Nonreciprocal two-photon transmission and statistics in a chiral waveguide QED system

We study the nonreciprocal properties of transmitted photons in a chiral waveguide quantum electrodynamics(QED)system,including single-and two-photon transmissions and second-order correlations.For the single-photon transmission,the nonreciprocity is induced by the effects of chiral coupling and atomic dissipation in the weak coupling region.It vanishes in the strong coupling regime when the effect of atomic dissipation becomes ignorable.In the case of two-photon transmission,there exist two ways of going through the emitter:independently as plane waves and formation of bound state.Besides the nonreciprocal behavior of plane waves,the bound state that differs in two directions also alters transmission probabilities.In addition,the second-order correlation of transmitted photons depends on the interference between plane wave and bound state.The destructive interference leads to the strong antibunching in the weak coupling region,while the effective formation of bound state leads to the strong bunching in the intermediate coupling region.However,the negligible interactions for left-propagating photons hardly change the statistics of the input coherent state.

Non-Markovianity of an atom in a semi-infinite rectangular waveguide

We investigate the non-Markovianity(NM)of a waveguide QED with a two-level atom as the system and a semiinfinite rectangular waveguide as the environment,where the transverse magnetic(TM_(mn))modes define the quantum channels of guided photons.The perfect mirror imposed by the finite end exerts a retarded feedback mechanism to allow for information backflow,which leads to NM dynamics.For the energy separation of the atom far away from the cutoff frequencies of transverse modes,the delay differential equations are obtained with single-excitation initial in the atom.Our attention is focused on the effects of multiple quantum channels involved in guiding photons on the degree of nonMarkovian behavior.An asymptotic value of the non-Markovianity N_(1)can be found as the atom–mirror distance is large enough,however,the asymptotic value of N_(2)of the atom interacting with the effective double-modes is lower than that of the atom interacting with the effective single-mode.We also show that N_(1)is a constant,and the analytical expression for N_(2)is related to the parameters associated with the modes,which is related to the interference of the two modes.

Non-Markovian Master Equation for Distant Resonators Embedded in a One-Dimensional Waveguide

We develop a master equation approach to describe the dynamics of distant resonators coupled through a one-dimensional waveguide. Our method takes into account the back-actions of the reservoirs, and enables us to calculate the exact dynamics of the complete system at all times. We show that such system can cause nonexponential and long-lived photon decay due to the existence of a relaxation effect. The physical origin of non-Markovianity in our model system is the finite propagation speed resulting in time delays in communication between the nodes, and strong decay rate of the emitters into the waveguide. When the distance satisfies the standing wave condition, we find that when the time delay is increased, the dark modes formation is no longer perfect, and the average photon number of dark mode decreases in steady time limit.

Heralded hyper-CNOT gates for two-photon systems assisted by quantum scattering in waveguides

Photonic hyper-parallel quantum gates play a critical role in high-capacity quantum communication and fast quantum computing.Here,based on photon scattering in onedimensional(1D)waveguides,we present some heralded schemes for constructing four-qubit hyper-controlled-not(hyper-CNOT)gates in two-photon systems.The qubits are encoded on both the polarization and spatial-mode degrees of freedoms(DOFs)of the photons,which can simplify the quantum circuit and reduce the quantum resource consumption.In our schemes,the faulty scattering events between photons and emitters caused by system imperfections can be filtered out and discarded.That is,our protocols for hyper-CNOT gates work in a heralded way.Our calculations show that,with great progress in the emitter-waveguide systems,our photonic hyper-CNOT gates may be experimentally feasible.

The interference between a giant atom and an internal resonator

The Jaynes–Cummings model plays an important role in quantum entanglement and state measurements.Here,we discuss how to realize it in a waveguide-mediated interaction system,which comprises a giant atom and a resonator.We show the vacuum Rabi splitting and discuss how to achieve a unidirectional transport.We extend the Purcell effect in c QED to this waveguide QED system,showing how to control the giant atom decay rate.Our design can further be built experimentally and has application in quantum manipulation.