Ion crystal transducer for strong coupling between single ions and single photons

A new approach for the realization of a quantum interface between single photons and single ions in an ion crystal is proposed and analyzed. In our approach the coupling between a single photon and a single ion is enhanced via the collective degrees of freedom of the ion crystal. Applications including single-photon generation, a memory for a quantum repeater, and a deterministic photon-photon, photon-phonon, or photon-ion entangler are discussed.     

Absorption of dislocation phonons by polarons at strong and weak coupling in alkali-halide crystals at low temperatures

It is shown that in alkali-halide crystals at low temperatures the deceleration of dislocations, whose high concentration may be caused by the internal photoeffect under illumination of the crystal by visible light, is influenced by their interaction with polarons. The deceleration force acting on a moving dislocation that interacts with polarons at not only strong but also weak coupling is calculated. Saratov State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 18–22, September 1999.     

Dephasing in quantum dots: quadratic coupling to acoustic phonons

A microscopic theory of optical transitions in quantum dots with a carrier-phonon interaction is developed. Virtual transitions into higher confined states with acoustic phonon assistance add a quadratic phonon coupling to the standard linear one, thus extending the independent boson model. Summing infinitely many diagrams in the cumulant, a numerically exact solution for the interband polarization is found. Its full time dependence and the absorption line shape of the quantum dot are calculated. It is the quadratic interaction which gives rise to a temperature-dependent broadening of the zero-phonon line, calculated here for the first time in a consistent scheme.     

Kinks and d-waves from phonons: The intermediate coupling story

I present results from an approach that extends the Eliashberg theory by systematic expansion in the vertex function; an essential extension at large phonon frequencies, even for weak coupling. In order to deal with computationally expensive double sums over momenta, a dynamical cluster approximation (DCA) approach is used to incorporate momentum dependence into the Eliashberg equations. First, I consider the effects of introducing partial momentum dependence on the standard Eliashberg theory using a quasi-local approximation; which I use to demonstrate that it is essential to include corrections beyond the standard theory when investigating d-wave states. Using the extended theory with vertex corrections, I compute electron and phonon spectral functions. A kink in the electronic dispersion is found in the normal state along the major symmetry directions, similar to that found in photo-emission from cuprates. The phonon spectral function shows that for weak coupling Wλ<ω₀, the dispersion for phonons has weak momentum dependence, with consequences for the theory of optical phonon mediated d-wave superconductivity, which is shown to be 2nd order in λ. In particular, examination of the order parameter vs. filling shows that vertex corrections lead to d-wave superconductivity mediated via simple optical phonons. I map out the order parameters in detail, showing that there is significant induced anisotropy in the superconducting pairing in quasi-2D systems.     

Quantum field theory for a system of interacting photons,electrons, and phonons

A Lagrangian in (1 + 3)-dimensional space-time which describes the interaction of photons, electrons, and phonons is proposed. This is a generalization of Rodriguez-Nuñez' model. This Lagrangian is also singular in the sense of Dirac. The path-integral quantization of this system is performed with the aid of the Dirac formalism for a singular Lagrangian and the method of functional integration. The phase-space generating functional of the Green function of this system is deduced. The Ward identities in canonical formalism for local symmetries are derived, and the Ward identities of proper vertices for this system are obtained. The conserved charges at the quantum level are also obtained. The effective Lagrangian in configuration space for the present model is derived in the case = const. Thus, the Feynman rule can be deduced immediately.     

基于操作腔外原子比特控制腔内原子比特相干性时间演化

考虑初始处于两类Bell态的两原子比特,将其中一个注入真空态腔中发生共振相互作用的情况,研究基于操作腔外原子比特控制腔内原子比特相干性时间演化.考察对腔外原子比特施Hadamard(H)门,H类门,Y门及位相门四种逻辑门操作及态选择测量前后,腔内原子比特约化密度矩阵非对角元时间演化曲线,讨论两类Bell态之间的关联性.结果表明,对腔外原子比特操作前,腔内原子比特密度矩阵非对角元在任意时刻都为零,总是处于混合态或经典态,因此始终退相干.而对腔外原子比特施H门和H类门操作及基态测量后,腔内原子比特密度矩阵非对角元呈现周期为2π的时间演化,除(2n+1)π/2时刻外,其相干性得到恢复;在nπ时刻,其最大相干叠加态和一般相干叠加态被制备;两类Bell态之间存在R∧(π/2)旋转关联性.而对腔外原子比特施Y门及位相门操作后,腔内原子比特的相干性得不到恢复.发现腔内原子比特的相干性得到恢复的必要条件是,逻辑门操作能够调节腔内原子比特与环境的相互作用,并使两原子比特与场分离的同时,它们之间形成强相干性的纠缠态分布.     

Coalescence of single photons emitted by disparate single-photon sources: the example of InAs quantum dots and parametric down-conversion sources

Single photons produced by fundamentally dissimilar physical processes will in general not be indistinguishable. We show how photons produced from a quantum dot and by parametric down-conversion in a nonlinear crystal can be manipulated to be indistinguishable. The measured two-photon coalescence probability is 16%, and is limited by quantum-dot decoherence. Temporal filtering to the quantum-dot coherence time and accounting for detector time response increases this to 61% while retaining 25% of the events. This technique can connect different elements in a scalable quantum network.     

Electron-phonon coupling and a polaron in the t-J model: from the weak to the strong coupling regime

We present numeric results for ground state and angle resolved photoemission spectra (ARPES) for a single hole in the t-J model coupled to optical phonons. The systematic-error-free diagrammatic Monte Carlo method is employed where the Feynman graphs for the Matsubara Green function in imaginary time are summed up completely with respect to phonon variables, while magnetic variables are subjected to the noncrossing approximation. We obtain that at electron-phonon coupling constants relevant for high T(c) cuprates the polaron undergoes a self-trapping crossover to the strong-coupling limit and theoretical ARPES demonstrate features observed in experiment: A broad peak in the bottom of the spectra has momentum dependence which coincides with that of a hole in the pure t-J model.     

通过光子与横向光频支声子直接耦合产生超声

详细地讨论了通过光子与横向光频支(TO)声子直接耦合产生高频超声问题。着重研究如下的原则性的实验方案:在构成共振腔主体的离子晶体中掺入某种活化原子(犹如固体激光器中受到抽运的杂质原子),其受激辐射的光能用于激发TO声子,从而获得超声振动向腔外的输出。分析的结果说明,为保证运行的稳定性,体现在声子与光子的非线性耦会以及声子间耦合的晶格振动非简谐性是必要的。对这种光一声装置的工作物质的探索。     

On S-transformation in the strong coupling theory

S-transformation is a unitary transformation accomplishing the main part of the diagonalization of the interaction Hamiltonian in strong coupling theories. For a compact symmetry group the action of the S-transformation on the integrals of motion is derived.Dedicated to Professor V. Votruba on his sixtieth birthday.     

Kinetic equations for electrons and phonons in a strong constant electric field

The kinetic equations for the electron and phonon distribution functions have been obtained for a system in an arbitrarily strong uniform constant electric field.     

Microcavity plasmonics: strong coupling of photonic cavities and plasmons

The understanding of light‐matter interactions at the nanoscale lays the groundwork for many future technologies, applications and materials. The scope of this article is the investigation of coupled photonic‐plasmonic systems consisting of a combination of photonic microcavities and metallic nanostructures. In such systems, it is possible to observe an exceptionally strong coupling between electromagnetic light modes of a resonator and collective electron oscillations (plasmons) in the metal. Furthermore, the results have shown that coupled photonic‐plasmonic structures possess a considerably higher sensitivity to changes in their environment than conventional localized plasmon sensors due to a plasmon excitation phase shift that depends on the environment.     

通过对腔外原子的操作控制腔内原子的发射性质

考虑初始处于纠缠态的三个双能级原子,将其中两个原子分别注入处于真空态的两个腔中,发生共振相互作用。通过对腔外原子进行操作,可使腔内两个原子的发射性质受到很大影响。