arXiv subjects

Gui-Lu Long

Publications and source records attributed to Gui-Lu Long.

At least 91 records · Page 5Linked to original sources

arXiv2016

Minimum-Time Selective Control of Homonuclear Spins

In NMR (Nuclear Magnetic Resonance) quantum computation, the selective control of multiple homonuclear spins is usually slow because their resonance frequencies are very close to each other. To quickly implement controls against decoherence effects, this paper presents an efficient numerical algorithm fordesigning minimum-time local transformations in two homonuclear spins. We obtain an accurate minimum-time estimation via geometric analysis on the two-timescale decomposition of the dynamics. Such estimation narrows down the range of search for the minimum-time control with a gradient-type optimization algorithm. Numerical simulations show that this method can remarkably reduce the search efforts, especially when the frequency difference is very small and the control field is high. Its effectiveness is further demonstrated by NMR experiments with two homunuclear carbon spins in a trichloroethylene (C2H1Cl3) sample system.

quant-ph↗

arXiv2016

Sum uncertainty relations based on Wigner-Yanase skew information

We study sum uncertainty relations for arbitrary finite $N$ quantum mechanical observables. Some uncertainty inequalities are presented by using skew information introduced by Wigner and Yanase. These uncertainty inequalities are nontrivial as long as the observables are mutually noncommutative. The relations among these new and existing uncertainty inequalities have been investigated. Detailed examples are presented.

quant-ph↗

arXiv2015

Duality quantum computer and the efficient quantum simulations

In this paper, we firstly briefly review the duality quantum computer. Distinctly, the generalized quantum gates, the basic evolution operators in a duality quantum computer are no longer unitary, and they can be expressed in terms of linear combinations of unitary operators. All linear bounded operators can be realized in a duality quantum computer, and unitary operators are just the extreme points of the set of generalized quantum gates. A d-slits duality quantum computer can be realized in an ordinary quantum computer with an additional qudit using the duality quantum computing mode. Duality quantum computer provides flexibility and clear physical picture in designing quantum algorithms, serving as a useful bridge between quantum and classical algorithms. In this review, we will show that duality quantum computer can simulate quantum systems more efficiently than ordinary quantum computers by providing descriptions of the recent efficient quantum simulation algorithms of Childs et al [Quantum Information & Computation, 12(11-12): 901-924 (2012)] for the fast simulation of quantum systems with a sparse Hamiltonian, and the quantum simulation algorithm by Berry et al [Phys. Rev. Lett. 114, 090502 (2015)], which provides exponential improvement in precision for simulating systems with a sparse Hamiltonian.

quant-ph↗

arXiv2015

High-dimensional quantum state transfer in a noisy network environment

We propose and analyze an efficient high-dimensional quantum state transfer protocol in an XX coupling spin network with a hypercube structure or chain structure. Under free spin wave approximation, unitary evolution results in a perfect high-dimensional quantum swap operation requiring neither external manipulation nor weak coupling. Evolution time is independent of either distance between registers or dimensions of sent states, which can enable improvements in computational efficiency. In the low temperature regime and thermodynamic limit, the decoherence by noisy environment is studied with a model of an antiferromagnetic spin bath coupled to quantum channels via an Ising type interaction is studied. it is found that while the decoherence reduces the fidelity of state transfer, increasing intra-channel coupling can strongly suppress such effects. These observations demonstrate that robustness of the proposed scheme.

quant-ph↗

arXiv2014

Experimental entanglement-assisted quantum delayed-choice experiment

The puzzling properties of quantum mechanics, wave-particle duality, entanglement and superposition, were dissected experimentally at past decades. However, hidden-variable (HV) models, based on three classical assumptions of wave-particle objectivity, determinism and independence, strive to explain or even defeat them. The development of quantum technologies enabled us to test experimentally the predictions of quantum mechanics and HV theories. Here, we report an experimental demonstration of an entanglement-assisted quantum delayed-choice scheme using a liquid nuclear magnetic resonance quantum information processor. This scheme we realized is based on the recently proposed scheme [Nat. Comms. 5:4997(2014)], which gave different results for quantum mechanics and HV theories. In our experiments, the intensities and the visibilities of the interference are in consistent the theoretical prediction of quantum mechanics. The results imply that a contradiction is appearing when all three assumptions of HV models are combined, though any two of the above assumptions are compatible with it.

quant-ph↗

arXiv2014

Experimental Quantum Hamiltonian Identification from Measurement Time Traces

Identifying Hamiltonian of a quantum system is of vital importance for quantum information processing. In this Letter, we realized and benchmarked a quantum Hamiltonian identification algorithm recently proposed [Phys. Rev. Lett. \textbf{113}, 080401 (2014)]. we realized the algorithm on liquid nuclear magnetic resonance quantum information processor using two different working media with different forms of Hamiltonian. Our experiment realized the quantum identification algorithm based on free induction decay signals. We also showed how to process data obtained in practical experiment. We studied the influence of decoherence by numerical simulations. Our experiments and simulations demonstrate that the algorithm is effective and robust.

quant-ph↗

arXiv2014

Realistic Interpretation of Quantum Mechanics and Encounter-Delayed-Choice Experiment

A realistic interpretation(REIN) of wave function in quantum mechanics is briefly presented in this work. In REIN, the wave function of a microscopic object is just its real existence rather than a mere mathematical description. Quantum object can exist in disjoint regions of space which just as the wave function distributes, travels at a finite speed, and collapses instantly upon a measurement. The single photon interference in a Mach-Zehnder interferometer is analyzed using REIN. In particular, we proposed and experimentally implemented a generalized delayed-choice experiment, the encounter-delayed-choice(EDC) experiment, in which the second beam splitter is inserted at the encounter of the two sub-waves from the two arms. In the EDC experiment, the front parts of wave functions before the beam splitter insertion do not interfere and show the particle nature, and the back parts of the wave functions will interfere and show a wave nature. The predicted phenomenon is clearly demonstrated in the experiment, and supports the REIN idea.

quant-ph↗

arXiv2014

Superfluid density and Berezinskii-Kosterlitz-Thouless transition of a spin-orbit coupled Fulde-Ferrell superfluid

We theoretically investigate the superfluid density and Berezinskii-Kosterlitz-Thouless (BKT) transition of a two-dimensional Rashba spin-orbit coupled atomic Fermi gas with both in-plane and out-of-plane Zeeman fields. It was recently predicted that, by tuning the two Zeeman fields, the system may exhibit different exotic Fulde-Ferrell (FF) superfluid phases, including the gapped FF, gapless FF, gapless topological FF and gapped topological FF states. Due to the FF paring, we show that the superfluid density (tensor) of the system becomes anisotropic. When an in-plane Zeeman field is applied along the \textit{x}-direction, the tensor component along the \textit{y}-direction $n_{s,yy}$ is generally larger than $n_{s,xx}$ in most parameter space. At zero temperature, there is always a discontinuity jump in $n_{s,xx}$ as the system evolves from a gapped FF into a gapless FF state. With increasing temperature, such a jump is gradually washed out. The critical BKT temperature has been calculated as functions of the spin-orbit coupling strength, interatomic interaction strength, in-plane and out-of-plane Zeeman fields. We predict that the novel FF superfluid phases have a significant critical BKT temperature, typically at the order of $0.1T_{F}$, where $T_{F}$ is the Fermi degenerate temperature. Therefore, their observation is within the reach of current experimental techniques in cold-atom laboratories.

cond-mat.quant-gas↗

arXiv2014

Gapless topological Fulde-Ferrell superfluidity in spin-orbit coupled Fermi gases

Topological superfluids usually refer to a superfluid state which is gapped in the bulk but metallic at the boundary. Here we report that a gapless, topologically non-trivial superfluid with inhomogeneous Fulde-Ferrell pairing order parameter can emerge in a two-dimensional spin-orbit coupled Fermi gas, in the presence of both in-plane and out-of-plane Zeeman fields. The Fulde-Ferrell pairing - induced by the spin-orbit coupling and in-plane Zeeman field - is responsible for this gapless feature. This exotic superfluid has a significant Berezinskii-Kosterlitz-Thouless (BKT) transition temperature and has robust Majorana edge modes against disorder owing to its topological nature.

cond-mat.quant-gas↗

arXiv2014

Enhancement of quantum correlations between two particles under decoherence in finite temperature environment

Enhancing the quantum correlations in realistic quantum systems interacting with the environment of finite temperature is an important subject in quantum information processing. In this paper, we use weak measurement and measurement reversal to enhance the quantum correlations in a quantum system consisting of two particles. The transitions of the quantum correlations measured by the local quantum uncertainty of qubit-qubit and qutrit-qutrit quantum systems under generalized amplitude damping channels are investigated. We show that, after the weak measurement and measurement reversal, the joint system shows more robustness against decoherence.

quant-ph↗

arXiv2014

Band-selective shaped pulse for high fidelity quantum control in diamond

High fidelity quantum control over qubits is of crucial importance for realistic quantum computing, and it turns to be more challenging when there are inevitable interactions among qubits. By employing a bandselective shaped pulse, we demonstrate a high fidelity flip over electron spin of nitrogen-vacancy (NV) centers in diamond. In contrast with traditional rectangular pulses, the shaped pulse has almost equal excitation effect among a sharply edged region (in frequency domain). So the three sub-levels of host $^{14}N$ nuclear spin can be flipped accurately at the same time, while the redundant flip of other sublevels (e. g. of a nearby $^{13}C$ nuclear spin ) is well suppressed. The shaped pulse can be applied to a large amount of quantum systems in which band-selective operation are required.

quant-ph↗

arXiv2013

Entanglement classification of 2 X 2 X 2 X d quantum systems via the ranks of the multiple coefficient matrices

The coefficient matrix is an efficient tool in entanglement classification under stochastic local operation and classical communication. In this work, we take all the ranks of the coefficient matrices into account in the method of entanglement classification, and give the entanglement classification procedure for arbitrary-dimensional multipartite pure states under stochastic local operation and classical communication. As a main application, we study the entanglement classification for quantum systems in the Hilbert space ${\cal H} = \mathbb{C}^2 \otimes \mathbb{C}^2 \otimes \mathbb{C}^2 \otimes \mathbb{C}^d$ in terms of the ranks of the coefficient matrices.

quant-ph↗

arXiv2013

High-dimensional quantum state transfer through a quantum spin chain

In this paper, we investigate a high-dimensional quantum state transfer protocol. An arbitrary unknown high-dimensional state can be transferred with high fidelity between two remote registers through a XX coupling spin chain of arbitrary length. The evolution of the state transfer is determined by the natural dynamics of the chain without external modulation and coupling strength engineering. As a consequence, entanglement distribution with high efficiency can be achieved. Also the strong field and high spin quantum number can counteract partly the effect of finite temperature to ensure high fidelity of the protocol when the quantum data bus is in the thermal equilibrium state under an external magnetic field.

quant-ph↗

arXiv2013

Quantifying entanglement of arbitrary-dimensional multipartite pure states in terms of the singular values of coefficient matrices

The entanglement quantification and classification of multipartite quantum states are two important research fields in quantum information. In this work, we study the entanglement of arbitrary-dimensional multipartite pure states by looking at the averaged partial entropies of various bipartite partitions of the system, namely, the so-called Manhattan distance ($l_1$ norm) of averaged partial entropies (MAPE), and it is proved to be an entanglement measure for pure states. We connected the MAPE with the coefficient matrices, which are important tools in entanglement classification and reexpressed the MAPE for arbitrary-dimensional multipartite pure states by the nonzero singular values of the coefficient matrices. The entanglement properties of the $n$-qubit Dicke states, arbitrary-dimensional Greenberger-Horne-Zeilinger states, and $D_3^n$ states are investigated in terms of the MAPE, and the relation between the rank of the coefficient matrix and the degree of entanglement is demonstrated for symmetric states by two examples.

quant-ph↗

arXiv2011

Multipartite electronic entanglement purification with charge detection

We present a multipartite entanglement purification scheme in a Greenberger-Horne-Zeilinger state for electrons based on their spins and their charges. This scheme works for purification with two steps, i.e., bit-flipping error correction and phase-error flip error correction. By repeating these two steps, the parties in quantum communication can get some high-fidelity multipartite entangled electronic systems.

quant-ph↗

arXiv2009

Competition in rotation-alignment between high-j neutrons and protons in transfermium nuclei

The study of rotation-alignment of quasiparticles probes sensitively the properties of high-j intruder orbits. The distribution of very high-j orbits, which are consequences of the fundamental spin-orbit interaction, links with the important question of single-particle levels in superheavy nuclei. With the deformed single-particle states generated by the standard Nilsson potential, we perform Projected-Shell-Model calculations for transfermium nuclei where detailed spectroscopy experiment is currently possible. Specifically, we study the systematical behavior of rotation-alignment and associated band-crossing phenomenon in Cf, Fm, and No isotopes. Neutrons and protons from the high-j orbits are found to compete strongly in rotation-alignment, which gives rise to testable effects. Observation of these effects will provide direct information on the single-particle states in the heaviest nuclear mass region.

nucl-th↗

arXiv2008

gamma-vibrational states in superheavy nuclei

Recent experimental advances have made it possible to study excited structure in superheavy nuclei. The observed states have often been interpreted as quasi-particle excitations. We show that in superheavy nuclei collective vibrations systematically appear as low-energy excitation modes. By using the microscopic Triaxial Projected Shell Model, we make a detailed prediction on gamma-vibrational states and their E2 transition probabilities to the ground state band in Fermium and Nobelium isotopes where active structure research is going on, and in 270Ds, the heaviest isotope where decay data have been obtained for the ground-state and for an isomeric state.

nucl-th↗

arXiv2008

Coexistence of normal, super-, and hyper-deformation in nuclei: A study with angular momentum projection

Angular-momentum-projected energy surface calculations for A~110 nuclei indicate three distinct energy minima occurring at different angular-momenta. These correspond to normal, super-, and hyper-deformed shapes coexisting in one nucleus. 110Pd is studied in detail, with a quantitative prediction on super- and hyper-deformed spectra by the Projected Shell Model calculation. It is suggested that several other neighboring nuclei in the A-110 mass region, with the neutron number around 64, also exhibit clear super- and hyper-deformation minima.

nucl-th↗