalities are maximally tight, i.e. they are facets of the holographic entropy cone. The proof is technical but it offers some heuristic insight. On star graphs, both families of inequalities quantify how concentrated / spread information is with respect to a dihedral symmetry acting on subsystems. In addition, toric inequalities viewed in the K-basis show an interesting interplay between four-party and six-party perfect tensors. △ Less

Submitted 23 August, 2024; v1 submitted 23 January, 2024; originally announced January 2024.

Comments: 18 pages plus appendices, 8 figures, 18 lemmas. v4: one minor but crucial typo fixed

Journal ref: SciPost Phys. 17, 084 (2024)

Measurement-Device-Independent Detection of Beyond-Quantum State

Authors: Baichu Yu, Masahito Hayashi

Abstract: In quantum theory, a quantum state on a composite system of two parties realizes a non-negative probability with any measurement element with a tensor product form. However, there also exist non-quantum states which satisfy the above condition. Such states are called beyond-quantum states, and cannot be detected by standard Bell tests. To distinguish a beyond-quantum state from quantum states, we… ▽ More In quantum theory, a quantum state on a composite system of two parties realizes a non-negative probability with any measurement element with a tensor product form. However, there also exist non-quantum states which satisfy the above condition. Such states are called beyond-quantum states, and cannot be detected by standard Bell tests. To distinguish a beyond-quantum state from quantum states, we propose a measurement-device-independent (MDI) test for beyond-quantum state detection, which is composed of quantum input states on respective parties and quantum measurements across the input system and the target system on respective parties. The performance of our protocol is independent of the forms of the tested states and the measurement operators, which provides an advantage in practical scenarios. We also discuss the importance of tomographic completeness of the input sets to the detection. △ Less

Submitted 31 December, 2023; v1 submitted 11 December, 2023; originally announced December 2023.

Comments: 10 pages, 1 figures

Enhanced quantum channel uncertainty relations by skew information

Authors: Xiaoli Hu, Naihong Hu, Bing Yu, Naihuan Jing

Abstract: By revisiting the mathematical foundation of the uncertainty relation, skew information-based uncertainty sequences are developed for any two quantum channels. A reinforced version of the Cauchy-Schwarz inequality is adopted to improve the uncertainty relation, and a sampling technique of observables' coordinates is used to offset randomness in the inequality. It is shown that the lower bounds of… ▽ More By revisiting the mathematical foundation of the uncertainty relation, skew information-based uncertainty sequences are developed for any two quantum channels. A reinforced version of the Cauchy-Schwarz inequality is adopted to improve the uncertainty relation, and a sampling technique of observables' coordinates is used to offset randomness in the inequality. It is shown that the lower bounds of the uncertainty relations are tighter than some previous studies. △ Less

Submitted 9 October, 2023; originally announced October 2023.

Journal ref: Quantum Inf. Process. 22 (2023), 365 (16pp)

Polygamy relation of quantum correlations with equality

Authors: Zhi-Xiang Jin, Bing Yu, Xue-Na Zhu, Shao-Ming Fei, Cong-Feng Qiao

Abstract: We provide a generalized definition of polygamy relations for any quantum correlation measures. Instead of the usual polygamy inequality, a polygamy relation with equality is given by introducing the polygamy weight. From the polygamy relation with equality, we present polygamy inequalities satisfied by the $β$th $(β>0)$ power of the quantum correlation measures. Taking concurrence of assistance a… ▽ More We provide a generalized definition of polygamy relations for any quantum correlation measures. Instead of the usual polygamy inequality, a polygamy relation with equality is given by introducing the polygamy weight. From the polygamy relation with equality, we present polygamy inequalities satisfied by the $β$th $(β>0)$ power of the quantum correlation measures. Taking concurrence of assistance as an example, we further illustrate the significance and advantages of these relations. We also obtain a polygamy relation with equality by considering the one-to-group entanglements for any quantum entanglement measures that do not satisfy the polygamy relations. We demonstrate that such relations for tripartite states can be generalized to multipartite systems. △ Less

Submitted 23 September, 2023; originally announced September 2023.

Journal ref: Advanced quantum technologies 2300186 (2023)

Neural Network Approach to the Simulation of Entangled States with One Bit of Communication

Authors: Peter Sidajaya, Aloysius Dewen Lim, Baichu Yu, Valerio Scarani

Abstract: Bell's theorem states that Local Hidden Variables (LHVs) cannot fully explain the statistics of measurements on some entangled quantum states. It is natural to ask how much supplementary classical communication would be needed to simulate them. We study two long-standing open questions in this field with neural network simulations and other tools. First, we present evidence that all projective mea… ▽ More Bell's theorem states that Local Hidden Variables (LHVs) cannot fully explain the statistics of measurements on some entangled quantum states. It is natural to ask how much supplementary classical communication would be needed to simulate them. We study two long-standing open questions in this field with neural network simulations and other tools. First, we present evidence that all projective measurements on partially entangled pure two-qubit states require only one bit of communication. We quantify the statistical distance between the exact quantum behaviour and the product of the trained network, or of a semianalytical model inspired by it. Second, while it is known on general grounds (and obvious) that one bit of communication cannot eventually reproduce all bipartite quantum correlation, explicit examples have proved evasive. Our search failed to find one for several bipartite Bell scenarios with up to 5 inputs and 4 outputs, highlighting the power of one bit of communication in reproducing quantum correlations. △ Less

Submitted 29 September, 2023; v1 submitted 31 May, 2023; originally announced May 2023.

Comments: 13 pages, 7 figures, 4 tables. v5: published version; v4: fixed typos and errors in Sec. III C; v3: added a paragraph of discussion at the end of Sec. III and a reference; v2: added references and fixed typos

Journal ref: Quantum 7, 1150 (2023)

Engineering artificial atomic systems of giant electric dipole moment

Authors: Baiyi Yu, Yaoming Chu, Ralf Betzholz, Shaoliang Zhang, Jianming Cai

Abstract: The electric dipole moment (EDM) plays a crucial role in determining the interaction strength of an atom with electric fields, making it paramount to quantum technologies based on coherent atomic control. We propose a scheme for engineering the potential in a Paul trap to realize a two-level quantum system with a giant EDM formed by the motional states of a trapped electron. We show that, under re… ▽ More The electric dipole moment (EDM) plays a crucial role in determining the interaction strength of an atom with electric fields, making it paramount to quantum technologies based on coherent atomic control. We propose a scheme for engineering the potential in a Paul trap to realize a two-level quantum system with a giant EDM formed by the motional states of a trapped electron. We show that, under realistic experimental conditions, the EDM can significantly exceed the ones attainable with Rydberg atoms. Furthermore, we show that such artificial atomic dipoles can be efficiently initialized, readout, and coherently controlled, thereby providing a potential platform for quantum technologies such as ultrahigh-sensitivity electric-field sensing. △ Less

Submitted 21 April, 2023; originally announced April 2023.

Comments: 7 pages, 4 5 figures + 26 pages Supplemental Material. Comments are welcome

Journal ref: Phys. Rev. Lett. 132, 073202 (2024)

Detection of Beyond-Quantum Non-locality based on Standard Local Quantum Observables

Authors: Hayato Arai, Baichu Yu, Masahito Hayashi

Abstract: Device independent detections of quantum non-locality like Bell-CHSH inequality are important methods to detect quantum non-locality because the whole protocol can be implemented by uncertified local observables. However, this detection is not sufficient for the justification of standard quantum theory, because there are theoretically many types of beyond-quantum non-local states in General Probab… ▽ More Device independent detections of quantum non-locality like Bell-CHSH inequality are important methods to detect quantum non-locality because the whole protocol can be implemented by uncertified local observables. However, this detection is not sufficient for the justification of standard quantum theory, because there are theoretically many types of beyond-quantum non-local states in General Probabilistic Theories. One important class is Entanglement Structures (ESs), which contain beyond-quantum non-local states even though their local systems are completely equivalent to standard quantum systems. This paper shows that any device independent detection cannot distinguish beyond-quantum non-local states from standard quantum states. To overcome this problem, this paper gives a device dependent detection based on local observables to distinguish any beyond-quantum non-local state from all standard quantum states. Especially, we give a way to detect any beyond-quantum non-local state in two-qubit ESs by observing only spin observables on local systems. △ Less

Submitted 15 May, 2023; v1 submitted 10 January, 2023; originally announced January 2023.

Comments: 8 pages, 2 figure

Information causality beyond the random access code model

Authors: Baichu Yu, Valerio Scarani

Abstract: Information causality (IC) was one of the first principles that have been invoked to bound the set of quantum correlations. For some families of correlations, this principle recovers exactly the boundary of the quantum set; for others, there is still a gap. We close some of these gaps using a new quantifier for IC, based on the notion of ``redundant information''. This progress was made possible b… ▽ More Information causality (IC) was one of the first principles that have been invoked to bound the set of quantum correlations. For some families of correlations, this principle recovers exactly the boundary of the quantum set; for others, there is still a gap. We close some of these gaps using a new quantifier for IC, based on the notion of ``redundant information''. This progress was made possible by the recognition that the principle of IC can be captured without referring to the success criterion of random access codes. We give strong numerical evidence that the new definition is still obeyed by quantum correlations in the same scenario. △ Less

Submitted 12 July, 2026; v1 submitted 22 January, 2022; originally announced January 2022.

Comments: 6 pages, 3 figures, 1 table

Journal ref: Phys. Rev. A 114, 012202 (2026)

Absolutely entangled sets of pure states for bipartitions and multipartitions

Authors: Baichu Yu, Pooja Jayachandran, Adam Burchardt, Yu Cai, Nicolas Brunner, Valerio Scarani

Abstract: A set of quantum states is said to be absolutely entangled, when at least one state in the set remains entangled for any definition of subsystems, i.e. for any choice of the global reference frame. In this work we investigate the properties of absolutey entangled sets (AES) of pure quantum states. For the case of a two-qubit system, we present a sufficient condition to detect an AES, and use it to… ▽ More A set of quantum states is said to be absolutely entangled, when at least one state in the set remains entangled for any definition of subsystems, i.e. for any choice of the global reference frame. In this work we investigate the properties of absolutey entangled sets (AES) of pure quantum states. For the case of a two-qubit system, we present a sufficient condition to detect an AES, and use it to construct families of $N$ states such that $N-3$ (the maximal possible number) remain entangled for any definition of subsystems. For a general bipartition $d=d_1d_2$, we prove that sets of $N>\left\lfloor{(d_{1}+1)(d_{2}+1)/2}\right \rfloor$ states are AES with Haar measure 1. Then, we define AES for multipartitions. We derive a general lower bound on the number of states in an AES for a given multipartition, and also construct explicit examples. In particular, we exhibit an AES with respect to any possible multi-partitioning of the total system. △ Less

Submitted 4 October, 2021; v1 submitted 30 June, 2021; originally announced June 2021.

Comments: 11 pages, 2 figures

Journal ref: Phys. Rev. A 104, 032414 (2021)

Heralded generation of vectorially structured photons with high purity

Authors: Hai-Jun Wu, Bing-Shi Yu, Zhi-Han Zhu, Carmelo Rosales-Guzmán, Zhi-Yuan Zhou, Dong-Sheng Ding, Wei Gao, Bao-Sen Shi

Abstract: Engineering vector spatial modes of photons is an important approach for manipulating high-dimension photonic states in various quantum optical experiments. In this work, we demonstrate generation of heralded single photons with well-defined vector spatial modes by using a self-locking polarizing interferometer comprising a spatial light modulator. Specifically, it is shown that, by carefully tail… ▽ More Engineering vector spatial modes of photons is an important approach for manipulating high-dimension photonic states in various quantum optical experiments. In this work, we demonstrate generation of heralded single photons with well-defined vector spatial modes by using a self-locking polarizing interferometer comprising a spatial light modulator. Specifically, it is shown that, by carefully tailoring and compensating spatial and temporal amplitudes of manipulated photons, one can exactly convert ultrafast single photons into desired spin-orbit states with extremely high purity. This compact and robust device provides a versatile way for not only generation, but also manipulation and characterization of arbitrary photonic spin-orbit states. △ Less

Submitted 17 January, 2021; originally announced January 2021.

Precise Spectroscopy of High-Frequency Oscillating Fields with a Single-Qubit Sensor

Authors: Yaoming Chu, Pengcheng Yang, Musang Gong, Min Yu, Baiyi Yu, Martin B. Plenio, Alex Retzker, Jianming Cai

Abstract: Precise spectroscopy of oscillating fields plays significant roles in many fields. Here, we propose an experimentally feasible scheme to measure the frequency of a fast-oscillating field using a single-qubit sensor. By invoking a stable classical clock, the signal phase correlations between successive measurements enable us to extract the target frequency with extremely high precision. In addition… ▽ More Precise spectroscopy of oscillating fields plays significant roles in many fields. Here, we propose an experimentally feasible scheme to measure the frequency of a fast-oscillating field using a single-qubit sensor. By invoking a stable classical clock, the signal phase correlations between successive measurements enable us to extract the target frequency with extremely high precision. In addition, we integrate dynamical decoupling technique into the framework to suppress the influence of slow environmental noise. Our framework is feasible with a variety of atomic and single solid-state-spin systems within the state-of-the-art experimental capabilities as a versatile tool for quantum spectroscopy. △ Less

Submitted 20 January, 2021; v1 submitted 11 September, 2020; originally announced September 2020.

Journal ref: Phys. Rev. Applied 15, 014031 (2021)

Dynamic framework for criticality-enhanced quantum sensing

Authors: Yaoming Chu, Shaoliang Zhang, Baiyi Yu, Jianming Cai

Abstract: Quantum criticality, as a fascinating quantum phenomenon, may provide significant advantages for quantum sensing. Here we propose a dynamic framework for quantum sensing with a family of Hamiltonians that undergo quantum phase transitions (QPT). By giving the formalism of the quantum Fisher information (QFI) for quantum sensing based on critical quantum dynamics, we demonstrate its divergent featu… ▽ More Quantum criticality, as a fascinating quantum phenomenon, may provide significant advantages for quantum sensing. Here we propose a dynamic framework for quantum sensing with a family of Hamiltonians that undergo quantum phase transitions (QPT). By giving the formalism of the quantum Fisher information (QFI) for quantum sensing based on critical quantum dynamics, we demonstrate its divergent feature when approaching the critical point. We illustrate the basic principle and the details of experimental implementation using quantum Rabi model. The framework is applicable to a variety of examples and does not rely on the stringent requirement for particular state preparation or adiabatic evolution. It is expected to provide a route towards the implementation of criticality-enhanced quantum sensing. △ Less

Submitted 19 January, 2021; v1 submitted 26 August, 2020; originally announced August 2020.

Journal ref: Phys. Rev. Lett. 126, 010502 (2021)

Entanglement for any definition of two subsystems

Authors: Yu Cai, Baichu Yu, Pooja Jayachandran, Nicolas Brunner, Valerio Scarani, Jean-Daniel Bancal

Abstract: The notion of entanglement of quantum states is usually defined with respect to a fixed bipartition. Indeed, a global basis change can always map an entangled state to a separable one. The situation is however different when considering a set of states. In this work we define the notion of an "absolutely entangled set" of quantum states: for any possible choice of global basis, at least one of the… ▽ More The notion of entanglement of quantum states is usually defined with respect to a fixed bipartition. Indeed, a global basis change can always map an entangled state to a separable one. The situation is however different when considering a set of states. In this work we define the notion of an "absolutely entangled set" of quantum states: for any possible choice of global basis, at least one of the states in the set is entangled. Hence, for all bipartitions, i.e. any possible definition of the subsystems, the set features entanglement. We present a minimum example of this phenomenon, with a set of four states in $\mathbb{C}^4 = \mathbb{C}^2 \otimes \mathbb{C}^2$. Moreover, we propose a quantitative measure for absolute set entanglement. To lower-bound this quantity, we develop a method based on polynomial optimization to perform convex optimization over unitaries, which is of independent interest. △ Less

Submitted 11 November, 2020; v1 submitted 12 June, 2020; originally announced June 2020.

Comments: Main: 5 pages, 2 figures; Appendix: 5 pages and 1 figure

Journal ref: Phys. Rev. A 103, 052432 (2021)

Distribution of spin correlation strengths in multipartite systems

Authors: Bing Yu, Naihuan Jing, Xianqing Li-Jost

Abstract: For a two-qubit state the isotropic strength measures the degree of isotropic spin correlation. The concept of isotropic strength is generalized to multipartite qudit systems, and the strength distributions for tripartite and quadripartite qudit systems are thoroughly investigated. We show that the sum of relative isotropic strengths of any three qudit state over $d$-dimensional Hilbert space cann… ▽ More For a two-qubit state the isotropic strength measures the degree of isotropic spin correlation. The concept of isotropic strength is generalized to multipartite qudit systems, and the strength distributions for tripartite and quadripartite qudit systems are thoroughly investigated. We show that the sum of relative isotropic strengths of any three qudit state over $d$-dimensional Hilbert space cannot exceed $d-1$, which generalizes of the case $d=2$. The trade-off relations and monogamy-like relations of the sum of spin correlation strengths for pure three- and four-partite systems are derived. Moreover, the bounds of spin correlation strengths among different subsystems of a quadripartite state are used to analyze quantum entanglement. △ Less

Submitted 28 September, 2019; originally announced September 2019.

Comments: 13 pages

Journal ref: Quantum Inf Process (2019) 18: 344

Strong unitary uncertainty relations

Authors: Bing Yu, Naihuan Jing, Xianqing Li-Jost

Abstract: In this paper we provide a new set of uncertainty principles for unitary operators using a sequence of inequalities with the help of the geometric-arithmetic mean inequality. As these inequalities are "fine-grained" compared with the well-known Cauchy-Schwarz inequality, our framework naturally improves the results based on the latter. As such, the unitary uncertainty relations based on our method… ▽ More In this paper we provide a new set of uncertainty principles for unitary operators using a sequence of inequalities with the help of the geometric-arithmetic mean inequality. As these inequalities are "fine-grained" compared with the well-known Cauchy-Schwarz inequality, our framework naturally improves the results based on the latter. As such, the unitary uncertainty relations based on our method outperform the best known bound introduced in [Phys. Rev. Lett. 120, 230402 (2018)] to some extent. Explicit examples of unitary uncertainty relations are provided to back our claims. △ Less

Submitted 14 August, 2019; originally announced August 2019.

Comments: 10 pages, 8 figures

Journal ref: Phys. Rev. A 100, 022116 (2019)

Measurement-device-independent quantification of irreducible high-dimensional entanglement

Authors: Yu Guo, Bai-Chu Yu, Xiao-Min Hu, Bi-Heng Liu, Yu-Chun Wu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo

Abstract: The certification of entanglement dimensionality is of great importance in characterizing quantum systems. Recently, it is pointed out that quantum correlation of high-dimensional states can be simulated with a sequence of lower-dimensional states. Such problem may render existing characterization protocols unreliable---the observed entanglement may not be a truly high-dimensional one. Here, we in… ▽ More The certification of entanglement dimensionality is of great importance in characterizing quantum systems. Recently, it is pointed out that quantum correlation of high-dimensional states can be simulated with a sequence of lower-dimensional states. Such problem may render existing characterization protocols unreliable---the observed entanglement may not be a truly high-dimensional one. Here, we introduce the notion of irreducible entanglement to capture its dimensionality that is indecomposable in terms of a sequence of lower-dimensional entangled systems. We prove this new feature can be detected in a measurement-device-independent manner with an entanglement witness protocol. To demonstrate the practicability of this technique, we experimentally apply it on a 3-dimensional bipartite state and the result certifies the existence of irreducible (at least) 3-dimensional entanglement. △ Less

Submitted 18 June, 2020; v1 submitted 4 January, 2019; originally announced January 2019.

Comments: 6 pages, 2 figures, comments are welcome

Journal ref: npj Quantum Information 6, Article number: 52 (2020)

Entropic No-Disturbance as a Physical Principle

Authors: Zhih-Ahn Jia, Rui Zhai, Bai-Chu Yu, Yu-Chun Wu, Guang-Can Guo

Abstract: The celebrated Bell-Kochen-Specker no-go theorem asserts that quantum mechanics does not present the property of realism, the essence of the theorem is the lack of a joint probability distributions for some experiment settings. In this work, we exploit the information theoretic form of the theorem using information measure instead of probabilistic measure and indicate that quantum mechanics does n… ▽ More The celebrated Bell-Kochen-Specker no-go theorem asserts that quantum mechanics does not present the property of realism, the essence of the theorem is the lack of a joint probability distributions for some experiment settings. In this work, we exploit the information theoretic form of the theorem using information measure instead of probabilistic measure and indicate that quantum mechanics does not present such entropic realism neither. The entropic form of Gleason's no-disturbance principle is developed and it turns out to be characterized by the intersection of several entropic cones. Entropic contextuality and entropic nonlocality are investigated in depth in this framework. We show how one can construct monogamy relations using entropic cone and basic Shannon-type inequalities. The general criterion for several entropic tests to be monogamous is also developed, using the criterion, we demonstrate that entropic nonlocal correlations are monogamous, entropic contextuality tests are monogamous and entropic nonlocality and entropic contextuality are also monogamous. Finally, we analyze the entropic monogamy relations for multiparty and many-test case, which plays a crucial role in quantum network communication. △ Less

Submitted 21 March, 2018; originally announced March 2018.

Journal ref: Phys. Rev. A 97, 052128 (2018)

Geometric Local Hidden State Model for Some Two-qubit States

Authors: Bai-Chu Yu, Zhih-Ahn Jia, Yu-chun Wu, Guang-Can Guo

Abstract: Adopting the geometric description of steering assemblages and local hidden states (LHS) model, we construct the optimal LHS model for some two-qubit states under continuous projective measurements, and obtain a sufficient steering criterion for all two-qubit states. Using the criterion, we show more two-qubit states that are asymmetric in steering scenario under projective measurements. Then we g… ▽ More Adopting the geometric description of steering assemblages and local hidden states (LHS) model, we construct the optimal LHS model for some two-qubit states under continuous projective measurements, and obtain a sufficient steering criterion for all two-qubit states. Using the criterion, we show more two-qubit states that are asymmetric in steering scenario under projective measurements. Then we generalize the geometric description into higher dimensional bipartite cases, calculate the steering bound of two-qutrit isotropic states and make discussion on more general cases. △ Less

Submitted 16 November, 2018; v1 submitted 18 October, 2017; originally announced October 2017.

Journal ref: Phys. Rev. A 98, 052345 (2018)

Geometric Steering Criterion for Two-qubit States

Authors: Bai-Chu Yu, Zhih-Ahn Jia, Yu-Chun Wu, Guang-Can Guo

Abstract: According to the geometric characterization of measurement assemblages and local hidden state (LHS) models, we propose a steering criterion which is both necessary and sufficient for two-qubit states under arbitrary measurement sets. A quantity is introduced to describe the required local resources to reconstruct a measurement assemblage for two-qubit states. We show that the quantity can be regar… ▽ More According to the geometric characterization of measurement assemblages and local hidden state (LHS) models, we propose a steering criterion which is both necessary and sufficient for two-qubit states under arbitrary measurement sets. A quantity is introduced to describe the required local resources to reconstruct a measurement assemblage for two-qubit states. We show that the quantity can be regarded as a quantification of steerability and be used to find out optimal LHS models. Finally we propose a method to generate unsteerable states, and construct some two-qubit states which are entangled but unsteerable under all projective measurements. △ Less

Submitted 16 November, 2018; v1 submitted 18 October, 2017; originally announced October 2017.

Journal ref: Phys. Rev. A 97, 012130 (2018)

Enhanced transmission capacity for laser communication at the single-photon level using the multi-channel frequency coding scheme

Authors: Jianyong Hu, Bo Yu, Mingyong Jing, Liantuan Xiao, Suotang Jia

Abstract: The statistical properties of a radiation sources are commonly characterized by second-order-correlation or Mandel parameter. Our research found that the single photons modulation spectrum provides us another optional way which is more sensitive to the high frequency information contained in the photon sequence. In this paper, we present direct laser communication by using a multi-channel frequenc… ▽ More The statistical properties of a radiation sources are commonly characterized by second-order-correlation or Mandel parameter. Our research found that the single photons modulation spectrum provides us another optional way which is more sensitive to the high frequency information contained in the photon sequence. In this paper, we present direct laser communication by using a multi-channel frequency coding scheme based on the single photons modulation spectrum in which the multi-frequency modulation makes the transmission capacity efficiently enhanced. The modulation frequencies could be operated in a wide band without frequency aliasing due to the inherent randomness of photons arrival time of weak coherent light. The error rate less than 10-5 has been achieved experimentally when the mean signal photon count is 80 kcps. The modulated coherent light field shows nonlinear effects of single photons modulation spectrum. The studies of statistical properties of the single photons modulation spectrum, including the dependence of mean noise photon count, integration time, channel spacing and the number of frequency component, helped us to optimize the error rate and transmission capacity. △ Less

Submitted 19 April, 2017; originally announced April 2017.

Comments: There are 11 pages, 9 figures in the paper. In this paper, we proposed a new MCFC coding scheme, which is specially designed for laser communication when the received signal is at the single-photon level

Super quantum discord for general two qubit X states

Authors: Naihuan Jing, Bing Yu

Abstract: The exact solutions of the super quantum discord are derived for general two qubit X states in terms of a one-variable function. Several exact solutions of the super quantum discord are given for the general X-state over nontrivial regions of a seven dimensional manifold. It is shown that the super quantum discord of the X state may increase or decreases under the phase damping channel. The exact solutions of the super quantum discord are derived for general two qubit X states in terms of a one-variable function. Several exact solutions of the super quantum discord are given for the general X-state over nontrivial regions of a seven dimensional manifold. It is shown that the super quantum discord of the X state may increase or decreases under the phase damping channel. △ Less

Submitted 23 February, 2017; v1 submitted 22 January, 2017; originally announced January 2017.

Comments: 16 pages, 3 figures

Journal ref: Quant. Inf. Process. 16 (2017), 16:99 (18pp.)

Near-Optimal Variance-Based Uncertainty Relations

Authors: Yunlong Xiao, Naihuan Jing, Bing Yu, Shao-Ming Fei, Xianqing Li-Jost

Abstract: Learning physical properties of a quantum system is essential for the developments of quantum technologies. However, Heisenberg's uncertainty principle constrains the potential knowledge one can simultaneously have about a system in quantum theory. Aside from its fundamental significance, the mathematical characterization of this restriction, known as `uncertainty relation', plays important roles… ▽ More Learning physical properties of a quantum system is essential for the developments of quantum technologies. However, Heisenberg's uncertainty principle constrains the potential knowledge one can simultaneously have about a system in quantum theory. Aside from its fundamental significance, the mathematical characterization of this restriction, known as `uncertainty relation', plays important roles in a wide range of applications, stimulating the formation of tighter uncertainty relations. In this work, we investigate the fundamental limitations of variance-based uncertainty relations, and introduce several `near optimal' bounds for incompatible observables. Our results consist of two morphologically distinct phases: lower bounds that illustrate the uncertainties about measurement outcomes, and the upper bound that indicates the potential knowledge we can gain. Combining them together leads to an \emph{uncertainty interval}, which captures the essence of uncertainties in quantum theory. Finally, we have detailed how to formulate lower bounds for product-form variance-based uncertainty relations by employing entropic uncertainty relations, and hence built a link between different forms of uncertainty relations. △ Less

Submitted 23 March, 2022; v1 submitted 5 October, 2016; originally announced October 2016.

Comments: 7 pages, 4 figures; Final version with new title

Journal ref: Frontiers in Physics, (2022), 10:846330

Quantum discord of X-states as optimization of one variable function

Authors: Naihuan Jing, Bing Yu

Abstract: We solve the quantum discord completely as an optimization of certain one variable function for arbitrary two qubit X state. Exact solutions of the quantum discord are obtained for several nontrivial regions of the five parametric space for the quantum state. Exceptional solutions are determined via an iterative algorithm. We solve the quantum discord completely as an optimization of certain one variable function for arbitrary two qubit X state. Exact solutions of the quantum discord are obtained for several nontrivial regions of the five parametric space for the quantum state. Exceptional solutions are determined via an iterative algorithm. △ Less

Submitted 27 July, 2016; v1 submitted 31 March, 2016; originally announced April 2016.

Comments: 17 pages. Revised version with New title, and more references are added

Journal ref: J. Phys. A: Math. Theor. 49 (2016) 385302 (16 pp)

Experimental quantum secure direct communication with single photons

Authors: Jianyong Hu, Bo Yu, Mingyong Jing, Liantuan Xiao, Suotang Jia, Guoqing Qin, Guilu Long

Abstract: Quantum communication holds promise for absolutely security in secret message transmission. Quantum secure direct communication is an important mode of the quantum communication in which secret messages are securely communicated over a quantum channel directly. It has become one of the hot research areas in the last decade, and offers both high security and instantaneousness in communication. It i… ▽ More Quantum communication holds promise for absolutely security in secret message transmission. Quantum secure direct communication is an important mode of the quantum communication in which secret messages are securely communicated over a quantum channel directly. It has become one of the hot research areas in the last decade, and offers both high security and instantaneousness in communication. It is also a basic cryptographic primitive for constructing other quantum communication tasks such as quantum authentication, quantum dialogue and so on. Here we report the first experimental demonstration of quantum secure direct communication with single photons. The experiment is based on the DL04 protocol, equipped with a simple frequency coding. It has the advantage of being robust against channel noise and loss. The experiment demonstrated explicitly the block data transmission technique, which is essential for quantum secure direct communication. In the experiment, a block transmission of 80 single photons was demonstrated over fiber, and it provides effectively 16 different values, which is equivalent to 4 bits of direct transmission in one block. The experiment has firmly demonstrated the feasibility of quantum secure direct communication in the presence of noise and loss. △ Less

Submitted 7 September, 2015; v1 submitted 2 March, 2015; originally announced March 2015.

Comments: 21 pages, 4 figures

Electronic Transport in Monolayer Graphene with Extreme Physical Deformation: ab Initio Density Functional Calculation

Authors: Haiyuan Gao, Yang Xu, Meijiao Li, Zhendong Guo, Hongshen Chen, Zhonghe Jin, Bin Yu

Abstract: Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local de… ▽ More Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips. △ Less

Submitted 27 January, 2011; originally announced January 2011.

Comments: 8 pages, 4 figures

Study of Phonon Modes in Germanium Nanowires

Authors: Xi Wang, Ali Shakouri, Bin Yu, Xuhui Sun, Meyya Meyyappan

Abstract: The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We ha… ▽ More The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nanowires for the first time. △ Less

Submitted 24 February, 2007; originally announced February 2007.

Comments: 11 pages,15 figures

Remote Preparation of Mixed States via Noisy Entanglement

Authors: Guo-Yong Xiang, Jian Li, Bo Yu, Guang-Can Guo

Abstract: We present a practical and general scheme of remote preparation for pure and mixed state, in which an auxiliary qubit and controlled-NOT gate are used. We discuss the remote state preparation (RSP) in two important types of decoherent channel (depolarizing and dephaseing). In our experiment, we realize RSP in the dephaseing channel by using spontaneous parametric down conversion (SPDC), linear o… ▽ More We present a practical and general scheme of remote preparation for pure and mixed state, in which an auxiliary qubit and controlled-NOT gate are used. We discuss the remote state preparation (RSP) in two important types of decoherent channel (depolarizing and dephaseing). In our experiment, we realize RSP in the dephaseing channel by using spontaneous parametric down conversion (SPDC), linear optical elements and single photon detector. △ Less

Submitted 9 March, 2005; originally announced March 2005.

Comments: 10 pages, 5 figures, submitted to PRA

Journal ref: Proc. of SPIE Vol.5631-23, 112; Phys. Rev. A 72, 012315 (2005).

Scalable fault-tolerant quantum computation in DFS blocks

Authors: Zheng-Wei Zhou, Bo Yu, Xingxiang Zhou, Marc J. Feldman, Guang-Can Guo

Abstract: We investigate how to concatenate different decoherence-free subspaces (DFSs) to realize scalable universal fault-tolerant quantum computation. Based on tunable $XXZ$ interactions, we present an architecture for scalable quantum computers which can fault-tolerantly perform universal quantum computation by manipulating only single type of parameter. By using the concept of interaction-free subspa… ▽ More We investigate how to concatenate different decoherence-free subspaces (DFSs) to realize scalable universal fault-tolerant quantum computation. Based on tunable $XXZ$ interactions, we present an architecture for scalable quantum computers which can fault-tolerantly perform universal quantum computation by manipulating only single type of parameter. By using the concept of interaction-free subspaces we eliminate the need to tune the couplings between logical qubits, which further reduces the technical difficulties for implementing quantum computation. △ Less

Submitted 29 July, 2004; originally announced July 2004.

Comments: 4 papges, 2 figures

Journal ref: Phys. Rev. Lett. 93, 010501(2004)

Concatenating dynamical decoupling with decoherence-free subspaces for quantum computation

Authors: Yong Zhang, Zheng-Wei Zhou, Bo Yu, Guang-Can Guo

Abstract: A scheme to implement a quantum computer subjected to decoherence and governed by an untunable qubit-qubit interaction is presented. By concatenating dynamical decoupling through bang-bang (BB) pulse with decoherence-free subspaces (DFSs) encoding, we protect the quantum computer from environment-induced decoherence that results in quantum information dissipating into the environment. For the in… ▽ More A scheme to implement a quantum computer subjected to decoherence and governed by an untunable qubit-qubit interaction is presented. By concatenating dynamical decoupling through bang-bang (BB) pulse with decoherence-free subspaces (DFSs) encoding, we protect the quantum computer from environment-induced decoherence that results in quantum information dissipating into the environment. For the inherent qubit-qubit interaction that is untunable in the quantum system, BB control plus DFSs encoding will eliminate its undesired effect which spoils quantum information in qubits. We show how this quantum system can be used to implement universal quantum computation. △ Less

Submitted 11 May, 2004; v1 submitted 11 November, 2003; originally announced November 2003.

Comments: 6 pages,2 figures, 1 table

Journal ref: Phys.Rev.A 69,042315(2004)

Robust high-fidelity teleportation of an atomic state through the detection of cavity decay

Authors: Bo Yu, Zheng-Wei Zhou, Yong Zhang, Guo-Yong Xiang, Guang-Can Guo

Abstract: We propose a scheme for quantum teleportation of an atomic state based on the detection of cavity decay. The internal state of an atom trapped in a cavity can be disembodiedly transferred to another atom trapped in a distant cavity by measuring interference of polarized photons through single-photon detectors. In comparison with the original proposal by S. Bose, P.L. Knight, M.B. Plenio, and V.… ▽ More We propose a scheme for quantum teleportation of an atomic state based on the detection of cavity decay. The internal state of an atom trapped in a cavity can be disembodiedly transferred to another atom trapped in a distant cavity by measuring interference of polarized photons through single-photon detectors. In comparison with the original proposal by S. Bose, P.L. Knight, M.B. Plenio, and V. Vedral [Phys. Rev. Lett. 83, 5158 (1999)], our protocol of teleportation has a high fidelity of almost unity, and inherent robustness, such as the insensitivity of fidelity to randomness in the atom's position, and to detection inefficiency. All these favorable features make the scheme feasible with the current experimental technology. △ Less

Submitted 8 November, 2003; originally announced November 2003.

Comments: 6 pages, 5 figures

Orbital angular momentum of the down converted photons

Authors: Xi-Feng Ren, Guo-Ping Guo, Bo Yu, Jian Li, Guang-Can Guo

Abstract: We calculate the relative amplitude of orbital angular momentum (OAM) entangled photon pairs from the spontaneous parametric down conversion. The results show that the amplitude depends on both the two Laguerre indices l, p. We also discuss the influences of the mostly used holograms and mono-mode fibers for mode analyzation. We conclude that only a few dimensions can be explored from the infini… ▽ More We calculate the relative amplitude of orbital angular momentum (OAM) entangled photon pairs from the spontaneous parametric down conversion. The results show that the amplitude depends on both the two Laguerre indices l, p. We also discuss the influences of the mostly used holograms and mono-mode fibers for mode analyzation. We conclude that only a few dimensions can be explored from the infinite OAM modes of the down-converted photon pairs. △ Less

Submitted 3 September, 2003; originally announced September 2003.

Comments: 5 pages, 2 figures, 3 tables