In this paper, we investigate the single-photon scattering and bound states in a one-dimensional coupled-resonator waveguide which couples to a single artificial giant atom with two or more coupling points. When the atom couples to the waveguide via two resonators, the single-photon reflection rate is characterized by either Breit-Wigner or Fano line shapes. When the atom couples to the waveguide via multiple resonators, we numerically show how the destructive interference effect leads to a complete single-photon reflection. We also find a phase transition phenomena for the multi-resonator coupling case, which reveals that the upper bound state only exists when the atom-waveguide coupling strength is above a critical value.
An electronically excited atom or molecule located outside but near a planar optical waveguide can decay by spontaneous emission of a photon into a guided mode of the waveguide. We outline a QED theory for calculating the probability for this process and describe general physical insights from that theory. A couple of representative examples are discussed in detail.
We propose a hybrid silicon waveguide scheme to avoid the impact of noise photons induced by pump lights in application scenarios of quantum photonic circuits with quantum light sources. The scheme is composed of strip waveguide and shallow-ridge waveguide structures. It utilizes the difference of biphoton spectra generated by spontaneous four wave mixing (SFWM) in these two waveguides. By proper pumping setting and signal/idler wavelength selection, the generation of desired photon pairs is confined in the strip waveguide. The impact of noise photons generated by SFWM in the shallow-ridge wav…
We report the observation of correlated photon pairs generated by spontaneous parametric down-conversion in a quasi-phase matched KTiOPO4 nonlinear waveguide. The highest ratio of coincidence to single photon count rates observed in the 830 nm wavelength region exceeds 18%. This makes nonlinear waveguides a promising source of correlated photons for metrology and quantum information processing applications. We also discuss possibilities of controlling the spatial characteristics of the down-converted photons produced in multimode waveguide structures.
We propose a single-photon frequency converter via a one-dimensional waveguide coupled to a $V$-type atom. The on-demand classical field allows the atom to absorb a photon with a given frequency, then emit a photon with a carried frequency different from the absorbed one. The absorption and re-emission process is formulated as a two-channel scattering process. We study the single-photon frequency conversion mechanism in two kinds of realistic physical system: coupled resonator waveguide with cosine dispersion relation and an optical waveguide with linear dispersion relation respectively. We fi…
We propose a scheme to generate photonic tensor network states by sequential scattering of photons in waveguide QED systems. We show that sequential scatterings can convert a series of unentangled photons into any type of matrix product states. We also demonstrate the possibility of generating projected entangled pair states with arbitrary network representation by photon re-scattering.
The resonant-cavity-enhanced (RCE) technique is an important approach to increasing the detection efficiency (DE) of typical free-space coupling photons. Here, we show that such a technique can also be utilized to increase the detection probability (DP) of a single waveguide-coupled photon. Based on a fully quantum mechanical theory in real space, we exactly calculated the absorption probability of a single photon for a two-level detector next to the waveguide. We find that the DP of the waveguide photon for the detector in a waveguide-coupled ring cavity is significantly higher than that for …
We identify a general connection between the physics of exceptional points in non-Hermitian systems and the few-photon bound states in waveguide quantum electrodynamics (QED) systems. We show that, in waveguide QED systems where the local quantum system exhibits an exceptional point, the tightest-bound few-photon bound state occurs at the exceptional point. We illustrate this connection with an explicit computation on a waveguide QED system in which a waveguide is coupled to a Jaynes-Cummings system. Our result provides a quantum signature of the exceptional point physics and indicates that th…
We experimentally show that two-photon path-entangled states can be coherently manipulated by multi-mode interference in multi-mode waveguides. By measuring the output two-photon spatial correlation function versus the phase of the input state, we show that multi-mode waveguides perform as nearly-ideal multi-port beam splitters at the quantum level, creating a large variety of entangled and separable multi-path two-photon states.
We investigate the single-photon propagation in the one-dimensional waveguide coupled to $N$ two-level atoms. For a waveguide coupled to $N$ distant atoms, the transparency can be induced by coherent interaction at resonance for an $even$ $number$ of $N$, while for an $odd$ $number$ of $N$, the photon can be fully reflected. We then can switch the photon transport by controlling the atomic number. For a waveguide coupled to a small atomic ensemble of $N$ atoms in the same position, the transparency disappears, and the photonic transport property displays a jump behavior near the resonance poin…
Bound states arise in waveguide QED systems with a strong frequency-dependence of the coupling between emitters and photonic modes. While exciting such bound-states with single photon wave-packets is not possible, photon-photon interactions mediated by the emitters can be used to excite them with two-photon states. In this letter, we use scattering theory to provide upper limits on this excitation probability for a general non-Markovian waveguide QED system and show that this limit can be reached by a two-photon wave-packet with vanishing uncertainty in the total photon energy. Furthermore, we…
We present a theoretical study of one photon wave-packet scattered by two atoms in one dimensional waveguide. We investigate the role of non rotating wave approximation terms to take into account correctly for the effects of the virtual photons that are exchanged between the atoms. These terms are shown to influence drastically the reflected and the transmitted fields, imposing strict constraints on their temporal envelopes.
We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to the photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements $β$-factors of up to 0.89 are derived, and an unprecedented large bandwidth of 20 nm is demonstrated. This shows the promising potential of photonic crystal waveguides for efficient single-photon sources. The scaled frequency where the enhancement is observed is in excellent agreement with theory taking into account that t…
This work proposes and analyses a novel approach for the generation of separable (quantum uncorrelated) photon pairs based on spontaneous parametric down-conversion in Bragg reflection waveguides composed of semiconductor AlGaN layers. This platform allows the removal of any spectral correlation between paired photons that propagate in different spatial modes. The photons can be designed to show equal or different spectra by tuning the structural parameters and hence the dispersion of the waveguide.
We report measurements of time-frequency entangled photon pairs and heralded single photons at telecommunications wavelengths, generated using a periodically-poled, lithium niobate on insulator (LNOI) waveguide pumped optically by a diode laser. We achieve a high Coincidences-to-Accidentals Ratio (CAR) at high pair brightness, a low value of the conditional self-correlation function [$g^{(2)}$(0)], and high two-photon energy-time Franson interferometric visibility, which demonstrate the high quality of the entangled photon pairs and heralded single photons.
We investigate the effect of a laser shining perpendicularly to a waveguide channeling two-level atoms. For weak transversal coupling the excitation of transverse atomic levels occurs at avoided crossings associated with "Rabi resonances" in which the Rabi frequency coincides with the transition frequency between the transverse levels.
In this article, we show that in the level of quantum mechanics, a photon position operator with commuting components can be obtained in a more natural way; in the level of quantum field theory, the photon position operator corresponds to the center of the photon number. It is most interesting for us to show that, a photon inside a waveguide can be localized in the same sense that a massive particle can be localized in free space, and just as that it is impossible to localize a massive particle with a greater precision than its Compton wavelength, one can also arrival at a similar conclusion: …
Optical parametric process occurring in a nonlinear planar waveguide can serve as a source of light with nonclassical properties. Properties of the generated fields are substantially modified by scattering of the nonlinearly interacting fields in a photonic band-gap structure inside the waveguide. A quantum model of linear operator amplitude corrections to amplitude mean-values provides conditions for an efficient squeezed-light generation as well as generation of light with sub-Poissonian photon-number statistics. Destructive influence of phase mismatch of the nonlinear interaction can fully …
Slowing/stopping the light travelling in free space with electromagnetically induced transparency to im- plement the optical quantum information processings and store information has been paid much attention in recent years. For the waveguide photons, here, we propose an approach to stop them with a controllable atomic cavity generated by a pair of atomic mirrors; one of them reflects the photon completely and an- other one with the adjustable reflected/transmitted probability of the photons. Based on the full quantum mechanical theory in real space, we show that the reflected/transmitted prob…
We report the characterization of correlated photon pairs generated in dispersion-engineered silicon slow-light photonic crystal waveguides pumped by picosecond pulses. We found that taking advantage of the 15 nm flat-band slow-light window (vg ~ c/30) the bandwidth for correlated photon-pair generation in 96 and 196 \mum long waveguides was at least 11.2 nm; while a 396 \mum long waveguide reduced the bandwidth to 8 nm (only half of the slow-light bandwidth due to the increased impact of phase matching in a longer waveguide). The key metrics for a photon-pair source: coincidence to accidental…
We study the coherent transport of one or two photons in a 1D waveguide chirally coupled to a nonlinear resonator. Analytic solutions of the one-photon and two-photon scattering is derived. Although the resonator acts as a non-reciprocal phase shifter, light transmission is reciprocal at one-photon level. However, the forward and reverse transmitted probabilities for two photons incident from either the left side or the right side of the nonlinear resonator are nonreciprocal due to the energy redistribution of the two-photon bound state. Hence, the nonlinear resonator acts as an optical diode …
We explore theoretically the single-photon transport in a single-mode waveguide that is coupled to a hybrid atom-optomechanical system in a strong optomechanical coupling regime. Using a full quantum real-space approach, transmission and reflection coefficients of the propagating single-photon in the waveguide are ob- tained. The influences of atom-cavity detuning and the dissipation of atom on the transport are also studied. Intriguingly, the obtained spectral features can reveal the strong light-matter interaction in this hybrid system.
We demonstrate a frequency multiplexed photon pair generation based on a quadratic nonlinear optical waveguide inside a cavity which confines only signal photons without confining idler photons and the pump light. We monolithically constructed the photon pair generator by a periodically-poled lithium niobate (PPLN) waveguide with a high reflective coating for the signal photons around 1600 nm and with anti-refrective coatings for the idler photons around 1520 nm and the pump light at 780 nm at the end faces of the PPLN waveguide. We observed a comb-like photon pair generation with a mode spaci…
We study the emergence of two types of two-photon bounds states in waveguides of any chirality. Specifically, we present a systematic way of analytically determining the eigenstates of a system consisting of a waveguide coupled to a partially chiral, infinite array of equidistant two-level emitters. Using an effective Hamiltonian approach, we determine the properties of the two-photon bound states by determining their dispersion relation and internal structure. The bound states come in two varieties, depending on the two-photon momentum and emitter spacing. One of these states is a long-lived …
We theoretically investigate the quantum scattering of a single-photon pulse interacting with an ensemble of $Λ$-type three-level atoms coupled to a one-dimensional waveguide. With an effective non-Hermitian Hamiltonian, we study the collective interaction between the atoms mediated by the waveguide mode. In our scheme, the atoms are randomly placed in the lattice along the axis of the one-dimensional waveguide, which closely corresponds to the practical condition that the atomic positions can not be controlled precisely in experiment. Many interesting optical properties occur in our waveguide…
We present the general structure of two-photon S matrix for a waveguide coupled to a local quantum system that supports multiple ground states. The presence of the multiple ground states results in a non-commutative aspect of the system with respect to the exchange of the orders of photons. Consequently, the two-photon S matrix significantly differs from the standard form as described by the cluster decomposition principle in the quantum field theory.
The nonlocal emitter-waveguide coupling, which gives birth to the so called giant atom, represents a new paradigm in the field of quantum optics and waveguide QED. In this paper, we investigate the single-photon scattering in a one-dimensional waveguide on a two-level or three-level giant atom. Thanks to the natural interference induced by the back and forth photon transmitted/reflected between the atom-waveguide coupling points, the photon transmission can be dynamically controlled by the periodic phase modulation via adjusting the size of the giant atom. For the two-level giant-atom setup, w…
The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work …
We investigate the generation of photon-phonon entangled states by exploiting stimulated Brillouin scattering in nanoscale waveguides. The squeezing type Hamiltonian that represents creation and annihilation of photon-phonon pairs is obtained out of the multimode photon-phonon interaction Hamiltonian in the presence of a pump field. The Bogoliubov eigenstates of the Hamiltonian, which are a coherent mix of propagating photons and phonons, show squeezing properties in the uncertainties of the collective quadrature operators. The measurement of the photonic component can provide a controllable s…
We study the controllable single-photon transport in a one-dimensional (1D) waveguide with nonlinear dispersion relation coupled to a three-level emitter in cascade configuration. An extra cavity field was introduced to drive one of the level transitions of the emitter. In the resonance case, when the extra cavity does not contain photons, the input single photon will be reflected, and when the cavity contains one photon, the full transmission of the input single photon can be obtained. In the off-resonance case, the single-photon transport can also be controlled by the parameters of the cavit…
We study the scattering process of photons confined in a one dimensional optical waveguide by a laser controlled atomic ensemble. The investigation leads to an alternative setup of quantum node controlling the coherent transfer of single photon in such one dimensional continuum. To exactly solve the effective scattering equations by using the discrete coordinate approach, we simulate the linear waveguide as a coupled resonator array at the high energy limit. We generally calculate the transmission coefficients and its vanishing at resonace reflects the good controllability of our scheme. We al…
In the paper, we show that there exists a close analogy between the behavior of de Broglie matter waves and that of electromagnetic waves inside a hollow waveguide, such that the guided photons can be treated as free massive particles subject to a relativistic quantum-mechanical equation. Inspired by the effective rest mass of guided photons and the zitterbewegung phenomenon of the Dirac electron, at variance with the well-known Higgs mechanism we present some different heuristic ideas on the origin of mass.
We investigate the transport properties of two photons inside a one-dimensional waveguide side-coupled to a single-mode nonlinear cavity. The cavity is filled with a nonlinear Kerr medium. Based on the Laplace transform method, we present analytic solution of quantum states of the transmitted and reflected two photons, which are initially prepared in a Lorentzian wave packet. The solution reveals how quantum correlation between the two photons emerge after the scattering by the nonlinear cavity. In particular, we show that the output wave function of the two photons in position space can be lo…
Entangled photons are pivotal elements in emerging quantum information technologies. While several schemes are available for the production of entangled photons, they typically require the assistance of cumbersome optical elements to couple them to other components involved in logic operations. Here, we introduce a scheme by which entangled photon pairs are directly generated as guided mode states in optical waveguides. The scheme relies on the intrinsic nonlinearity of the waveguide material, circumventing the use of bulky optical components. Specifically, we consider an optical fiber under n…
We propose an on-chip source of entangled photon pairs that uses an arrayed-waveguide grating (AWG) with multiple nonlinear input waveguides as correlated photon pair sources. The AWG wavelength-demultiplexes photon pairs created in input waveguides and simultaneously produces a high-dimensional entangled state encoded in the optical path. We implemented the device with a monolithic silicon-silica waveguide integration platform and demonstrated the entanglement of two dimensions in a proof-of-principle experiment.
We demonstrate the generation of quantum-correlated photon pairs from a Si photonic-crystal coupled-resonator optical waveguide. A slow-light supermode realized by the collective resonance of high-Q and small-mode-volume photonic-crystal cavities successfully enhanced the efficiency of the spontaneous four-wave mixing process. The generation rate of photon pairs was improved by two orders of magnitude compared with that of a photonic-crystal line defect waveguide without a slow-light effect.
Quantum photonic integration circuits are a promising approach to scalable quantum processing with photons. Waveguide single-photon-detectors (WSPDs) based on superconducting nanowires have been recently shown to be compatible with single-photon sources for a monolithic integration. While standard WSPDs offer single-photon sensitivity, more complex superconducting nanowire structures can be configured to have photon-number-resolving capability. In this work, we present waveguide photon-number-resolving detectors (WPNRDs) on GaAs/Al0.75Ga0.25As ridge waveguides based on a series connection of n…
The implementation of a fully integrated Hadamard gate on one single chip is currently one of the major goals in the quantum computation and communication community. Prerequisites for such a chip are the integration of single-photon sources and detectors into waveguide structures such as photonic crystals or slab and ridge waveguide. Here, we present an implementation of a single-photon on-chip experiment based on a III-V semiconductor platform. Individual semiconductor quantum dots were used as pulsed single-photon sources integrated in ridge waveguides, and on-chip waveguide-beamsplitter ope…
We present a heuristic mathematical model of the relation between the geometry of a photonic crystal waveguide and the Purcell enhancement factor at a particular wavelength of interest. We use this model to propose approaches to the design of a photonic crystal waveguide maximizing the Purcell enhancement at a target wavelength. Numerical simulations indicate that the proposed structures exhibit robustness to fabrication defects introduced into photonic crystal geometry.
We demonstrate experimentally the frequency time entanglement of photon pairs produced in a CW pumped quasi phased matched AlGaAs superlattice waveguide. A visibility of 96.0+-0.7% without background subtraction has been achieved, which corresponds the violation of Bell inequality by 52 standard deviations.
This review describes the emerging field of waveguide quantum electrodynamics (WQED) concerned with the interaction of photons propagating in a waveguide with localized quantum emitters. The collective emitter-photon interactions can lead to both enhanced and suppressed coupling compared to the case of independent emitters. Here, we focus on guided photons and ordered arrays, leading to super- and sub-radiant states, bound photon states and quantum correlations with promising quantum information applications. We highlight recent groundbreaking experiments performed with different quantum platf…
We propose a new scheme for quantum computation using flying qubits--propagating photons in a one-dimensional waveguide--interacting with matter qubits. Photon-photon interactions are mediated by the coupling to a three- or four-level system, based on which photon-photon π-phase gates (Controlled-NOT) can be implemented for universal quantum computation. We show that high gate fidelity is possible given recent dramatic experimental progress in superconducting circuits and photonic-crystal waveguides. The proposed system can be an important building block for future on-chip quantum networks.
We extend the input-output formalism of quantum optics to analyze few-photon transport in waveguides with an embedded qubit. We provide explicit analytical derivations for one and two-photon scattering matrix elements based on operator equations in the Heisenberg picture.
Interfacing solid-state emitters with photonic structures is a key strategy for developing highly efficient photonic quantum technologies. Such structures are often organised into two distinct categories: nanocavities and waveguides. However, any realistic nanocavity structure simultaneously has characteristics of both a cavity and waveguide, which is particularly pronounced when the cavity is constructed using low-reflectivity mirrors in a waveguide structure with good transverse light confinement. In this regime, standard cavity quantum optics theory breaks down, as the waveguide character o…
We describe theoretically the process of spontaneous parametric down-conversion in quadratic nonlinear waveguide arrays in the presence of linear loss. We derive a set of discrete Schrodinger-type equations for the biphoton wave function, and the wave function of one photon when the other photon in a pair is lost. We demonstrate effects arising from loss-affected interference between the generated photon pairs and show that nonlinear waveguide arrays can serve as a robust loss-tolerant integrated platform for the generation of entangled photon states with non-classical spatial correlations.
We consider a system where a waveguide is coupled to a cavity embedded with a two-level system (TLS), and study the effects when a two-photon quantum state is injected into the waveguide. The wave function of two outgoing photons is exactly solved using the Lehmann-Symanzik-Zimmermann (LSZ) reduction formalism. Our results explicitly exhibit the photon blockade effects in the strong atom-cavity coupling regime. The quantum statistical characters of the outgoing photons, including the photon bunching and anti-bunching behaviors, are also investigated in both the strong and weak coupling regimes…
Zak phase, i.e. the Berry phase acquired during an adiabatic motion of a Bloch particle across the Brillouin zone, provides a measure of the topological invariant of Bloch bands in one-dimensional crystalline potentials. Here a photonic structure, based on engineered lattices of evanescently-coupled optical waveguides, is proposed to detect Zak phase difference of photons undergoing Bloch oscillations in topologically distinct Bloch bands of dimerized superlattices.
Atoms coupled to nanophotonic interfaces represent an exciting frontier for the investigation of quantum light-matter interactions. While most work has considered the interaction between statically positioned atoms and light, here we demonstrate that a wealth of phenomena can arise from the self-consistent interaction between atomic internal states, optical scattering, and atomic forces. We consider in detail the case of atoms coupled to a one-dimensional nanophotonic waveguide, and show that this interplay gives rise to self-organization of atomic positions along the waveguide, which can be p…
The virial expansion for cold two-component Fermi and Bose atomic gases is considered in the presence of a waveguide and in the vicinity of a Feshbach resonance. The interaction between atoms and the coupling with the Feshbach molecules is modeled using a quantitative separable two-channel model. The scattering phase-shift in an atomic waveguide is defined. This permits us to extend the Beth-Uhlenbeck formula for the second-order virial coefficient to this inhomogeneous case.
We suggest a method for trapping photons in quasi one-dimensional waveguide or coupled-resonator lattices, which is based on an optical analogue of the Aharonov-Bohm cages for charged particles. Light trapping results from a destructive interference of Aharonov-Bohm type induced by a synthetic magnetic field, which is realized by periodic modulation of the waveguide/resonator propagation constants/resonances.
We report on the demonstration of correlated photon pair generation in quasi-phase-matched superlattice AlGaAs waveguides with a high coincidence-to-accidental ratio (CAR); with a continuous (CW) pump, the observed CAR (>100) is more than two order of magnitudes improvement over previously reported spontaneous down conversion (SPDC) schemes in AlGaAs waveguides with a pulsed pump.
