arXiv subjects

D. L. Zhou

Publications and source records attributed to D. L. Zhou.

At least 55 records · Page 3Linked to original sources

arXiv2016

Configuration dependent reflection induced by dissipated localized modes

We study the one photon scattering problem for a super cavity (SC) coupling with two two-level atoms. With atomic decay, we find a sudden drop in reflection at $Δ=0$ for the two atoms in the node-antinode configuration but not in the antinode-node one. The underlying mechanism is due to the scatterer has a configuration dependent localized dissipated eigen-mode at $Δ=0$. In the node-antinode configuration, the eigen-mode localized near the input side, which can transport the photon into the SC. By exciting the atom at the node, the photon can leak into the reservoir due to atomic decay, which causes the sudden drop at $Δ=0$ in reflection. In the antinode-node case, however, the eigen-mode is localized near the output side, no photon can be transported into the SC and leads to completely reflection at $Δ=0$. A similar phenomenon has been observed in a recent experiment of X-ray quantum optics [Nature \textbf{482}, 199 (2012)] but with a much more complicated explanation due to electromagnetically induced transparency.

quant-ph↗

arXiv2016

Hysteresis in a Superfluid Atom Circuit

The energy band structure of a rotating BEC with a link in a quasi-one-dimensional torus and the role of dissipation is studied. Through this study we are able to give a microscopic interpretation of hysteresis recently observed in the experiment and we confirm that the hysteresis is the result of the presence of metastable state. We consider of both the adiabatic change and the instantaneous change of the rotation, and exhibit the differences between them. It is found that the sharp and size of the hysteresis loop change drastically with the strength of the link.

cond-mat.quant-gas↗

arXiv2016

Quantification of Symmetry

Symmetry is conventionally described in a contrariety manner that the system is either completely symmetric or completely asymmetric. Using group theoretical approach to overcome this dichotomous problem, we introduce the degree of symmetry (DoS) as a non-negative continuous number ranging from zero to unity. DoS is defined through an average of the fidelity deviations of Hamiltonian or quantum state over its transformation group G, and thus is computable by making use of the completeness relations of the irreducible representations of G. The monotonicity of DoS can effectively probe the extended group for accidental degeneracy while its multi-valued natures characterize some (spontaneous) symmetry breaking.

quant-ph↗

arXiv2015

Graph states of prime-power dimension from generalized CNOT quantum circuit

We construct multipartite graph states whose dimension is the power of a prime number. This is realized by the finite field, as well as the generalized controlled-NOT quantum circuit acting on two qudits. We propose the standard form of graph states up to local unitary transformations and particle permutations. The form greatly simplifies the classification of graph states as we illustrate up to five qudits. We also show that some graph states are multipartite maximally entangled states in the sense that any bipartite of the system produces a bipartite maximally entangled state. We further prove that 4-partite maximally entangled states exist when the dimension is an odd number at least three or a multiple of four.

quant-ph↗

arXiv2015

Sudden transition from naked atom decay to dressed atom decay

The studies on quantum open system play key roles not only in fundamental problems in quantum mechanics but also in quantum computing and information processes. Here we propose a scheme to use a one dimensional coupling cavity array (CCA) as an artificial electromagnetic environment of a two-level atom. For a finite length of CCA, we find that after a turning time the population of excited state deviates suddenly from the exponential decay. We show that physically this phenomena corresponds to a transition from a naked atom decay to a dressed state decay. We hope that our finding will promote the studies on quantum system with a finite size environment.

quant-ph↗

arXiv2015

Turnplate of quantum state

Time-reversal symmetry breaking can enhance or suppress the probability of success for quantum state transfer (QST), and remarkably it can be used to implement the directional QST. In this paper we study the QST on a ring with time-reversal asymmetry. We show that the system will behave as a quantum state turnplate under some proper parameters, which may serve as time controlled quantum routers in complex quantum networks. We propose to to realize the quantum state turnplate in the coupled resonator optical waveguide by controlling the coupling strength and the phase.

quant-ph↗

arXiv2014

Multi-mode effects in cavity QED based on a one-dimensional cavity array

We present a microscopic mo del of cavity quantum electro dynamics based on a one-dimensional coupled cavity array (1D CCA), where a sup er cavity (SC) is comp osed by a segment of the 1D CCA with relatively smaller couplings with the outsides. The single-photon scattering problem for the SC empty or with a two-level atom is investigated. We obtain the exact theoretical result on the transmission rate for our system, which predicts the transmission p eaks shall app ear near the eigen-energies. Our numerical results further prove that the SC is a well-defined multi-mo de cavity. When a two-level atom resonant with the SC lo cates at the antino de of the resonant mo de, the transmission sp ectrum shows a clear sign of vacuum Rabi splitting as exp ected. However, when the atom lo cates at the no de of the resonant mo de, we observe a deep valley in the transmission p eak, which can b e explained by the destructive interference of two transmission channels, one is the resonant mo de, while the other is arising from the atom coupling with the non-resonance mo des. The effect of non-resonance mo des on vacuum Rabi splitting is also analyzed.

quant-ph↗

arXiv2014

Dissipation and decoherence induced by collective dephasing in coupled-qubit system with a common bath

The longitudinal coupling of a system to the bath usually induces the pure dephasing of the system. In this paper, we study the collective dephasing induced dissipation and decoherence in a coupled-qubit system with a common bath. It is shown that, compared with the case of the same system with independent baths, the interference between the dephasing processes of different qubits induced by the common bath significantly changes the dissipation of the system. For the system of two coupled qubits, the interference leads to a faster decoherence in the non-single-excitation subspaces and a slower dissipation (and decoherence) in the single-excitation subspace. For the system of multiple coupled qubits, we also find the slower dissipation in the single-excitation subspace and obtain the decay rates of the first excited states for different system sizes numerically. All our results on collective dephasing induced dissipation can be explained based on a simple model with Fermi's golden rule.

quant-ph↗

arXiv2014

Transfer arbitrary photon state along a cavity array without initialization

We propose a quantum state transfer (QST) scheme that transfers any single-mode photon state along a one-dimensional coupled-cavity array (CCA). By building a map from QST in a CCA to that in a spin-$\frac{1}{2}$ chain, we show that all the previous results of QST schemes for the spin chain system find paralleled applications in that in the CCA system. Further more, high fidelity QST along a long CCA can be achieved for arbitrary initial states. Using numerical simulations we provide a visual presentation of the result: at some time $τ$ the CCA system get high fidelity QST under different initial conditions. Finally we discuss possible experimental realizations of our QST scheme.

quant-ph↗

arXiv2014

Irreducible many-body correlations in topologically ordered systems

Topologically ordered systems exhibit large-scale correlation in their ground states, which may be characterized by quantities such as topological entanglement entropy. We propose that the concept of irreducible many-body correlation, the correlation that cannot be implied by all local correlations, may also be used as a signature of topological order. In a topologically ordered system, we demonstrate that for a part of the system with holes, the reduced density matrix exhibits irreducible many-body correlation which becomes reducible when the holes are removed. The appearance of these irreducible correlations then represents a key feature of topological phase. We analyze the many-body correlation structures in the ground state of the toric code model in an external magnetic field, and show that the topological phase transition is signaled by the irreducible many-body correlations.

quant-ph↗

arXiv2014

Optimized quantum state transfer through an XY spin chain

Quantum state transfer along a one-dimensional spin chain has become a fundamental ingredient for quantum communication between distant nodes in a quantum network. We study the average fidelity of quantum state transfer (QST) along a XY spin chain by adjusting the basis identification between the first spin and the last spin. In a proper choice of the basis identification, we find that the QST fidelity depends only on the average parity of the initial state linearly. We propose a simple scheme to adjusting the basis identification to optimize the average fidelity such that it depends linearly on the absolute value of the average parity. In the case that the absolute value of the average parity is $1$ we prove that the fidelity takes the maximum at any time over arbitrary initial state and basis identification.

quant-ph↗

arXiv2013

The quasi-dark state and quantum interference in Jaynes-Cummings model with a common bath

Within the capacity of current experiments, we design a composite atom-cavity system with a common bath, in which the decay channels of the atom and the cavity mode interfere with each other. When the direct atom-cavity coupling is absent, the system can be trapped in a quasi-dark state (the coherent superposition of excited states for the atom and the cavity mode) without decay even in the presence of the bath. When the atom directly couples with the cavity, the largest decay rate of the composite system will surpass the sum of the two subsystems while the smallest decay rate may achieve 0. This is manifested in the transmission spectrum, where the vacuum Rabi splitting shows an obvious asymmetric character.

quant-ph↗

arXiv2013

Non-Markovian dynamics in a spin star system: The failure of thermalization

In most cases, a small system weakly interacting with a thermal bath will finally reach the thermal state with the temperature of the bath. We show that this intuitive picture is not always true by a spin star model where non-Markov effect predominates in the whole dynamical process. The spin star system consists a central spin homogeneously interacting with an ensemble of identical noninteracting spins. We find that the correlation time of the bath is infinite, which implies that the bath has a perfect memory, and that the dynamical evolution of the central spin must be non- Markovian. A direct consequence is that the final state of the central spin is not the thermal state equilibrium with the bath, but a steady state which depends on its initial state.

quant-ph↗

arXiv2013

Super-additivity of quantum-correlating power

We prove that, when two local quantum channels are used paralleled, the quantum-correlating power (QCP) of the composed channel is no less than the sum of QCP of the two channels. For local channels with zero QCP, the super-activation of QCP is a fairly common effect, and proved to exist except for the trivial case where both of the channels are completely decohering channels or unitary operators. For general quantum channels, we show that the (not-so-common) additivity of QCP can be observed for the situation where a measuring-and-preparing channel is used together with a completely decohering channel.

quant-ph↗

arXiv2012

Optimal transfer of an unknown state via a bipartite operation

A fundamental task in quantum information science is to transfer an unknown state from particle $A$ to particle $B$ (often in remote space locations) by using a bipartite quantum operation $\mathcal{E}^{AB}$. We suggest the power of $\mathcal{E}^{AB}$ for quantum state transfer (QST) to be the maximal average probability of QST over the initial states of particle $B$ and the identifications of the state vectors between $A$ and $B$. We find the QST power of a bipartite quantum operations satisfies four desired properties between two $d$-dimensional Hilbert spaces. When $A$ and $B$ are qubits, the analytical expressions of the QST power is given. In particular, we obtain the exact results of the QST power for a general two-qubit unitary transformation.

quant-ph↗

arXiv2012

From Ground States to Local Hamiltonians

Traditional quantum physics solves ground states for a given Hamiltonian, while quantum information science asks for the existence and construction of certain Hamiltonians for given ground states. In practical situations, one would be mainly interested in local Hamiltonians with certain interaction patterns, such as nearest neighbour interactions on some type of lattices. A necessary condition for a space $V$ to be the ground-state space of some local Hamiltonian with a given interaction pattern, is that the maximally mixed state supported on $V$ is uniquely determined by its reduced density matrices associated with the given pattern, based on the principle of maximum entropy. However, it is unclear whether this condition is in general also sufficient. We examine the situations for the existence of such a local Hamiltonian to have $V$ satisfying the necessary condition mentioned above as its ground-state space, by linking to faces of the convex body of the local reduced states. We further discuss some methods for constructing the corresponding local Hamiltonians with given interaction patterns, mainly from physical points of view, including constructions related to perturbation methods, local frustration-free Hamiltonians, as well as thermodynamical ensembles.

quant-ph↗

arXiv2012

Quantum-correlating power of local quantum channels

Quantum correlation can be created by local operations from a classically correlated state. We define quantum-correlating power (QCP) of a local quantum channel as the maximum amount of quantum correlation that can be created by the channel. The quantum correlation that we discuss in this article is defined on the left part of the bipartite state. We prove that for any local channel, the optimal input state, which corresponds to the maximum quantum correlation in the output state, must be a classical-classical state. Further, the single-qubit channels with maximum QCP can be found in the class of rank-1 channels which take their optimal input states to rank-2 quantum-classical states. The analytic expression for QCP of single-qubit amplitude damping channel is obtained. Super-activation property of QCP, i.e., two zero-QCP channels can consist a positive-QCP channel, is discussed for single-qubit phase damping channels.

quant-ph↗

arXiv2012

Necessary and sufficient conditions for local creation of quantum correlation

Quantum correlation can be created by a local operation from some initially classical states. We prove that the necessary and sufficient condition for a local trace-preserving channel to create quantum correlation is that it is not a commutativity-preserving channel. This condition is valid for arbitrary finite dimension systems. We also derive the explicit form of commutativity-preserving channels. For a qubit, a commutativity-preserving channel is either a completely decohering channel or a mixing channel. For a three-dimensional system (qutrit), a commutativity-preserving channel is either a completely decohering channel or an isotropic channel.

quant-ph↗