arXiv subjects

Zhe Sun

Publications and source records attributed to Zhe Sun.

At least 163 records · Page 9Linked to original sources

arXiv2018

Electron-Doping Induced Semiconductor to Metal Transitions in ZrSe2 Layers via Copper Atomic Intercalation

Atomic intercalation in two dimensional (2D) layered materials can engineer the electronic structure at the atomic scale, bringing out tunable physical and chemical properties which are quite distinct in comparison with pristine one. Among them, electron-doped engineering induced by intercalation is an efficient route to modulate electronic states in 2D layers. Herein, we demonstrate a semiconducting to the metallic phase transition in zirconium diselenide (ZrSe2) single crystal via controllable incorporation of copper (Cu) atoms. Combined with first-principles density functional theory (DFT) calculations, our angle resolved photoemission spectroscopy (ARPES) characterizations clearly revealed the emergence of conduction band dispersion at M/L point of Brillouin zone due to Cu-induced electron doping in ZrSe2 interlayers. Moreover, the field-effect transistor (FET) fabricated on ZrSe2 displayed a n-type semiconducting transport behavior, while the Cu-intercalated ZrSe2 posed linear Ids vs Vds curves with metallic character shows n-type doping. The atomic intercalation approach has high potential for realizing transparent electron-doping systems for many specific 2D-based nano-electronics.

cond-mat.str-el↗

arXiv2018

Topological Phase Transition-Induced Tri-Axial Vector Magnetoresistance in (Bi1-xInx)2Se3 Nanodevices

We report the study of a tri-axial vector magnetoresistance (MR) in nonmagnetic (Bi1-xInx)2Se3 nanodevices at the composition of x = 0.08. We show a dumbbell-shaped in-plane negative MR up to room temperature as well as a large out-of-plane positive MR. MR at three directions is about in a -3%: -1%: 225% ratio at 2 K. Through both the thickness and composition-dependent magnetotransport measurements, we show that the in-plane negative MR is due to the topological phase transition enhanced intersurface coupling near the topological critical point. Our devices suggest the great potential for room-temperature spintronic applications, for example, vector magnetic sensors.

physics.app-ph↗

arXiv2017

Approaching the Type-II Dirac Point and Concomitant Superconductivity in Pt-doping Stabilized Metastable 1T-phase IrTe2

Topological semimetal is a topic of general interest in material science. Recently, a new kind of topological semimetal called type-II Dirac semimetal with tilted Dirac cones is discovered in PtSe2 family. However, the further investigation is hindered due to the huge energy difference from Dirac points to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we characterize the optimized type-II Dirac dispersions in a metastable 1T phase of IrTe2. Our strategy of Pt doping protects the metastable 1T phase in low temperature and tunes the Fermi level to the Dirac point. As demonstrated by angle-resolved photoemission spectra and first principle calculations, the Fermi surface of Ir1-xPtxTe2 is formed by only a single band with type-II Dirac cone which is tilted strongly along kz momentum direction. Interesting superconductivity is observed in samples for Dirac point close to Fermi level and even survives when Fermi level aligns with the Dirac point as finite density of states created by the tilted cone dispersion. This advantage offers opportunities for possible topological superconductivity and versatile Majorana devices in type-II Dirac semimetals.

cond-mat.mtrl-sci↗

arXiv2017

Quantum interface between photonic and superconducting qubits

We show that optically active coupled quantum dots embedded in a superconducting microwave cavity can be used to realize a fast quantum interface between photonic and transmon qubits. Single photon absorption by a coupled quantum dot results in generation of a large electric dipole, which in turn ensures efficient coupling to the microwave cavity. Using cavity parameters achieved in prior experiments, we estimate that bi-directional microwave-optics conversion in nanosecond timescales with efficiencies approaching unity is experimentally feasible with current technology. We also outline a protocol for in-principle deterministic quantum state transfer from a time-bin photonic qubit to a transmon qubit. Recent advances in quantum dot based quantum photonics technologies indicate that the scheme we propose could play a central role in connecting quantum nodes incorporating cavity-coupled superconducting qubits.

quant-ph↗

arXiv2017

$\ell_1$-minimization method for link flow correction

A computational method, based on $\ell_1$-minimization, is proposed for the problem of link flow correction, when the available traffic flow data on many links in a road network are inconsistent with respect to the flow conservation law. Without extra information, the problem is generally ill-posed when a large portion of the link sensors are unhealthy. It is possible, however, to correct the corrupted link flows \textit{accurately} with the proposed method under a recoverability condition if there are only a few bad sensors which are located at certain links. We analytically identify the links that are robust to miscounts and relate them to the geometric structure of the traffic network by introducing the recoverability concept and an algorithm for computing it. The recoverability condition for corrupted links is simply the associated recoverability being greater than 1. In a more realistic setting, besides the unhealthy link sensors, small measurement noises may be present at the other sensors. Under the same recoverability condition, our method guarantees to give an estimated traffic flow fairly close to the ground-truth data and leads to a bound for the correction error. Both synthetic and real-world examples are provided to demonstrate the effectiveness of the proposed method.

cs.IT↗

arXiv2017

Electronic band structure of epitaxial PbTe (111) thin films observed by angle-resolved photoemission spectroscopy

Using angle-resolved photoemission spectroscopy (ARPES), we studied bulk and surface electronic band structures of narrow-gap semiconductor lead telluride (PbTe) thin films grown by molecular beam epitaxy both perpendicular and parallel to the Γ-L direction. The comparison of ARPES data with the first-principles calculation reveals the details of band structures, orbital characters, spin-orbit splitting energies, and surface states. The photon-energy-dependent spectra show the bulk character. Both the L and Σ valence bands are observed and their energy difference is determined. The spin-orbit splitting energies at L and Γ points are 0.62 eV and 0.88 eV, respectively. The surface states below and close to the valence band maximum are identified. The valence bands are composed of a mixture of Pb 6s and Te $5p_z$ orbitals with dominant in-plane even parity, which is attributed to the layered distortion in the vicinity of PbTe (111) surface. These findings provide insights into PbTe fundamental properties and shall benefit relevant thermoelectric and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2017

DIMM-SC: A Dirichlet mixture model for clustering droplet-based single cell transcriptomic data

Motivation: Single cell transcriptome sequencing (scRNA-Seq) has become a revolutionary tool to study cellular and molecular processes at single cell resolution. Among existing technologies, the recently developed droplet-based platform enables efficient parallel processing of thousands of single cells with direct counting of transcript copies using Unique Molecular Identifier (UMI). Despite the technology advances, statistical methods and computational tools are still lacking for analyzing droplet-based scRNA-Seq data. Particularly, model-based approaches for clustering large-scale single cell transcriptomic data are still under-explored. Methods: We developed DIMM-SC, a Dirichlet Mixture Model for clustering droplet-based Single Cell transcriptomic data. This approach explicitly models UMI count data from scRNA-Seq experiments and characterizes variations across different cell clusters via a Dirichlet mixture prior. An expectation-maximization algorithm is used for parameter inference. Results: We performed comprehensive simulations to evaluate DIMM-SC and compared it with existing clustering methods such as K-means, CellTree and Seurat. In addition, we analyzed public scRNA-Seq datasets with known cluster labels and in-house scRNA-Seq datasets from a study of systemic sclerosis with prior biological knowledge to benchmark and validate DIMM-SC. Both simulation studies and real data applications demonstrated that overall, DIMM-SC achieves substantially improved clustering accuracy and much lower clustering variability compared to other existing clustering methods. More importantly, as a model-based approach, DIMM-SC is able to quantify the clustering uncertainty for each single cell, facilitating rigorous statistical inference and biological interpretations, which are typically unavailable from existing clustering methods.

stat.ML↗

arXiv2017

Experimental simulation of quantum temporal steering beyond rotating-wave approximation

Characterizing the dynamics of open systems usually starts with a perturbative theory and involves various approximations, such as the Born, Markov and rotating-wave approximation (RWA). However, the approximation approaches could introduce more or less incompleteness in describing the bath behaviors. Here, we consider a quantum channel, which is modeled by a qubit (a two-level system) interacting with a bosonic bath. Unlike the traditional works, we experimentally simulate the system-bath interaction without applying the Born, Markov, and rotating-wave approximations. To our knowledge, this is the first experimental simulation of the quantum channels without any approximations mentioned above, by using linear optical devices. The results are quite useful and interesting, which not only reveal the effect of the counter-rotating terms but also present a more accurate picture of the quantum channel dynamics. Besides, we experimentally investigate the dynamics of the quantum temporal steering (TS), i.e., a temporal analogue of Einstein-Podolsky-Rosen steering. The experimental and theoretical results are in good agreement and show that the counter-rotating terms significantly influence the TS dynamics. When one monogamously associates TS with the security of the cryptographic protocols (e.g., BB84), our experimental tests reveal that the channels based on RWA will provide exaggerated security durations, while they are actually insecure in non-RWA channel cases. This implies that doing RWA may result in a risk for the security of quantum key distribution. Our findings are expected to have useful applications in secure quantum communications and future interesting TS studies.

quant-ph↗

arXiv2017

Experimental evidence of type-II Dirac fermions in PtSe2

Topological semimetals have attracted extensive research interests for realizing condensed matter physics counterparts of three-dimensional Dirac and Weyl fermions, which were originally introduced in high energy physics. Recently it has been proposed that type-II Dirac semimetal can host a new type of Dirac fermions which break Lorentz invariance and therefore does not have counterpart in high energy physics. Here we report the electronic structure of high quality PtSe$_2$ crystals to provide direct evidence for the existence of three-dimensional type-II Dirac fermions. A comparison of the crystal, vibrational and electronic structure to a sister compound PtTe$_2$ is also discussed. Our work provides an important platform for exploring the novel quantum phenomena in the PtSe$_2$ class of type-II Dirac semimetals.

cond-mat.mtrl-sci↗

arXiv2017

Coexistence of localized and itinerant magnetism in intercalated iron-selenide (Li,Fe)OHFeSe

The electronic structure and magnetism of a new magnetic intercalation compound (Li0.8Fe0.2)OHFeSe are investigated theoretically. The electronic structure calculations predict that the Fe in the (Li,Fe)OH intercalated layer is in +2 valence state, i.e. there is electron doping to the FeSe layer, resulting in the shrinking of the Fermi surface (FS) pocket around Gamma and a strong suppression of dynamical spin susceptibility at M in comparison with the bulk FeSe compound. The ground state of the FeSe layer is a striped antiferromagnetic (SAFM) metal, while the (Li,Fe)OH layer displays a very weak localized magnetism, with an interlayer ferromagnetic (FM) coupling between the FeSe and intercalated (Li,Fe)OH layers. Moreover, the (Li,Fe)OH is more than a block layer; it is responsible for enhancing the antiferromagnetic (AFM) correlation in the FeSe layer through interlayer magnetic coupling. We propose that the magnetic spacer layer introduces a tuning mechanism for spin fluctuations associated with superconductivity in iron-based superconductors.

cond-mat.str-el↗

arXiv2017

Realization of a cascaded quantum system: heralded absorption of a single photon qubit by a single-electron charged quantum dot

Photonic losses pose a major limitation for implementation of quantum state transfer between nodes of a quantum network. A measurement that heralds successful transfer without revealing any information about the qubit may alleviate this limitation. Here, we demonstrate heralded absorption of a single photonic qubit generated by a single neutral quantum dot, by a single-electron charged quantum dot that is located 5 meters away. The transfer of quantum information to the spin degree of freedom takes place upon emission of a photon: for a properly chosen or prepared quantum dot, detection of this photon yields no information about the qubit. We show that this process can be combined with local operations optically performed on the destination node, by measuring classical correlations between the absorbed photon color and the final state of the electron spin. Our work suggests alternative avenues for realization of quantum information protocols based on cascaded quantum systems.

quant-ph↗

arXiv2016

Swapping algebra, Virasoro algebra and discrete integrable system

We induce a Poisson algebra $\{\cdot,\cdot\}_{\mathcal{C}_{n,N}}$ on the configuration space $\mathcal{C}_{n,N}$ of $N$ twisted polygons in $\mathbb{RP}^{n-1}$ from the swapping algebra \cite{L12}, which is found coincide with Faddeev-Takhtajan-Volkov algebra for $n=2$. There is another Poisson algebra $\{\cdot,\cdot\}_{S2}$ on $\mathcal{C}_{2,N}$ induced from the first Adler-Gelfand-Dickey Poissson algebra by Miura transformation. By observing that these two Poisson algebras are asymptotically related to the dual to the Virasoro algebra, finally, we prove that $\{\cdot,\cdot\}_{\mathcal{C}_{2,N}}$ and $\{\cdot,\cdot\}_{S2}$ are Schouten commute.

math.DG↗

arXiv2016

Lorentz-violating type-II Dirac fermions in transition metal dichalcogenide PtTe$_2$

Topological semimetals have recently attracted extensive research interests as host materials to condensed matter physics counterparts of Dirac and Weyl fermions originally proposed in high energy physics. These fermions with linear dispersions near the Dirac or Weyl points obey Lorentz invariance, and the chiral anomaly leads to novel quantum phenomena such as negative magnetoresistance. The Lorentz invariance is, however, not necessarily respected in condensed matter physics, and thus Lorentz-violating type-II Dirac fermions with strongly tilted cones can be realized in topological semimetals. Here, we report the first experimental evidence of type-II Dirac fermions in bulk stoichiometric PtTe$_2$ single crystal. Angle-resolved photoemission spectroscopy (ARPES) measurements and first-principles calculations reveal a pair of strongly tilted Dirac cones along the $Γ$-A direction under the symmetry protection, confirming PtTe$_2$ as a type-II Dirac semimetal. The realization of type-II Dirac fermions opens a new door for exotic physical properties distinguished from type-I Dirac fermions in condensed matter materials.

cond-mat.mtrl-sci↗

arXiv2016

Measurement of spin coherence using Raman scattering

Ramsey interferometry provides a natural way to determine the coherence time of most qubit systems. Recent experiments on quantum dots however, demonstrated that dynamical nuclear spin polarization can strongly influence the measurement process, making it difficult to extract the $T_2^*$ coherence time using optical Ramsey pulses. Here, we demonstrate an alternative method for spin coherence measurement that is based on first-order coherence of photons generated in spin-flip Raman scattering. We show that if a quantum emitter is driven by a weak monochromatic laser, Raman coherence is determined exclusively by spin coherence, allowing for a direct determination of spin $T_2^*$ time. When combined with coherence measurements on Rayleigh scattered photons, our technique enables us to identify coherent and incoherent contributions to resonance fluorescence, and to minimize the latter. We verify the validity of our technique by comparing our results to those determined from Ramsey interferometry for electron and heavy-hole spins.

quant-ph↗

arXiv2016

Quantum multiparameter metrology with generalized entangled coherent state

We propose a generalized form of entangled coherent states (ECS) and apply them in a multi-arm optical interferometer to estimate multiple phase shifts. We obtain the quantum Cramer-Rao bounds for both the linear and nonlinear parameterization protocols. Through the analysis, we find that, utilizing the simultaneous estimation, this generalized form of ECS gives a better precision than the generalized NOON states [Phys. Rev. Lett. \textbf{111}, 070403 (2013)]. Moreover, comparing with the independent estimation, both the linear and nonlinear protocols have the same advantage in the relation to the number of the parameters.

quant-ph↗

arXiv2015

Finite-time Landau-Zener processes and counter-diabatic driving in open systems: beyond Born, Markov and Rotating-wave approximations

We investigate Landau-Zener processes modeled by a two-level quantum system, with its finite bias energy varied in time and in the presence of a single broadened cavity mode at zero temperature. By applying the hierarchy equation method to the Landau-Zener problem, we computationally study the survival fidelity of adiabatic states without Born, Markov, rotating-wave or other perturbative approximations. With this treatment it also becomes possible to investigate cases with very strong system-bath coupling. Different from a previous study of infinite-time Landau-Zener processes, the fidelity of the time-evolving state as compared with instantaneous adiabatic states shows non-monotonic dependence on the system-bath coupling and on the sweep rate of the bias. We then consider the effect of applying a counter-diabatic driving field, which is found to be useful in improving the fidelity only for sufficiently short Landau-Zener processes. Numerically exact results show that different counter-diabatic driving fields can have much different robustness against environment effects. Lastly, using a case study we discuss the possibility of introducing a dynamical decoupling field in order to eliminate the decoherence effect of the environment and at the same time to retain the positive role of a counter-diabatic field. Our work indicates that finite-time Landau-Zener processes with counter-diabatic driving offer a fruitful test bed to understand controlled adiabatic processes in open systems.

quant-ph↗

arXiv2015

Rank $n$ swapping algebra for the $\operatorname{PSL}(n, \mathbb{R})$ Hitchin component

F. Labourie [arXiv:1212.5015] characterized the Hitchin components for $\operatorname{PSL}(n, \mathbb{R})$ for any $n>1$ by using the swapping algebra, where the swapping algebra should be understood as a ring equipped with a Poisson bracket. We introduce the rank $n$ swapping algebra, which is the quotient of the swapping algebra by the $(n+1)\times(n+1)$ determinant relations. The main results are the well-definedness of the rank $n$ swapping algebra and the "cross-ratio" in its fraction algebra. As a consequence, we use the sub fraction algebra of the rank $n$ swapping algebra generated by these "cross-ratios" to characterize the $\operatorname{PSL}(n, \mathbb{R})$ Hitchin component for a fixed $n>1$. We also show the relation between the rank $2$ swapping algebra and the cluster $\mathcal{X}_{\operatorname{PGL}(2,\mathbb{R}),D_k}$-space.

math.DG↗

arXiv2015

Efficient scheme for generation of photonic NOON states in circuit QED

We propose an efficient scheme for generating photonic NOON states of two resonators coupled to a four-level superconducting flux device. This proposal operates essentially by employing a technique of a coupler device resonantly interacting with two resonators simultaneously. As a consequence, the NOON-state preparation requires only $N+1$ operational steps and thus is much faster when compared with a recent proposal [Q. P. Su et al., Scientific Reports 4, 3898 (2014)] requiring $2N$ steps of operation. Moreover, due to the use of only two resonators and a device, the experimental setup is much simplified when compared with previous proposals requiring three resonators and two superconducting qubits/qutrits.

quant-ph↗