QED Interaction Research Articles

Heralded multiphoton states with coherent spin interactions in waveguide QED

Waveguide QED offers the possibility of generating strong coherent atomic interactions either through appropriate atomic configurations in the dissipative regime or in the bandgap regime. In this work, we show how to harness these interactions in order to herald the generation of highly entangled atomic states, which afterwards can be mapped to generate single mode multi-photonic states with high fidelities. We introduce two protocols for the preparation of the atomic states, we discuss their performance and compare them to previous proposals. In particular, we show that one of them reaches high probability of success for systems with many atoms but low Purcell factors.

Polarization of a probe laser beam due to nonlinear QED effects

Nonlinear QED interactions induce different polarization properties on a given probe beam. We consider the polarization effects caused by the photon-photon interaction in laser experiments, when a laser beam propagates through a constant magnetic field or collides with another laser beam. We solve the quantum Boltzmann equation within the framework of the Euler-Heisenberg Lagrangian for both time-dependent and constant background field to explore the time evolution of the Stokes parameters Q, U, and V describing polarization. Assuming an initially linearly polarized probe laser beam, we also calculate the induced ellipticity and rotation of the polarization plane.

Dressed Photons Induced Resistance Oscillation and Zero Resistance in Arrayed Simple Harmonic Oscillators with No Impurity.

We investigate a system of an array of N simple harmonic oscillators (SHO) interacting with photons through QED interaction. As the energy of photon is around the spacing between SHO energy levels, energy gaps appear in the dispersion relation of the interacted (dressed) photons. This is quite different from the dispersion relation of free photons. Due to interactions between dressed photonic field and arrayed SHO, the photoresistance of this system shows oscillations and also drops to zero as irradiated by EM field of varying frequencies.

Gauge symmetries emerging from extra dimensions

We argue that extra dimensions with a properly chosen compactification scheme could be a natural source for emergent gauge symmetries. Actually, some proposed vector field potential terms or polynomial vector field constraints introduced in five-dimensional Abelian and non-Abelian gauge theory is shown to smoothly lead to spontaneous violation of an underlying 5D spacetime symmetry and generate pseudo-Goldstone vector modes as conventional 4D gauge boson candidates. As a special signature, there appear, apart from conventional gauge couplings, some properly suppressed direct multi-photon (multi-boson, in general) interactions in emergent QED and Yang-Mills theories whose observation could shed light on their high-dimensional nature. Moreover, in emergent Yang-Mills theories an internal symmetry G also occurs spontaneously broken to its diagonal subgroups once 5D Lorentz violation happens. This breaking origins from the extra vector field components playing a role of some adjoint scalar field multiplet in the 4D spacetime. So, one naturally has the Higgs effect without a specially introduced scalar field multiplet. Remarkably, when being applied to Grand Unified Theories this results in a fact that the emergent GUTs generically appear broken down to the Standard Model just at the 5D Lorentz violation scale M. PACS numbers: 11.15.-q, 11.30.Cp, 11.30.Pb, 11.10.Kk

Noise Effects on Entangled Coherent State Generated via Atom-Field Interaction and Beam Splitter

In this paper, we introduce a controllable method for producing two and three-mode entangled coherent states (ECS's) using atom-field interaction in cavity QED and beam splitter. The generated states play central roles in linear optics, quantum computation and teleportation. We especially focus on qubit, qutrit and qufit like ECS's and investigate their entanglement by concurrence measure. Moreover, we illustrate decoherence properties of ECS's due to noisy channels, using negativity measure. At the end the effect of noise on monogamy inequality is discussed.

Chiral asymmetry in cold QED plasma in a strong magnetic field

The interaction induced chiral asymmetry is calculated in cold QED plasma beyond the weak-field approximation. By making use of the recently developed Landau-level representation for the fermion self-energy, the chiral shift and the parity-even chiral chemical potential function are obtained with the help of numerical methods. The results are used to quantify the chiral asymmetry of the Fermi surface in dense QED matter. Because of the weakness of the QED interactions, the value of the asymmetry appears to be rather small even in the strongest magnetic fields and at the highest stellar densities. However, the analogous asymmetry can be substantial in the case of dense quark matter.

The CTA sensitivity to Lorentz-violating effects on the gamma-ray horizon

The arrival of TeV-energy photons from distant galaxies isexpected to be affected by their QED interaction with intergalactic radiation fieldsthrough electron-positron pair production. In theories where high-energy photons violate Lorentz symmetry,the kinematics of the process γ+γ→e++e− is altered and the cross section suppressed.Consequently, one would expect more of the highest-energy photons to arrive if QED is modified by Lorentz violation than if it is not.We estimate the sensitivity of Cherenkov Telescope Array (CTA) to changes in the gamma-ray horizonof the Universe due to Lorentz violation, and find that it should be competitive with other leading constraints.

Quantum phases in circuit QED with a superconducting qubit array

Circuit QED on a chip has become a powerful platform for simulating complex many-body physics. In this report, we realize a Dicke-Ising model with an antiferromagnetic nearest-neighbor spin-spin interaction in circuit QED with a superconducting qubit array. We show that this system exhibits a competition between the collective spin-photon interaction and the antiferromagnetic nearest-neighbor spin-spin interaction, and then predict four quantum phases, including: a paramagnetic normal phase, an antiferromagnetic normal phase, a paramagnetic superradiant phase, and an antiferromagnetic superradiant phase. The antiferromagnetic normal phase and the antiferromagnetic superradiant phase are new phases in many-body quantum optics. In the antiferromagnetic superradiant phase, both the antiferromagnetic and superradiant orders can coexist, and thus the system possesses symmetry. Moreover, we find an unconventional photon signature in this phase. In future experiments, these predicted quantum phases could be distinguished by detecting both the mean-photon number and the magnetization.

Pair creation by collision of an intense laser pulse with a high-frequency photon beam

We consider pair creation by collision of a couple of counterpropagating electromagnetic pulses with arbitrary frequency ratio, mostly in the context of setup with collision of optical and coherent hard X- (or gamma-) ray pulses. This problem is non-perturbative and in general does not admit exact analytical solutions. We discuss several known approaches according to the ratio of the parameters. Certain regions of the parameter space are not covered by the existing approximations or models. We present a new simplified exactly solvable model with one of the pulses being a delta-pulse. This model partially fills the yet unexplored gap in the space of parameters. The shape of the momentum distribution of the created particles in such a model is discussed. Even though the model may not have immediate implications for the forthcoming experiments, it can still provide some hints for better understanding of the fully non-perturbative regime and vacuum instability in QED interactions of extremely strong and short laser pulses.

Proposal for a loophole-free Bell test based on spin–photon interactions in cavities

We present a scheme to demonstrate loophole-free Bell inequality violation where the entanglement between photon pairs is transferred to solid state (spin) qubits mediated by cavity QED interactions. As this transfer can be achieved in a heralded way, our scheme is basically insensitive to losses on the channel, and works also in the weak coupling regime. We consider potential experimental realizations using single atom, colour centre and quantum dot cavity systems. Finally our scheme appears to be promising for implementing quantum information protocols based on non-locality. Here we discuss a possible implementation of device-independent quantum key distribution.

Chiral asymmetry in QED matter in a magnetic field

We calculate the electron self-energy in a magnetized QED plasma to the leading perturbative order in the coupling constant and to the linear order in an external magnetic field. We find that the chiral asymmetry of the normal ground state of the system is characterized by two new Dirac structures. One of them is the familiar chiral shift previously discussed in the Nambu--Jona-Lasinio model. The other structure is new. It formally looks like that of the chiral chemical potential but is an odd function of the longitudinal component of the momentum, directed along the magnetic field. The origin of this new parity-even chiral structure is directly connected with the long-range character of the QED interaction. The form of the Fermi surface in the weak magnetic field is determined.

Leading isospin breaking effects on the lattice

We present a method to evaluate on the lattice the leading isospin breaking effects due to both the small mass difference between the up and down quarks and the QED interaction. Our proposal is applicable in principle to any QCD+QED gauge invariant hadronic observable which can be computed on the lattice. It is based on the expansion of the path-integral in powers of the small parameters (m_d - m_u)/Lambda_{QCD} and alpha_{em}, where m_f is the renormalized quark mass and alpha_{em} the renormalized fine structure constant. In this paper we discuss in detail the general strategy of the method and the conventional, although arbitrary, separation of QCD from QED isospin breaking corrections. We obtain results for the pion mass splitting, M_{pi+}^2-M_{pi0}^2= 1.44(13)(16) x 10^3 MeV^2, for the Dashen's theorem breaking parameter epsilon_{gamma}= 0.79(18)(18), for the light quark masses, [m_d - m_u](MSbar,2 GeV)= 2.39(8)(17) MeV, [m_u / m_d](MSbar,2 GeV)= 0.50(2)(3) and for the flavour symmetry breaking parameters R and Q. We also update our previous results for the QCD isospin breaking corrections to the Kl2 decay rate and for the QCD contribution to the neutron-proton mass splitting.

Implementation of Toffoli gates with a single asymmetric HeisenbergXYinteraction

The Toffoli gate, which has practical applications in the implementation of practical quantum algorithms and quantum error correction, is usually constructed from concatenated two-qubit or qubit-qutrit gates. Here we show that the Toffoli gate for three qubits can be implemented through a single $\mathit{XY}$ interaction plus two single-qubit rotations. This method greatly simplifies the experimental implementation of the Toffoli gate and promises a much higher fidelity compared to those based on elementary gate decomposition. We present an example for the implementation of the required $\mathit{XY}$ interaction in cavity QED.

Phase space evolution of pairs created in strong electric fields

We study the process of energy conversion from overcritical electric field into electron–positron–photon plasma. We solve numerically Vlasov–Boltzmann equations for pairs and photons assuming the system to be homogeneous and anisotropic. All the 2-particle QED interactions between pairs and photons are described by collision terms. We evidence several epochs of this energy conversion, each of them associated to a specific physical process. Firstly pair creation occurs, secondly back reaction results in plasma oscillations. Thirdly photons are produced by electron–positron annihilation. Finally particle interactions lead to completely equilibrated thermal electron–positron–photon plasma.

Scheme for generation of four-atom Greenberger–Horne–Zeilinger states in an optical cavity

We propose a scheme for generating maximally GHZ state for four atoms trapped in a two-mode optical cavity via combination of cavity QED and linear optics system. The GHZ state can be not only generated deterministically with a single resonant interaction in cavity QED, but also can be prepared probabilistically based on cavity QED and linear optics elements. The fidelity of the entangled states is not affected by the atomic spontaneous, cavity decay, and imperfection of the photon-detectors. Finally, we briefly analyze and discuss the experimental feasibility of the proposed scheme.

Electromagnetic mass splittings of the low lying hadrons and quark masses from2+1flavor latticeQCD+QED

Results computed in lattice $\mathrm{QCD}+\mathrm{QED}$ are presented for the electromagnetic mass splittings of the low-lying hadrons. These are used to determine the renormalized, nondegenerate, light quark masses. It is found that ${m}_{u}^{\overline{\mathrm{MS}}}=2.24(10)(34)$, ${m}_{d}^{\overline{\mathrm{MS}}}=4.65(15)(32)$, and ${m}_{s}^{\overline{\mathrm{MS}}}=97.6(2.9)(5.5)\text{ }\text{ }\mathrm{MeV}$ at the renormalization scale 2 GeV, where the first error is statistical and the second systematic. We find the lowest-order electromagnetic splitting $({m}_{{\ensuremath{\pi}}^{+}}\ensuremath{-}{m}_{{\ensuremath{\pi}}^{0}}{)}_{\mathrm{QED}}=3.38(23)\text{ }\text{ }\mathrm{MeV}$, the splittings including next-to-leading order, $({m}_{{\ensuremath{\pi}}^{+}}\ensuremath{-}{m}_{{\ensuremath{\pi}}^{0}}{)}_{\mathrm{QED}}=4.50(23)\text{ }\text{ }\mathrm{MeV}$, $({m}_{{K}^{+}}\ensuremath{-}{m}_{{K}^{0}}{)}_{\mathrm{QED}}=1.87(10)\text{ }\text{ }\mathrm{MeV}$, and the ${m}_{u}\ensuremath{\ne}{m}_{d}$ contribution to the kaon mass difference, $({m}_{{K}^{+}}\ensuremath{-}{m}_{{K}^{0}}{)}_{({m}_{u}\ensuremath{-}{m}_{d})}=\ensuremath{-}5.840(96)\text{ }\text{ }\mathrm{MeV}$. All errors are statistical only, and the next-to-leading-order pion splitting is only approximate in that it does not contain all next-to-leading-order contributions. We also computed the proton-neutron mass difference, including for the first time, QED interactions in a realistic $2+1$ flavor calculation. We find $({m}_{p}\ensuremath{-}{m}_{n}{)}_{\mathrm{QED}}=0.383(68)\text{ }\text{ }\mathrm{MeV}$, $({m}_{p}\ensuremath{-}{m}_{n}{)}_{({m}_{u}\ensuremath{-}{m}_{d})}=\ensuremath{-}2.51(14)\text{ }\text{ }\mathrm{MeV}$ (statistical errors only), and the total ${m}_{p}\ensuremath{-}{m}_{n}=\ensuremath{-}2.13(16)(70)\text{ }\text{ }\mathrm{MeV}$, where the first error is statistical, and the second, part of the systematic error. The calculations are carried out on QCD ensembles generated by the RBC and UKQCD collaborations, using domain wall fermions and the Iwasaki gauge action (gauge coupling $\ensuremath{\beta}=2.13$ and lattice cutoff ${a}^{\ensuremath{-}1}\ensuremath{\approx}1.78\text{ }\text{ }\mathrm{GeV}$). We use two lattice sizes, ${16}^{3}$ and ${24}^{3}$ ($(1.8\text{ }\text{ }\mathrm{fm}{)}^{3}$ and $(2.7\text{ }\text{ }\mathrm{fm}{)}^{3}$), to address finite-volume effects. Noncompact QED is treated in the quenched approximation. The valence pseudoscalar meson masses in our study cover a range of about 250 to 700 MeV, though we use only those up to about 400 MeV to quote final results. We present new results for the electromagnetic low-energy constants in SU(3) and SU(2) partially quenched chiral perturbation theory to the next-to-leading order, obtained from fits to our data. Detailed analysis of systematic errors in our results and methods for improving them are discussed. Finally, new analytic results for $\mathrm{SU}(2{)}_{\mathrm{L}}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2{)}_{\mathrm{R}}$-plus-kaon chiral perturbation theory, including the one-loop logs proportional to ${\ensuremath{\alpha}}_{\mathrm{em}}m$, are given.

Teleportation of N-qubit W State without Bell-State Measurement via Selective Resonant Interaction in Cavity QED

We present a scheme in which the N-atom W state is teleported by employing the selective interaction of a cavity field with a driven three-level atom in the A configuration and detecting a single atom in one of the ground states. The long-lived W state is teleported from atom A to atom B when the atoms B and A are sent through a cavity successively and atom A is then detected. The advantage is that the present one does not involve the Bell-state measurement and is robust against the atomic spontaneous emission.

Additional requirements for consistent description of nonlocal interactions in QED

This paper is devoted to the study of the combined description of local and nonlocal matter fields in the framework of quantum electrodynamics. Additionally considering the properties of inseparability of the ideas of charge and mass for fundamental particles and the indifference of electromagnetic forces to structure-forming interactions, which had a hidden character in the local theory, provided the conservation in the unchanged form of the group of local gauge symmetries and the correct transition beyond the framework of the local theory. The structural limit of local consideration, which does not violate the results previously obtained in the framework of the local theory, is studied. The general properties of the regular part of the generalized pole amplitude are discussed.

Physical qubits from charged particles: Infrared divergences in quantum information

We consider soft-photon effects (ir structure of QED) on the construction of physical qubits. Soft photons appear when we build charged qubits from the asymptotic states of QED. This construction is necessary in order to include the effect of soft photons on entanglement measures. The nonexistence of free charged particles (due to the long range of QED interactions) leads us to question the sense of the very concept of free charged qubit. In this work, using the ``dressing'' formalism, we build physical charged qubits from dressed fields which have the correct asymptotic behavior, are gauge invariant, have propagators with a particle pole structure, and are free from infrared divergences. Finally, we discuss the impact of the soft corrections on the entanglement measures.

Temperature dependence of violation of Bell’s inequality in coupled quantum dots in a microcavity

Bell's inequality in two coupled quantum dots within cavity QED, including Forster and exciton-phonon interactions, is investigated theoretically. It is shown that the environmental temperature has a significant impact on Bell's inequality.