arXiv subjects

P. Zhang

Publications and source records attributed to P. Zhang.

196 records · Page 11Linked to original sources

arXiv2005

The pole structure of the unitary, crossing symmetric low energy $ππ$ scattering amplitudes

The pole structure of the low energy $ππ$ scattering amplitudes is studied using a proper chiral unitarization method combined with crossing symmetry and the low energy phase shift data. It is found that the $σ$ pole position is at $M_σ=470\pm 50MeV$, $Γ_σ=570\pm 50MeV$. The existence of the virtual state pole in the IJ=20 channel is reconfirmed. Various threshold parameters are estimated and are found in general in good agreement with the results obtained from the Roy equation analyses.

hep-ph↗

arXiv2005

The Sunyaev-Zeldovich effect in CMB-calibrated theories applied to the Cosmic Background Imager anisotropy power at l > 2000

We discuss the nature of the possible high-l excess in the Cosmic Microwave Background (CMB) anisotropy power spectrum observed by the Cosmic Background Imager (CBI). We probe the angular structure of the excess in the CBI deep fields and investigate whether it could be due to the scattering of CMB photons by hot electrons within clusters, the Sunyaev-Zeldovich (SZ) effect. We estimate the density fluctuation parameters for amplitude, sigma_8, and shape, Gamma, from CMB primary anisotropy data and other cosmological data. We use the results of two separate hydrodynamical codes for Lambda-CDM cosmologies, consistent with the allowed sigma_8 and Gamma values, to quantify the expected contribution from the SZ effect to the bandpowers of the CBI experiment and pass simulated SZ effect maps through our CBI analysis pipeline. The result is very sensitive to the value of sigma_8, and is roughly consistent with the observed power if sigma_8 ~ 1. We conclude that the CBI anomaly could be a result of the SZ effect for the class of Lambda-CDM concordance models if sigma_8 is in the upper range of values allowed by current CMB and Large Scale Structure (LSS) data.

astro-ph↗

arXiv2005

Effective boson-spin model for nuclei ensemble based universal quantum memory

We study the collective excitation of a macroscopic ensemble of polarized nuclei fixed in a quantum dot. Under the approximately homogeneous condition that we explicitly present in this paper, this many-particle system behaves as a single mode boson interacting with the spin of a single conduction band electron confined in this quantum dot. Within this effective spin-boson system, the quantum information carried by the electronic spin can be coherently transferred into the collective bosonic mode of excitation in the ensemble of nuclei. In this sense, the collective bosonic excitation can serve as a stable quantum memory to store the quantum information of spin state of electron.

quant-ph↗

arXiv2004

Holonomic Quantum Computation Using Rf-SQUIDs Coupled Through A Microwave Cavity

We propose a new scheme to realize holonomic quantum computation with rf-SQUID qubits in a microwave cavity. In this scheme associated with the non-Abelian holonomies, the single-qubit gates and a two-qubit control-Phase gate as well as a control-NOT gate can be easily constructed by tuning adiabatically the Rabi frequencies of classical microwave pulses coupled to the SQUIDs. The fidelity of these gates is estimated to be possibly higher than 90 % with the current technology.

quant-ph↗

arXiv2004

Creating Steady Atom-Molecule Entanglement by Demkov-Kunike Type Non-adiabatic Transition

We, based on the photoassociation of fermion atoms into bosonic molecules, propose a scheme to create the steady entanglement between the atom state and the molecule state inside an optical lattice. The stability of entanglement state is guaranteed by sweeping the frequency of Ramman laser beam through resonance according to the second Demkov-Kunike (DK2) nonadiabatic transition model\cite{DK,models}. The probability amplitude of each components can be precisely controlled by adjusting the sweeping parameter.

quant-ph↗

arXiv2004

Induced Magnetic Monopole from Trapped $Λ$-Type Atom

We investigate the spatial motion of the trapped atom with the electromagnetically induced transparency (EIT) configuration where the two Rabi transitions are coupled to two classical light fields respectively with the same detuning. When the internal degrees of freedom can be decoupled adiabatically from the spatial motion of the center of mass via the Born-Oppenheimer approximation, it is demonstrated that the lights of certain profile can provide the atom with an effective field of magnetic monopole, which is the so-called induced gauge field relevant to the Berry's phase. Such an artificial magnetic monopole structure manifests itself in the characterizing energy spectrum.

quant-ph↗

arXiv2004

Non-Abelian Geometric Quantum Memory with Atomic Ensemble

We study a quantum information storage scheme based on an atomic ensemble with near (also exact) three-photon resonance electromagnetically induced transparency (EIT). Each 4-level-atom is coupled to two classical control fields and a quantum probe field. Quantum information is adiabatically stored in the associated dark polariton manifold. An intrinsic non-trivial topological structure is discovered in our quantum memory implemented through the symmetric collective atomic excitations with a hidden SU(3) dynamical symmetry. By adiabatically changing the Rabi frequencies of two classical control fields, the quantum state can be retrieved up to a non-abelian holonomy and thus decoded from the final state in a purely geometric way.

quant-ph↗

arXiv2004

Two-Qubits Entanglement Induced by a Faster Data Bus

We propose a theoretical protocol to create the entanglement of two qubits via the Born-Oppenheimer (BO) approximation. In our scheme, each qubit is coupled to a faster data bus whose frequency is much larger than the energy spacing of the qubits and thus the BO approximation is valid. Then the adiabatic separation of qubits from the data bus can induce an effective potential to couple the two qubits, which can be utilized to create a quantum logic gate. We also discuss the quantum decoherence caused by the adiabatic entanglement between the two qubits and the external field.

quant-ph↗

arXiv2004

Fast entanglement of two charge-phase qubits through nonadiabatic coupling to a large junction

We propose a theoretical protocol for quantum logic gates between two Josephson junction charge-phase qubits through the control of their coupling to a large junction. In the low excitation limit of the large junction when $E_{J}\gg E_{c}$, it behaves effectively as a quantum data-bus mode of a harmonic oscillator. Our protocol is efficient and fast. In addition, it does not require the data-bus to stay adiabatically in its ground state, as such it can be implemented over a wide parameter regime independent of the data-bus quantum state.

cond-mat.supr-con↗

arXiv2004

Nonadiabatic effects of atomic motion inside a high Q optical cavity

We revisit the topic of atomic center of mass motion of a three level atom Raman coupled strongly to an external laser field and the quantum field of a high Q optical cavity. We focus on the motion related nonadiabatic effects of the atomic internal dynamics and provide a quantitative answer to the validity regime for the application of the motional insensitive dark state as recently suggested in Ref. [Phys. Rev. A {\bf 67}, 032305 (2003)].

quant-ph↗

arXiv2003

Geometric Quantum Information Storage Based on Atomic Ensemble

Quantum information storage (QIS) is a physical process to write quantum states into a quantum memory (QM). We observe that in some general cases the quantum state can be retrieved up to a unitary transformation depicted by the non-Abelian Berry's geometric phase factor (holonomy). The QIS of photon with this geometric character can be implemented with the symmetric collective excitations of a $Λ$-atom ensemble, which is adiabatically controlled by a classical light with a small detuning $δ$. The cyclic change of the controlled Rabi frequency $Ω(t)$ with period $T=\frac{2nπ}δ$ accumulates additional geometric phases in different components of the final photon state. Then, in a purely geometric way the stored state can be decoded from the final state.

quant-ph↗

arXiv2003

Two photon interference and optical free induction decay

The two photon interference phenomenon is theoretically investigated for the general situations with an arbitrary input two photon state with and without photon polarization. For the case without polarization, the necessary-sufficient condition for the destructive interference of coincidence counting is given as the symmetric pairing of photons in the light pulses. For both case it is shown that the "dip" in coincidence curve can be understood in terms of the free induction decay mechanism. This observation predicts the destructive interference phenomenon to occur even for certain cases with separable input two photon state, but it can only be explained in terms of "the two photon (not two photons)interference ".

quant-ph↗

arXiv2003

A criterion for testing multi-particle NPT entanglement

We revisit the criterion of multi-particle entanglement based on the overlaps of a given quantum state $ρ$ with maximally entangled states. For a system of $m$ particles, each with $N$ distinct states, we prove that $ρ$ is $m$-particle negative partial transpose (NPT) entangled, if there exists a maximally entangled state $|{\rm MES}>$, such that $<{\rm MES}|ρ|{\rm MES}>>{1}/{N}$. While this sufficiency condition is weaker than the Peres-Horodecki criterion in all cases, it applies to multi-particle systems, and becomes especially useful when the number of particles ($m$) is large. We also consider the converse of this criterion and illustrate its invalidity with counter examples.

quant-ph↗

arXiv2003

Superradiance of low density Frenkel excitons in a crystal slab of three-level atoms: Quantum interference effect

We systematically study the fluorescence of low density Frenkel excitons in a crystal slab containing $N_T$ V-type three-level atoms. Based on symmetric quasi-spin realization of SU(3) in large $N$ limit, the two-mode exciton operators are invoked to depict various collective excitations of the collection of these V-type atoms starting from their ground state. By making use of the rotating wave approximation, the light intensity of radiation for the single lattice layer is investigated in detail. As a quantum coherence effect, the quantum beat phenomenon is discussed in detail for different initial excitonic states. We also test the above results analytically without the consideration of the rotating wave approximation and the self-interaction of radiance field is also included.

cond-mat↗

arXiv2002

An quantum approach of measurement based on the Zurek's triple model

In a close form without referring the time-dependent Hamiltonian to the total system, a consistent approach for quantum measurement is proposed based on Zurek's triple model of quantum decoherence [W.Zurek, Phys. Rev. D 24, 1516 (1981)]. An exactly-solvable model based on the intracavity system is dealt with in details to demonstrate the central idea in our approach: by peeling off one collective variable of the measuring apparatus from its many degrees of freedom, as the pointer of the apparatus, the collective variable de-couples with the internal environment formed by the effective internal variables, but still interacts with the measured system to form a triple entanglement among the measured system, the pointer and the internal environment. As another mechanism to cause decoherence, the uncertainty of relative phase and its many-particle amplification can be summed up to an ideal entanglement or an Shmidt decomposition with respect to the preferred basis.

quant-ph↗

arXiv2001

High order quantum decoherence via multi-particle amplitude for boson system

In this paper we depict the high order quantum coherence of a boson system by using the multi-particle wave amplitude, whose norm square is just the high order correlation function. This multi-time amplitude can be shown to be a superposition of several "multi-particle paths". When the environment or a apparatus entangles with them to form a generalized "which-way" measurement for many particle system, the quantum decoherence happens in the high order case dynamically. An explicit illustration is also given with an intracavity system of two modes interacting with a moving mirror.

quant-ph↗