QED Photon Research Articles

Low-energy limit of N-photon amplitudes in a constant field

While the QED photon amplitudes at full momentum so far have been calculated only up to the six-photon level, in the low-energy limit there are explicit formulas for all helicity components even at the N-photon level, obtained by Martin et al. in 2002. Here we use the worldline formalism to extend that result to the N-photon amplitudes in a generic constant field. For both scalar and spinor QED, we obtain compact representations for the low-energy limits of these amplitudes involving only simple algebra and a single global proper-time integral with trigonometric integrand.

Challenges with internal photons in constructive QED

We find the correct spinor amplitude for a simple photon-mediated process and show that, in contrast, the result for the same process using the standard constructive techniques do not agree with Feynman diagrams when the fermions are massive. Along the way, we analyze the x factor used in photon vertices, we work out the spinor shifts for massive particles when the momenta are analytically continued and we consider the large z limit of the amplitudes in this paper and show that the photon-mediated process does not vanish in this limit for any choice of two of its momenta. For comparison with the photon-mediated process, we also describe two processes with external photons that are mediated by massive particles. In both cases, we show that the current techniques are sufficient and that the final results agree with Feynman diagrams. We also demonstrate that by using a massive photon in our calculations and taking the massless limit at the end, we can achieve agreement with Feynman diagrams in all the processes discussed here, including the photon-mediated amplitudes.

Self-ordering of individual photons in waveguide QED and Rydberg-atom arrays

The scattering between light and individual saturable quantum emitters can induce strong optical nonlinearities and correlations between individual light quanta. Typically, this leads to an effective attraction that can generate exotic bound states of photons, which form quantum mechanical precursors of optical solitons, as found in many optical media. Here, we study the propagation of light through an optical waveguide that is chirally coupled to three-level quantum emitters. We show that the additional laser-coupling to a third emitter state not only permits to control the properties of the bound state but can even eliminate it entirely. This makes it possible to turn an otherwise focussing nonlinearity into a repulsive photon-photon interaction. We demonstrate this emerging photon-photon repulsion by analysing the quantum dynamics of multiple photons in large emitter arrays and reveal a dynamical fragmentation of incident uncorrelated light fields and self-ordering into regular trains of single photons. These striking effects expand the rich physics of waveguide quantum electrodynamics into the domain of repulsive photons and establish a conceptually simple platform to explore optical self-organization phenomena at the quantum level. We discuss implementations of this setting in cold-atom experiments and propose a new approach based on arrays of mesoscopic Rydberg-atom ensembles.

Gauge kinetic mixing and dark topological defects

We discuss how the topological defects in the dark sector affect the Standard Model sector when the dark photon has a kinetic mixing with the QED photon. In particular, we consider the dark photon appearing in the successive gauge symmetry breaking, SU(2) → U(1) → ℤ2, where the remaining ℤ2 is the center of SU(2). In this model, the monopole is trapped into the cosmic strings and forms the so-called bead solution. As we will discuss, the dark cosmic string induces the QED magnetic flux inside the dark string through the kinetic mixing. The dark monopole, on the other hand, does not induce the QED magnetic flux in the U(1) symmetric phase, even in the presence of the kinetic mixing. Finally, we show that the dark bead solution induces a spherically symmetric QED magnetic flux through the kinetic mixing. The induced flux looks like the QED magnetic monopole viewed from a distance, although QED satisfies the Bianchi identity everywhere, which we call a pseudo magnetic monopole.

Counting statistics of microwave photons in circuit QED

In superconducting circuit architectures for quantum computing, microwave resonators are often used both to isolate qubits from the electromagnetic environment and to facilitate qubit state readout. We analyze the full counting statistics of photons emitted from such driven readout resonators both in and beyond the dispersive approximation. We calculate the overlap between emitted-photon distributions for the two qubit states and explore strategies for its minimization with the purpose of increasing fidelity of intensity-sensitive readout techniques. In the dispersive approximation and at negligible qubit relaxation, both distributions are Poissonian, and the overlap between them can be easily made arbitrarily small. Nondispersive terms of the Hamiltonian generate squeezing and the Purcell decay with the latter effect giving the dominant contribution to the overlap between two distributions.

Loop corrected soft photon theorem as a Ward identity

Recently Sahoo and Sen obtained a series of remarkable results concerning sub­ leading soft photon and graviton theorems in four dimensions. Even though the S-matrix is infrared divergent, they have shown that the subleading soft theorems are well defined and exact statements in QED and perturbative Quantum Gravity. However unlike the well studied Cachazo-Strominger soft theorems in tree-level amplitudes, the new subleading soft expansion is at the order ln w (where w is the soft frequency) and the corresponding soft factors structurally show completely different properties then their tree-level counterparts. Whence it is natural to ask if these theorems are associated to asymptotic symmetries of the S-matrix.We consider this question in the context of sub-leading soft photon theorem in scalar QED and show that there are indeed an infinity of conservation laws whose Ward identities are equivalent to the loop-corrected soft photon theorem. This shows that in the case of four dimensional QED, the leading and sub-leading soft photon theorems are equivalent to Ward identities of (asymptotic) charges.

Creating lattice gauge potentials in circuit QED: The bosonic Creutz ladder

In this work we propose two protocols to make an effective gauge potential for microwave photons in circuit QED. The schemes consist of coupled transmons whose flux are harmonically modulated in time. We investigate the effect of various types of capacitive and inductive couplings, and the role of the fixed phase offset of each site on the complex coupling rate between coupled qubits. These configurations can be directly realised in a superconducting circuit and is easily extendable to a scalable lattice. Due to the intrinsic non-linearity of the transmon qubits such lattices would be an ideal platform for simulating Bose-Hubbard Hamiltonians with non-trivial gauge fields.

Preface

PREFACEThe “Victor Villanueva Memorial Meeting” to pay homage to our friend and colleague Victor Manuel Villanueva Sandoval was held at the premises of the Institute of Physics and Mathematics, University of Michoacán in Morelia, Michoacán, Mexico, on December 6, 2013, about 3 months after his tragic demise. This gathering was attended by his close friends, family, collaborators, colleagues and students. Several of those who could not physically be present for this commemorative gathering sent their messages of condolence and/or scientific contributions for this proceedings volume for which we are immensely grateful.The meeting started with personal recollections by Victor’s wife Ana Rosa Tenorio Lúa and his sisters Alejandra and Gabriela Villanueva. His daughters Ana Paola, Daniela and Mariana were also present to grace the solemn occasion and later provided us with their heart-felt messages. The academic part of the meeting started with Adnan Bashir presenting a summary of Victor’s scientific life, his research and its impact.Research talks were then presented by Luis Villaseñor (Ultra energetic cosmic rays - recent results), Mauro Napsuciale (A formalism for higher spins based on parity), Christian Schubert (Amplitudes with many photons in QED), Naser Ahmadiniaz (Amplitudes with gluons in a string inspired formalism), Carlos Vaquera (Second order fermions and renormalization) and Adnan Bashir (Strong interactions - peculiarities and challenges). There were several potential and interested speakers who were unable to physically attend the meeting but, as we have mentioned before, agreed to send their contribution for the proceedings volume at a later date. They are Dmitry Antonov (University of Lisboa, Portugal), Fiorenzo Bastianelli and Roberto Bonezzi (University of Bologna and INFN, Italy), Olindo Corradini (University of Modena and Reggio Emilia, Italy), Pietro Dall’Olio (University of Michoacán, Mexico), Jan Govaerts (Université Catholique de Louvian, Belgium), Emanuele Latini (University of Zurich, Switzerland), Khaled Hassan Ould-Lahoucie (University Ferhat Abbas of Setif, Algeria), Eckehard Mielke (Metropolitan Autonomous University of Iztapalapa, Mexico), Néstor Ortiz, Olivier Sarbach and Thomas Zannias (University of Michoacán, Mexico).We are very grateful to the director Ricardo Becerril and personnel of the Institute of Physics and Mathematics, University of Michoacán, who ensured a smooth and pleasant organization of the meeting. We offer our special thanks to Itzel Alvarez who prepared a beautiful poster to announce the meeting. She also organized the personal part of the material for the proceedings in an outstanding manner.Finally, we would like this meeting and the proceedings volume to serve as a token of our appreciation and admiration for our friend Victor Villanueva. We also hope it serves as an inspiration for Victor’s students and his daughters Paola, Daniela and Mariana to follow in his footsteps and attempt to reach the stars.Adnan BashirChristian Schubert

GR@PPA 2.9: Radiation matching for simulating photon production processes in hadron collisions

We release an event generator package GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown large contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the installation and execution of the programs in this article. The practical performance is also presented. Program summaryProgram Title: GR@PPA 2.9Program Files doi:http://dx.doi.org/10.17632/7838c8djsr.1Licensing provisions: GPLv3Programming language: Fortran; with some included libraries coded in C and C++External routines/libraries: bash and Perl for the setup, and CERNLIB, ROOT, LHAPDF 5, PYTHIA 6.4 according to the choice of usersJournal reference of previous version: Comput. Phys. Comm. 183 (2012) 1014–1028Does the new version supersede the previous version?: No, this version supports processes not included in previous versions.Nature of problem: It is necessary to include jet-associated processes up to two jets for realistic simulations of photon production processes in high-energy hadron collisions. Photons also need to be considered as radiation. An appropriate matching method has to be introduced for combining those processes having different jet and photon multiplicities and parton shower simulations.Solution method: The limited leading-log (LLL) subtraction method has been extended to multi-jet processes and those including photon radiation. The final-state parton shower simulation has been improved to support QED photon radiation.Reasons for the new version: New processes have been supported.Summary of revisions: This program package provides event generators for realistic simulations of single and double photon production processes in high-energy hadron collisions. Users can consistently combine different jet- and photon-multiplicity processes up to two jets and two photons.

Can a QED Photon Propagate Out of the Black‐Hole Horizon?

AbstractWe show at one‐loop approximation that the QED photon acquires a negative gauge‐invariant mass‐squared in the near‐horizon region of an evaporating Schwarzschild black hole. This result may imply that information about the inner structure of evaporating black holes is accessible, even without invoking the modification of the basic QFT and GR principles.

Generating double NOON states of photons in circuit QED

To generate a NOON state with a large photon number $N$, the number of operational steps could be large and the fidelity will decrease rapidly with $N$. Here we propose a method to generate a new type of quantum entangled states, $(|NN00\rangle+|00NN\rangle)/\sqrt{2}$ called "double NOON" states, with a setup of two superconducting flux qutrits and five circuit cavities. This scheme operates essentially by employing a two-photon process, i.e., two photons are simultaneously and separately emitted into two cavities when each coupler qutrit is initially in a higher-energy excited state. As a consequence, the "double" NOON state creation needs only $N$+2 operational steps. One application of double NOON states is to get a phase error of $1/(2N)$ in phase measurement. In comparison, to achieve the same error, a normal NOON state of the form $(|2N,0\rangle+|0,2N\rangle)/\sqrt{2}$ is needed, which requires at least $2N$ operational steps to prepare by using the existing schemes. Our numerical simulation demonstrates that high-fidelity generation of the double NOON states with $N\leq 10$ even for the imperfect devices is feasible with the present circuit QED technique.

The Study of the Photon Structure Functions in the ILC Energy Range

At the future $e^{+}e^{-}$ linear collider ILC/CLIC it will be able to measure the photon structure functions in a wider range of kinematic variables x and $Q^{2}$ in comparison to the previous results of experiments at LEP. The classical way to measure the photon structure functions is the study of $e^{+}e^{-} \rightarrow e^{+}e^{-} {\gamma}{\gamma} \rightarrow e^{+}e^{-}$ X process, where X is the leptonic or hadronic final state. For the study of the QED and hadronic photon structure functions the simulations of two-photon processes were performed at the ILC center-of-mass energy equal to 500 GeV using the PYTHIA and the ILCSoft package. The analysis used information related to the forward detectors, tracking detectors and calorimeters which are parts of the ILD detector concept.

Efficient generation of NOON states on two microwave-photon resonators

We present an efficient scheme for the generation of NOON states of photons in circuit QED assisted by a superconducting charge qutrit. It is completed with two kinds of manipulations, that is, the resonant operation on the qutrit and the resonator, and the single-qubit operation on the qutrit, and they both are high-fidelity operations. Compared with the one by a superconducting transmon qutrit proposed by Su et al. (Sci. Rep. 4, 3898 (2014)), our scheme does not require to maintain the qutrit in the third excited state with a long time, which relaxes the difficulty of its implementation in experiment. Moreover, the level anharmonicity of a charge qutrit is larger and it is better for us to tune the different transitions of the charge qutrit resonant to the resonator, which makes our scheme faster than others.

Fast and simple scheme for generating NOON states of photons in circuit QED.

The generation, manipulation and fundamental understanding of entanglement lies at very heart of quantum mechanics. Among various types of entangled states, the NOON states are a kind of special quantum entangled states with two orthogonal component states in maximal superposition, which have a wide range of potential applications in quantum communication and quantum information processing. Here, we propose a fast and simple scheme for generating NOON states of photons in two superconducting resonators by using a single superconducting transmon qutrit. Because only one superconducting qutrit and two resonators are used, the experimental setup for this scheme is much simplified when compared with the previous proposals requiring a setup of two superconducting qutrits and three cavities. In addition, this scheme is easier and faster to implement than the previous proposals, which require using a complex microwave pulse, or a small pulse Rabi frequency in order to avoid nonresonant transitions.

The relation between the QED charge renormalized in [formula omitted] and on-shell schemes at four loops, the QED on-shell β-function at five loops and asymptotic contributions to the muon anomaly at five and six loops

In this paper we compute the four-loop corrections to the QED photon self-energy Π(Q2) in the two limits of q=0 and Q2→∞. These results are used to explicitly construct the conversion relations between the QED charge renormalized in on-shell (OS) and MS¯ scheme. Using these relations and results of Baikov et al. [1] we construct the momentum dependent part of Π(Q2,m,α) at large Q2 at five loops in both MS¯ and OS schemes. As a direct consequence we arrive at the full result for the QED β-function in the OS scheme at five loops. These results are applied, in turn, to analytically evaluate a class of asymptotic contributions to the muon anomaly at five and six loops.

Maximal velocity of photons in non-relativistic QED

We consider the problem of propagation of photons in the quantum theory of non-relativistic matter coupled to electromagnetic radiation, which is, presently, the only consistent quantum theory of matter and radiation. Assuming that the matter system is in a localized state (i.e. for energies below the ionization threshold), we show that the probability to find photons at time t at the distance greater than ct, where c is the speed of light, vanishes as t→∞ as an inverse power of t.

REMARKS ON A CHERN–SIMONS-LIKE COUPLING

We consider the static quantum potential for a gauge theory which includes a light massive vector field interacting with the familiar U (1) QED photon via a Chern–Simons-like coupling, by using the gauge-invariant, but path-dependent, variables formalism. An exactly screening phase is then obtained, which displays a marked departure of a qualitative nature from massive axionic electrodynamics. The above static potential profile is similar to that encountered in axionic electrodynamics consisting of a massless axion-like field, as well as to that encountered in the coupling between the familiar U (1) QED photon and a second massive gauge field living in the so-called U (1)h hidden-sector, inside a superconducting box.

Strong gravitation waves in terms of Maurer-Cartan forms

Strong gravitation plane waves are represented in terms of the Maurer-Cartan spin connection coefficients in cosmological background. It was shown that the diffeo-invariance of spin connection coefficients leaves only one degree of freedom of the strong gravitation plane waves in contrast to the metric approach, where gravitation waves have two degrees of freedom like photons in QED. The Hilbert action of gravitation waves in terms of spin connection coefficients takes the form of a bilinear field theory.

The n-Qubit W State of Ground-State Atoms Using Cavity QED and Single Photon Detection

We present a simple scheme for the probabilistic generation of the n-qubit W state of three-level systems in cavity quantum electrodynamics. Once the W state is prepared, it will be insensitive to the spontaneous emission of atoms due to the fact that only the two degenerate ground states of the three-level atoms are involved. With time evolution of the system, the success probability and the experimental feasibility are also discussed.

Simplified Scheme for Testing Symmetrization Postulate for Photons

We propose a scheme for testing the small violations of thesymmetrization postulate (SP) for photons in cavity QED. In the scheme, adegenerate Λ-type three-level atom is sent through a cavity field initially ina q-deformed coherent state. After an appropriate interaction time, theatom is measured by a state-selective detector. The probability that theatom makes a transition from one of the lower states to the othercharacterizes the violation of the SP. In the scheme, only one atom isrequired and classical fields are unnecessary, which is prior to the previous schemes.