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Xiaoguang Wang

Publications and source records attributed to Xiaoguang Wang.

At least 109 records · Page 6Linked to original sources
arXiv2013

Phase matching condition for enhancement of phase sensitivity in quantum metrology

We find a phase matching condition for enhancement of sensitivity in a Mach-Zehnder interferometer illuminated by an arbitrary state in one input port and an odd(even) state in the other port. Under this condition, the Fisher information becomes maximal with respect to the relative phase of two modes and the phase sensitivity is enhanced. For the case with photon losses, we further find that the phase matching condition keeps unchanged with a coherent state and a coherent superposition state as the input states.

quant-ph↗
arXiv2013

Quantum Fisher Information of Entangled Coherent States in a Lossy Mach-Zehnder Interferometer

We give an analytical result for the quantum Fisher information of entangled coherent States in a lossy Mach-Zehnder Interferometer recently proposed by J. Joo et al. [Phys. Rev. Lett. 107, 083601(2011)]. For small loss of photons, we find that the entangled coherent state can surpass the Heisenberg limit. Furthermore, The formalism developed here is applicable to the study of phase sensitivity of multipartite entangled coherent states.

quant-ph↗
arXiv2013

Dephasing-assisted parameter estimation in the presence of dynamical decoupling

We study the dephasing-assisted precision of parameter estimation (PPE) enhancement in atom interferometer under dynamical decoupling (DD) pulses. Through calculating spin squeezing (SS) and quantum Fisher information (QFI), we find that dephasing noise can improve PPE by inducing SS, and the DD pulses can maximize the improvement. It is indicated that in the presence of DD pulses, the dephasing-induced SS can reach the limit of \textquotedblleft one-axis twisting\textquotedblright\ model, $ξ^2\simeq N^{-2/3}$ with $ξ^2$ being the SS parameter and N the number of atoms. In particular, we find that the DD pulses can amplify the dephasing-induced QFI by a factor of $\simeq N/2$ compared with the noise-free case, which means that under the control of DD pulses, the dephasing noise can enhance the PPE to the scale of $\sqrt{2}/N$, the same order of magnitude of Heisenberg limit (1/N).

quant-ph↗
arXiv2013

Broadcasting Quantum Fisher Information

It is well known that classical information can be cloned, but non-orthogonal quantum states cannot be cloned, and non-commuting quantum states cannot be broadcast. We conceive a scenario in which the object we want to broadcast is the statistical distinguishability, as quantified by quantum Fisher information, about a signal parameter encoded in quantum states. We show that quantum Fisher information cannot be cloned, whilst it might be broadcast even when the input states are non-commuting. This situation interpolates between cloning of classical information and no-broadcasting of quantum information, and indicates a hybrid way of information broadcasting which is of particular significance from both practical and theoretical perspectives.

quant-ph↗
arXiv2013

Non-unital non-Markovianity of quantum dynamics

We show that Breuer-Laine-Piilo (BLP) non-Markovianity cannot capture the dynamical information in the non-unital aspect of the quantum dynamics. Moreover, we provide a measure on the effect of the non-unitality of quantum processes on the infinitesimal non-divisibility. This measure can be used as a supplement to BLP non-Markovianity for non-unital quantum processes. A measure on the degree of the non-unital behavior of quantum processes is also given in this paper.

quant-ph↗
arXiv2013

Fisher information under decoherence in Bloch representation

The dynamics of two variants of quantum Fisher information under decoherence are investigated from a geometrical point of view. We first derive the explicit formulas of these two quantities for a single qubit in terms of the Bloch vector. Moreover, we obtain analytical results for them under three different decoherence channels, which are expressed as affine transformation matrices. Using the hierarchy equation method, we numerically study the dynamics of both the two information in a dissipative model and compare the numerical results with the analytical ones obtained by applying the rotating-wave approximation. We further express the two information quantities in terms of the Bloch vector for a qudit, by expanding the density matrix and Hermitian operators in a common set of generators of the Lie algebra $\mathfrak{su}(d)$. By calculating the dynamical quantum Fisher information, we find that the collisional dephasing significantly diminishes the precision of phase parameter with the Ramsey interferometry.

quant-ph↗
arXiv2013

Conjugacy between polynomial basins

In this article, we study the properties of conjugacies between polynomial basins. For any conjugacy, there is a quasiconformal conjugacy in the same homotopy class minimizing the dilatation. We compute the precise value of the minimal dilatation. The quasiconformal conjugacy minimizing the dilatation is not unique in general. We give a necessary and sufficient condition when the extremal map is unique.

math.DS↗
arXiv2012

Hyperbolic components of McMullen maps

In this article, we study the hyperbolic components of McMullen maps. We show that the boundaries of all hyperbolic components are Jordan curves. This settles a problem posed by Devaney. As a consequence, we show that cusps are dense on the boundary of the unbounded hyperbolic component. This is a dynamical analogue of McMullen's theorem that cusps are dense on the Bers' boundary of Teichmüller space.

math.DS↗
arXiv2012

Photon-assisted Landau-Zener transition: Role of coherent superposition states

We investigate a Landau-Zener (LZ) transition process modeled by a quantum two-level system (TLS) coupled to a photon mode when the bias energy is varied linearly in time. The initial state of the photon field is assumed to be a superposition of coherent states, leading to a more intricate LZ transition. Applying the rotating-wave approximation (RWA), analytical results are obtained revealing the enhancement of the LZ probability by increasing the average photon number. We also consider the creation of entanglement and the change of photon statistics during the LZ process. Without the RWA, we find some qualitative differences of the LZ dynamics from the RWA results, e.g., the average photon number no longer monotonically enhances the LZ probability. The ramifications and implications of these results are explored.

quant-ph↗
arXiv2012

Entanglement Dynamics of Two Qubits in a Common Bath

We derive a set of hierarchical equations for qubits interacting with a Lorentz-broadened cavity mode at zero temperature, without using the rotating-wave, Born, and Markovian approximations. We use this exact method to reexamine the entanglement dynamics of two qubits interacting with a common bath, which was previously solved only under the rotating-wave and single-excitation approximations. With the exact hierarchy equation method used here, we observe significant differences in the resulting physics, compared to the previous results with various approximations. Double excitations due to counter-rotating-wave terms are also found to have remarkable effects on the dynamics of entanglement.

quant-ph↗
arXiv2012

Macroscopic quantum coherence in spinor condensates confined in an anisotropic potential

We investigate the macroscopic quantum coherence of a spin-1 Rb condensate confined in an anisotropic potential. Under the single-mode approximation, we show that the system can be modeled as a biaxial quantum magnet due to the interplay between the magnetic dipole-dipole interaction and the anisotropic potential. By applying a magnetic field along the hard-axis, we show that the tunneling splitting oscillates as a function of the field strength. We also propose an experimental scheme to detect the oscillatory behavior of the tunneling splitting by employing the Landau-Zener tunneling.

cond-mat.quant-gas↗
arXiv2012

Necessary and sufficient condition for saturating the upper bound of quantum discord

We revisit the upper bound of quantum discord given by the von Neumann entropy of the measured subsystem. Using the Koashi-Winter relation, we obtain a trade-off between the amount of classical correlation and quantum discord in the tripartite pure states. The difference between the quantum discord and its upper bound is interpreted as a measure on the classical correlative capacity. Further, we give the explicit characterization of the quantum states saturating the upper bound of quantum discord, through the equality condition for the Araki-Lieb inequality. We also demonstrate that the saturating of the upper bound of quantum discord precludes any further correlation between the measured subsystem and the environment.

quant-ph↗
arXiv2012

Measurement-induced nonlocality based on the relative entropy

We quantify the measurement-induced nonlocality [Luo and Fu, Phys. Rev. Lett. 106, 120401 (2011)] from the perspective of the relative entropy. This quantification leads to an operational interpretation for the measurementinduced nonlocality, namely, it is the maximal entropy increase after the locally invariant measurements. The relative entropy of nonlocality is upper bounded by the entropy of the measured subsystem. We establish a relationship between the relative entropy of nonlocality and the geometric nonlocality based on the Hilbert- Schmidt norm, and show that it is equal to the maximal distillable entanglement. Several trade-off relations are obtained for tripartite pure states. We also give explicit expressions for the relative entropy of nonlocality for Bell-diagonal states.

quant-ph↗
arXiv2012

Fisher information manifestation of dynamical stability and transition to self-trapping for Bose-Einstein condensates

We investigate dynamical stability and self-trapping for Bose-Einstein condensates in a symmetric double well. The relation between the quantum Fisher information and the stability of the fixed point is studied. We find that the quantum Fisher information displays a sharp transition as the fixed point evolving from stable to unstable regime. Moreover, the transition from Josephson oscillation to self-trapping is accompanied by an abrupt change of the quantum Fisher information.

quant-ph↗
arXiv2012

Dynamics of McMullen maps

In this article, we develop the Yoccoz puzzle technique to study a family of rational maps termed McMullen maps. We show that the boundary of the immediate basin of infinity is always a Jordan curve if it is connected. This gives a positive answer to a question of Devaney. Higher regularity of this boundary is obtained in almost all cases. We show that the boundary is a quasi-circle if it contains neither a parabolic point nor a recurrent critical point. For the whole Julia set, we show that the McMullen maps have locally connected Julia sets except in some special cases.

math.DS↗
arXiv2012

Spin Squeezing under Non-Markovian Channels by Hierarchy Equation Method

We study spin squeezing under non-Markovian channels, and consider an ensemble of $N$ independent spin-1/2 particles with exchange symmetry. Each spin interacts with its own bath, and the baths are independent and identical. For this kind of open system, the spin squeezing under decoherence can be investigated from the dynamics of the local expectations, and the multi-qubit dynamics can be reduced into the two-qubit one. The reduced dynamics is obtained by the hierarchy equation method, which is a exact without rotating-wave and Born-Markov approximation. The numerical results show that the spin squeezing displays multiple sudden vanishing and revival with lower bath temperature, and it can also vanish asymptotically.

quant-ph↗
arXiv2012

A decomposition theorem for Herman maps

In 1980s, Thurston established a topological characterization theorem for postcritically finite rational maps. In this paper, a decomposition theorem for a class of postcritically infinite branched covering termed `Herman map' is developed. It's shown that every Herman map can be decomposed along a stable multicurve into finitely many Siegel maps and Thurston maps, such that the combinations and rational realizations of these resulting maps essentially dominate the original one. This result gives an answer to a problem of McMullen in a sense and enables us to prove a Thurston-type theorem for rational maps with Herman rings.

math.DS↗