Single-photon Transport Research Articles

Single-photon circulator by spinning optical resonators

A circulator is one of the crucial devices in quantum networks and simulations. We propose a four-port circulator that regulates the flow of single photons at muti-frequency points by studying the coherent transmission of a single photon in a coupled system of two resonators and two waveguides. When both resonators are static or rotate at the same angular velocity, the single-photon transport demonstrates reciprocity; however, when the angular velocities differ, four distinct frequency points emerge where photon circulation can occur. In particular, when the angular velocities of the two resonators are equal and opposite, there are two different frequency points where photon circulation can be achieved, and there is a frequency point where a single photon input from any waveguide can be completely routed to the other waveguide. Interestingly, by rotating the two resonators, the single-photon circulation suppressed by the internal defect-induced backscattering can be restored.

Dynamical theory of single-photon transport through a qubit chain coupled to a one-dimensional nanophotonic waveguide

We study the dynamics of a single-photon pulse traveling through a linear qubit chain coupled to continuum modes in a one-dimensional (1D) photonic waveguide. We derive a time-dependent dynamical theory for qubits’ amplitudes and for transmitted and reflected spectra. We show that the requirement for the photon-qubit coupling to exist only for positive frequencies can significantly change the dynamics of the system. First, it leads to the additional photon-mediated dipole-dipole interaction between qubits which results in the violation of the phase coherence between them. Second, the spectral lines of transmitted and reflected spectra crucially depend on the shape of the incident pulse and on the initial distance between the pulse center and the first qubit in the chain. We apply our theory to one-qubit and two-qubit systems. For these cases we obtain the explicit expressions for the qubits’ amplitudes and for the photon radiation spectra as time tends to infinity. Specific calculations are performed for superconducting qubits operating in GHz frequency range. For the incident Gaussian wave packet we calculate the line shapes of transmitted and reflected photons.

Efficient single-photon directional transfer between waveguides via two giant atoms.

We investigate the single-photon transport properties in a double-waveguide quantum electrodynamic system. We force the energy degeneracy of the collective states by adjusting the direct coupling strength between the two giant atoms. Our results indicate that resonant photons can be completely transferred between the two waveguides owing to the scattering interference of eigenstates, which also results in the directional propagation of resonant photons in the output waveguide. Perfect transfer occurs when the two scattering states degenerate in the energy and decay rates. We further propose a simple scheme to realize the efficient photon transfer with directional control. This study has potential applications in quantum networks and integrated photonic circuits.

Construction of 3D MoSx/Zn2In2S5 nanoflower heterojunction for boosted photothermal-assisted photocatalytic hydrogen evolution in biomass solution

Hydrogen production from solar energy conversion method is an attractive strategy to alleviate the energy crisis. The use of non-noble metal cocatalysts instead of noble metal monomers to improve the performance of photocatalytic hydrogen evolution reactions has been pursued by researchers. In this work, we develop a single-photon excited electron transport pathway system for photocatalytic hydrogen production performance studies by coupling 0D MoSx nanodots and 3D Zn2In2S5 nanoflowers. Experimental results combined with DFT calculations show that MoSx not only imparts photothermal properties to the composite material, but also acts as a conduit for electron transport, which can accelerate the rapid separation and transfer of photocatalytic charges. Among them, 3-MoSx/Zn2In2S5 selectively promoted photocatalyzed conversion of benzyl alcohol (BA, 100% conversion) into benzaldehyde (BAD, 96.82% selectivity) by simultaneous co-production of hydrogen (8.74 mmol•g−1•h−1) within 1 h, which is about 7.80 and 2.69 times higher than pure Zn2In2S5, respectively. Further, 3-MoSx/Zn2In2S5 can realize the hydrogen production reaction with glycerol as the substrate with a remarkable effect (up to 5.47 mmol•g−1•h−1). Additionally, 3-MoSx/Zn2In2S5 also showed some hydrogen production performance when other biomasses (glucose, xylose, and cellulose) were used as substrates. This work provides a feasible strategy for the design of photothermal photocatalysts for synergistic hydrogen production from biomass.

Band gap engineering and controlling transport properties of single photons in periodic and disordered Jaynes–Cummings arrays

We theoretically study the single-photon transport properties in periodic and position-disordered Jaynes–Cummings (or JC) arrays of waveguide-coupled microtoroidal ring resonators, each interacting with a single two-level quantum emitter. Employing the real-space formalism of quantum optics, we focus on various parameter regimes of cavity quantum electrodynamics (cQED) to gain better control of single-photon propagation in such a many-body quantum optical setting. As for some of the key findings, we observe that the periodic setting leads to the formation of the band structure in the photon transmission spectra, which is most evident in the strong coupling regime of cQED. However, under resonant conditions with no losses, the application of Bloch’s theorem indicates that the width of forbidden gaps can be altered by tuning the emitter-cavity coupling to small values. Moreover, in the disordered case, we find that the single-photon transmission curves show the disappearance of band formation. However, spectral features originating from cQED interactions observed for the single atom-cavity problem remain robust against weak-disordered conditions. The results of this work may find application in the study of quantum many-body effects in the optical domain as well as in different areas of quantum computation and quantum networking.

Controllable single-photon transport mediated by a time-modulated Jaynes–Cummings model

Controllable single-photon scattering in a one-dimensional waveguide coupled to a Jaynes–Cummings structure containing a time-modulated two-level atom interacting with a single-mode cavity is investigated. The photon transmission and reflection amplitudes are calculated by using an effective Floquet Hamiltonian in real space. The results show that the coupling between the atom and the cavity mode can dynamically be tuned via periodically modulating the atomic transition frequency. As a consequence, the scattering behaviors of the waveguide photons can be actively manipulated, and a controllable single-photon switch with high on-off ratio could be realized. More interestingly, the switch works well within a wide frequency region, i.e., the transmission of both resonant and off-resonant waveguide photons can be effectively switched on or off with appropriate system parameters. Furthermore, the proposed dynamically tunable switching scheme is robust against atomic dissipation associated with the help of atom-cavity coupling mismatch. Such single-photon device can be used as an elementary unit for various quantum information processing.

Resonator mediated controlling single photon transport in one-dimensional waveguide coupling to a giant atom

We theoretically investigate coherent controlling single photon transport in one-dimensional waveguide coupled to a giant atom interacting with a resonator. The giant atom is considered as a Λ-type system. One transition of the atom couples to the waveguide and the other one is driven by the resonator. Single photon scattering amplitudes are calculated for three kinds of coupling schematics, respectively. Both the analytical and numerical results show that single photon scattering properties can be manipulated by adjusting the size of the giant atom, the coupling strengths of the waveguide-resonator and resonator-giant atom. Specifically, the transmission spectra exhibit two Rabi-splitting dips and the locations of the dips are strongly dependent on the size of the giant atom (GA). It also shows that the resonant single photon can be tuned from being transmitted to being reflected by controlling the coupling strength. Our results may find applications in designing quantum devices based on giant atom at single-photon level.

Temperature-related single-photon transport in a waveguide QED.

We propose a scheme to realize a novel, to the best of our knowledge, scenario that the single-photon transport in a one-dimensional waveguide can be affected by the temperature. The scheme is composed by a waveguide-atom interacting structure linked to a thermal bath. The single-photon reflection (or transmission) coefficient can be controlled by adjusting the temperature of the thermal bath. This provides a thermal control of the single-photon transport. Moreover, the scheme provides an approach for implementing the optical thermometer, in which the temperature of the thermal bath is estimated by measuring the photonic transport. The thermometer can accurately measure the temperature in the low-temperature region.

Phase-tunable single-photon transport in a one-dimensional waveguide with the extra cavity–emitter system

Phase-tunable single-photon transport in a one-dimensional waveguide with the extra cavity–emitter system

Single-photon Transport in a Waveguide-cavity-emitter System

We investigate the single-photon transport properties in a hybrid waveguide quantum electrodynamics system, in which a one-dimensional waveguide is simultaneously coupled to a cavity and a driven Λ-type three-level atom. The cavity and the atom are also coupled to each other. We show that when the waveguide is coupled to the cavity and the atom at the same point, double electromagnetically induced transparency (EIT) can be observed from the system. The physical mechanism of the double EIT effect has been given by setting up the eigenstate structure for the whole system. When the waveguide is coupled to the cavity and the atom at different points, we demonstrate that the controllable nonreciprocal scattering effect can be achieved by modulating the non-zero cavity-emitter separation and the phase associated with the cavity-emitter coupling strength. These results have potential applications in realization of photonic coherent control.

Phase-modulated single-photon nonreciprocal transport and directional router in a waveguide–cavity–emitter system beyond the chiral coupling

We propose a potentially practical scheme for the controllable single-photon transport via waveguides which are coupled to a microcavity–emitter system. The microcavity–emitter system consists of a V-type three-level emitter and two or one single-mode microcavity. A driving field is used to drive a hyperfine transition between two upper excited states of the V-type three-level emitter. Beyond chiral coupling between waveguides and microcavity–emitter system, we show that the perfectly nonreciprocal single-photon transport in a single waveguide and the single-photon router with 100% routing probability in two waveguides can be achieved. Interesting enough, whether the nonreciprocal single-photon transport or the single-photon router can be switched periodically by adjusting the phase associated with microcavity–emitter coupling strength and the driving field. The complete physical explanation of the underlying mechanism is presented.

Three methods for the single-photon transport in a chiral cavity quantum electrodynamics system

We investigate the single-photon transport problem in the system of a Whispering-Gallery mode microresonator directionally coupled with a two-level quantum emitter (QE). This QE-microresonator coupling system can usually be studied by cavity quantum electrodynamics and the single-photon transport methods. However, we find that if we treat a two-level QE as a single-photon phase-amplitude modulator, we can also deal with such systems using the transfer matrix method. Further, in theory, we prove that these three methods are equivalent. The corresponding relations of respective parameters among these approaches are precisely deduced. Our work can be extended to a multiple-resonator system interacting with two-level QEs in a chiral way. Therefore, the transfer matrix method may provide a convenient and intuitive form for exploring more complex chiral QE-resonator interaction systems.

Manipulating single-photon transport in a waveguide-QED structure containing two giant atoms

We investigate coherent single-photon transport in a waveguide-QED structure containing two giant atoms. The unified analytical expressions of the single-photon scattering amplitudes applicable for different topological configurations are derived. The spectroscopic characteristics in different parameter regimes, especially the asymmetric Fano line shapes and the electromagnetically induced transparency (EIT)-like spectra, are analyzed in detail. Specifically, we find that the appearance of Fano line shapes is influenced by not only the phase delays between coupling points but also the topologies of system. We also summarize the general conditions for appearance of EIT-like spectra by analyzing the master equation and verify these conditions by checking the corresponding analytical expressions of the scattering spectra. These phenomena may provide powerful tools for controlling and manipulating photon transport in future quantum networks.

Imaging through dynamical scattering media by two-photon absorption detectors.

Imaging through a dynamical opaque scattering medium is an almost impossible task, where strong multiple light scattering from moving scatters dynamically prevents imaging formations even with state-of-art techniques like correlation imaging or adaptive optics. Meanwhile, a small number of ballistic photons can still penetrate through but require demanding detection in terms of a ultrashort time gate and high sensitivity. However, visible light is strongly scattered for most of scattering media. Here we experimentally demonstrate a non-invasive coherent imaging scheme based on two-photon absorption capable of imaging through dynamical scattering media with a length equivalent to 28 times mean free paths for single photon transport, where two-photon absorption in a conventional semiconductor photodetector when phase matching is not required works over a wide bandwidth so it can support a fast time gate down to femtosecond level, short enough to distinguish ballistic photons from scattering background, and allows accessing longer wavelengths for deeper penetration. This technique combined with successful optical coherence tomography may pave a new way for imaging through fog, storm, and rain as well as biomedical imaging applications.

Nonreciprocal single-photon router in quantum networks

High-efficiency single-photon routing of photon signals between different quantum channels is of great importance for the quantum networks with the ability to coherently transfer quantum states between the desired sender and receiver nodes. We proposed an efficient scheme for realizing quantum routers via multiple semi-infinite coupled-resonator waveguides (CRWs) coupled to cavities nonreciprocally. Numerical results show that with the change of the phase difference value, the quantum routing function of multiple output ports can be realized, in the meantime, the information conversion rate can almost reach 100%. The optimal conditions for these phenomena are obtained by the time-reversal symmetry breaking the nonreciprocal of the single-photon transport. Moreover, we have also described a scalable scheme that can extend the router to an arbitrary number of outputs. Our results pave the way to design high-quality quantum devices based on breaking time-reversal symmetry waveguide-cavity systems.

Fano interference and transparency in a waveguide-nanocavity hybrid system with an auxiliary cavity* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11774262 and 11975023).

We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities, which are denoted by the first cavity and the auxiliary cavity. Two cases with no atom and one atom embedded in the first cavity are discussed. The Fano dips in the transmission spectrum and locations of transparency window are calculated. When no atom is embedded in the first cavity, there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant. The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide. When one atom is embedded in the first cavity, we show that the transparency window exists even though the first cavity, the atom and the auxiliary cavity are resonant. The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength. Our results have potential applications in design of quantum devices at the level of single photon, such as single photon switch and single photon routers.

Realization of single-photon transport in one-dimensional coupled-resonator waveguides via phase control

We study theoretically the influence of the phase difference of the coupling strength changes on the transport of a single-photon in coupled-resonator waveguides (CRWs). Two cases are considered: single-photon transport in a one-dimensional CRW with nonlocal coupling to a cavity, and a single-photon in a waveguide consisting of two coupled semi-infinite CRWs, which are coupled to a cavity and two cavities. The results show that the phase difference of the coupling strength can not only improve the conversion efficiency of single-photon transport in CRWs but also can adjust the irregular energy band spectrum to become regular. This will provide an important physical parameter for the experimental realization of quantum solid-state devices such as quantum switches and quantum routers.

Single-photon transport in waveguides chirally coupled to atoms

We study the single-photon transport in the scheme composed by N two-level atoms chirally coupled to N + 1 one-dimensional waveguides. The single-photon transport property relates to the chirality and the interference resulting from the scattering. The outcomes provide the potential applications for the optical quantum net and the realization of single photons with ultra-narrow band.

Controlling single-photon scattering in a rectangular waveguide by a V-type three-level emitter.

The single-photon scattering by a V-type three-level emitter in a rectangular waveguide is studied. Here the frequency value of input photons can be large beyond the single-transverse-mode region. By using Green's function formalism, the necessary and sufficient conditions of complete transmission as well as complete reflection are derived analytically. In the region of single transverse mode, the physical mechanisms of complete transmission and complete reflection are electromagnetically induced transparency (EIT) and Fano resonance, respectively. In the region of multiple transverse modes, which are induced by the finite cross section, the quantum interference between multiple scattering pathways with different transverse modes can be used to manipulate the single-photon transport. We find that the emitter becomes transparent when the superposition of waveguide modes has zero amplitude at the position of emitter. And the perfect reflection is absent even under Fano resonance unless the input-state is in a coherent superposition state. These results may promote the development of single-photon devices with wide applicable frequency region.

Unidirectional transmission of single photons under nonideal chiral photon-atom interactions

Single-photon transport in non-ideal chiral photon-atom interaction structures generally contains information backflow and thus limits the capabilities to transfer information between distant emitters in cascaded quantum networks. Here, in the non-ideal chiral case, a V -type atom coupled to a waveguide is proposed to realize completely unidirectional transmission of the single photons in a superposition state of different frequencies. A microwave field is introduced to drive the two excited states of the atom and results in photon conversion between two transitions. By adjusting the Rabi frequency and the phase of the external driving field, the transport behaviors of incident photons with specific frequencies can be optimized to complete transmission or reflection. Based on the constructive interferences between photons from different traveling paths, the transmission probabilities of the specific-frequency photons could be enhanced. Due to photon conversions with compensating the dissipations and ensuring the complete destructive interference, the ideal unidirectional transmission contrast can be maintained to 1, even when the atom has dissipations into the non-waveguide modes.