Squeezed correlations of ϕ\phi meson pairs for hydrodynamic sources in high-energy heavy-ion collisions

In the hot and dense hadronic sources formed in high-energy heavy-ion collisions, the particle interactions in medium might lead to a squeezed back-to-back correlation (BBC) of boson-antiboson pairs. We calculate the BBC functions of $\phi\phi$ for sources evolving hydrodynamically in ($2+1$) dimensions and with longitudinal boost invariance. The BBC functions for hydrodynamic sources exhibit oscillations as a function of the particle momentum because the temporal distributions of hydrodynamic sources have sharp falls to 0 at large evolving times. The dependences of the BBC functions on the directions of the particle momentum are investigated. For transverse anisotropic sources, the BBC functions are minimum when the azimuthal angles of the particles reach 0. The BBC functions increase with decreasing absolute value of the particle pseudorapidity. The oscillations and the dependences on the particle azimuthal angle and pseudorapidity are the significant signatures for detecting the BBC in high-energy heavy-ion collisions.Comment: 17 pages, 10 figure

Back-to-back correlations of boson-antiboson pairs for anisotropic expanding sources

In the hot and dense hadronic sources formed in high energy heavy ion collisions, the particle interactions in medium might lead to a measurable back-to-back correlation (BBC) of boson-antiboson pairs. We calculate the BBC functions of $\phi\,\phi$ and $K^+K^-$ for anisotropic expanding sources. The dependences of the BBC on the particle momentum and source expanding velocity are investigated. The results indicate that the BBC functions increase with the magnitude of particle momentum and exhibit an obvious dependence on the direction of the momentum for the anisotropic sources. As the source expanding velocity decreases, the BBC function decreases when the particle momentum is approximately perpendicular to the source velocity, and the BBC function increases when the particle momentum is approximately parallel to the source velocity.Comment: 14 pages, 12 figures, a talk presented at the 2014 Autumn Conference of China Physical Society, Sep. 12-14, 2014, Harbin, Chin

Relaxation dynamics in an isolated long-range Ising chain

We consider a chain of trapped ions to interact with each other via long-range interactions. This system can be used to simulate the long-range Ising model. We study the dynamics of quantum coherence of a single spin in the chain, where the spins are initially prepared in their upper states. The relaxation dynamics exhibits due to the genuine long-range interaction. The degree of quantum coherence of a single spin rapidly decreases and vanishes in the steady state. However, our numerical result suggests that the conventional spin chain model, which truncates the interactions between the distant spins, cannot show the relaxation dynamics. This implies that the usual truncation in approximating the long-range interaction is not applicable to describing the non-equilibrium dynamics. The effect of the interaction range on the relaxation dynamics is studied. The higher relaxation rate will show if a system has a longer range of interaction. However, it takes a longer relaxation time in the vicinity of infinite interaction range. We also examine the dynamics of quantum coherence of a block of spins. Our result may shed light on the relationship between long-range interaction and the coherence dynamics of a quantum many-body system.Comment: 7 pages, 5 figure

Pion Transverse Momentum Spectrum, Elliptic Flow and Interferometry in the Granular Source Model in Ultra-Relativistic Heavy Ion Collisions

We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in the granular source model of quark-gluon plasma droplets in ultra-relativistic heavy ion collisions. The granular source model can well reproduce the experimental results of the Au-Au collisions at $\sqrt{s_{NN}}=$ 200 GeV and the Pb-Pb collisions at $\sqrt{s_{NN}} =$ 2.76 TeV with different centralities. We examine the parameters of the granular source models with an uniform and Woods-Saxon initial energy distributions in a droplet. The parameters exhibit certain regularities for collision centrality and energy.Comment: 10 pages, 3 figures, a talk at the Xth Workshop on Particle Correlations and Femtoscopy, Gyongyos Hungary, August 25-29, 201

Work Distributions in 1-D Fermions and Bosons with Dual Contact Interactions

We extend the well-known static duality \cite{girardeau1960relationship, cheon1999fermion} between 1-D Bosons and 1-D Fermions to the dynamical version. By utilizing this dynamical duality we find the duality of non-equilibrium work distributions between interacting 1-D bosonic (Lieb-Liniger model) and 1-D fermionic (Cheon-Shigehara model) systems with dual contact interactions. As a special case, the work distribution of the Tonks-Girardeau (TG) gas is identical to that of 1-D free fermionic system even though their momentum distributions are significantly different. In the classical limit, the work distributions of Lieb-Liniger models (Cheon-Shigehara models) with arbitrary coupling strength converge to that of the 1-D noninteracting distinguishable particles, although their elemetary excitations (quasi-particles) obey different statistics, e.g. the Bose-Einstein, the Fermi-Dirac and the fractional statistics. We also present numerical results of the work distributions of Lieb-Liniger model with various coupling strengths, which demonstrate the convergence of work distributions in the classical limit.Comment: 8 pages, 2 figure, 2 table

Quantum Implementation of Unitary Coupled Cluster for Simulating Molecular Electronic Structure

In classical computational chemistry, the coupled-cluster ansatz is one of the most commonly used $ab~initio$ methods, which is critically limited by its non-unitary nature. The unitary modification as an ideal solution to the problem is, however, extremely inefficient in classical conventional computation. Here, we provide the first experimental evidence that indeed the unitary version of the coupled cluster ansatz can be reliably performed in physical quantum system, a trapped ion system. We perform a simulation on the electronic structure of a molecular ion (HeH$^+$), where the ground-state energy surface curve is probed, energies of excited-states are studied and the bond-dissociation is simulated non-perturbatively. Our simulation takes advantages from quantum computation to overcome the intrinsic limitations in classical computation and our experimental results indicate that the method is promising for preparing molecular ground-states for quantum simulation.Comment: 6 pages, 4 figure

What retards the response of graphene based gaseous sensor

Graphene based sensor to gas molecules should be ultrasensitive and ultrafast because of the single-atomic thickness of graphene, while the response is not fast. Usually, the measured response time for many molecules, such as CO, NH3, SO2, CO2 and NO2 and so on, is on the scale of minutes or longer. In the present work, we found via \emph{ab initio} calculations there exists a potential barrier larger than 0.7 eV that hinders the gas molecule to land directly at the defective sites of graphene and retards the response. An efficient approach to the problem is suggested as modifying the graphene sheet with other molecules to reduce the potential barrier and was demonstrated by a graphene sheet modified by Fe2O3 molecules that shows fast response to H2S molecule, and the calculated response time is close to the measured one, 500 $\mu$s.Comment: 23 pages, 9 figure

Error-Mitigated Quantum Gates Exceeding Physical Fidelities in a Trapped-Ion System

Various quantum applications can be reduced to estimating expectation values, which are inevitably deviated by operational and environmental errors. Although errors can be tackled by quantum error correction, the overheads are far from being affordable for near-term technologies. To alleviate the detrimental effects of errors, quantum error mitigation techniques have been proposed, which require no additional qubit resources. Here, we benchmark the performance of a quantum error mitigation technique based on probabilistic error cancellation in a trapped-ion system. Our results clearly show that effective gate fidelities exceed physical fidelities, i.e. we surpass the break-even point of eliminating gate errors, by programming quantum circuits. The error rates are effectively reduced from $(1.10\pm 0.12)\times10^{-3}$ to $(1.44\pm 5.28)\times10^{-5}$ and from $(0.99\pm 0.06)\times10^{-2}$ to $(0.96\pm 0.10)\times10^{-3}$ for single- and two-qubit gates, respectively. Our demonstration opens up the possibility of implementing high-fidelity computations on a near-term noisy quantum device.Comment: 10 pages, 8 figure

Two-particle interferometry for the sources undergoing first-order QCD phase transition in high energy heavy ion collisions

We investigate the two-particle interferometry for the particle-emitting sources which undergo the first-order phase transition from the quark-gluon plasma with a finite baryon chemical potential to hadron resonance gas. The effects of source expansion, lifetime, and particle absorption on the transverse interferometry radii $R_{\rm out}$ and $R_{\rm side}$ are examined. We find that the emission durations of the particles become large when the system is initially located at the boundary between the mixed phase and the quark-gluon plasma. In this case, the difference between the radii $R_{\rm out}$ and $R_{\rm side}$ increases with the transverse momentum of the particle pair significantly. The ratio of $\sqrt{R_{\rm out}^2 -R_{\rm side}^2}$ to the transverse velocity of the pair is an observable for the enhancement of the emission duration.Comment: 10 pages, 12 figures. arXiv admin note: text overlap with arXiv:0811.475

Scalable global entangling gates on arbitrary ion qubits

A quantum algorithm can be decomposed into a sequence consisting of single qubit and 2-qubit entangling gates. To optimize the decomposition and achieve more efficient construction of the quantum circuit, we can replace multiple 2-qubit gates with a single global entangling gate. Here, we propose and implement a scalable scheme to realize the global entangling gates on multiple \yb ion qubits by coupling to multiple motional modes through external fields. Such global gates require simultaneously decoupling of multiple motional modes and balancing of the coupling strengths for all the qubit-pairs at the gate time. To satisfy the complicated requirements, we develop a trapped-ion system with fully-independent control capability on each ion, and experimentally realize the global entangling gates. As examples, we utilize them to prepare the Greenberger-Horne-Zeilinger (GHZ) states in a single entangling operation, and successfully show the genuine multi-partite entanglements up to four qubits with the state fidelities over $93.4\%$.Comment: Main: 7 pages, 4 figures and Methods: 4 pages, 2 figures and 2 table