Orbital-Angular-Momentum Multiplexed Continuous-Variable Entanglement from Four-Wave Mixing in Hot Atomic Vapor

Deterministic All-Optical Quantum Teleportation of Four Degrees of Freedom

Quantum teleportation, disembodied transfer of the unknown quantum state between two locations, has been experimentally demonstrated for both discrete and continuous variable states in one degree of freedom (DOF). Generally, multiple DOFs are needed to fully characterize a quantum state. Therefore, to implement intact quantum teleportation, multiple DOFs of quantum state should be teleported simultaneously. Recently, teleporting a single photon encoded in two DOFs has been experimentally demonstrated in discrete variable regime. However, the teleportation of more than two DOFs remains unexplored. Here, by utilizing continuous variable hyperentanglement in four DOFs (azimuthal and radial indexes of Laguerre-Gaussian mode, frequency, and polarization), we experimentally demonstrate deterministic all-optical quantum teleportation of four DOFs. Moreover, we experimentally construct 24 parallel teleportation channels. Our results pave the way for deterministically implementing multiple-DOF quantum communication protocols.

Orbital Angular Momentum Multiplexed Deterministic All-Optical Quantum Erasure-Correcting Code

Quantum erasure-correcting code, which corrects the erasure in the transmission of quantum information, is an important protocol in quantum information. In the continuous variable regime, the feed-forward technique is needed for realizing quantum erasure-correcting code. This feed-forward technique involves optic-electro and electro-optic conversions, limiting the bandwidth of quantum erasure-correcting code. Moreover, in the previous continuous variable quantum erasure-correcting code, only two modes are protected against erasure, limiting the applications of quantum erasure-correcting code in high-capacity quantum information processing. In this Letter, by utilizing the orbital angular momentum (OAM) multiplexed entanglement in the encoding part and replacing the feed-forward technique with OAM mode-matched phase-sensitive amplifier in the decoding part, we experimentally demonstrate a scheme of OAM multiplexed deterministic all-optical quantum erasure-correcting code. We experimentally demonstrate that four orthogonal modes can be simultaneously protected against one arbitrary erasure. Our results provide an all-optical platform to implement quantum erasure-correcting code and may have potential applications in implementing all-optical fault-tolerant quantum information processing.

Enhancing and flattening multiplexed quantum entanglement by utilizing perfect vortex modes

We experimentally demonstrate a method for enhancing and flattening multiplexed entanglement in the four-wave mixing (FWM) process, which is implemented by replacing Laguerre-Gaussian (LG) modes with perfect vortex (PV) modes. For the topological charge l ranging from -5 to 5, the entanglement degrees of orbital angular momentum (OAM) multiplexed entanglement with PV modes are all larger than those of OAM multiplexed entanglement with LG modes. More importantly, for OAM multiplexed entanglement with PV modes, the degree of entanglement almost does not change with the topology value. In other words, we experimentally flatten the OAM multiplexed entanglement, which cannot be achieved in OAM multiplexed entanglement with LG modes based on the FWM process. In addition, we experimentally measure the entanglement with coherent superposition OAM modes. Our scheme provides a new, to the best of our knowledge, platform to construct an OAM multiplexed system and may find potential applications in realizing the parallel quantum information protocols.

Programmable time-multiplexed squeezed light source

One of the leading approaches to large-scale quantum information processing (QIP) is the continuous-variable (CV) scheme based on time multiplexing (TM). As a fundamental building block for this approach, quantum light sources to sequentially produce time-multiplexed squeezed-light pulses are required; however, conventional CV TM experiments have used fixed light sources that can only output the squeezed pulses with the same squeezing levels and phases. We here demonstrate a programmable time-multiplexed squeezed light source that can generate sequential squeezed pulses with various squeezing levels and phases at a time interval below 100 ns. The generation pattern can be arbitrarily chosen by software without changing its hardware configuration. This is enabled by using a waveguide optical parametric amplifier and modulating its continuous pump light. Our light source will implement various large-scale CV QIP tasks.

Intensity instability and correlation in amplified multimode wave mixing

The dynamics of optical nonlinearity in the presence of gain and feedback can be complex leading to chaos in certain regimes. Temporal, spectral, spatial, or polarization instability of optical fields can emerge from chaotic response of an optical \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi ^{(2)}$$\end{document}χ(2) or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi ^{(3)}$$\end{document}χ(3) nonlinear medium placed between two cavity mirrors or before a single feedback mirror. The complex mode dynamics, high-order correlations, and transition to instability in these systems are not well known. We consider a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi ^{(3)}$$\end{document}χ(3) medium with amplified four-wave mixing process and study noise and correlation between multiple optical modes. Although individual modes show intensity instability, we observe relative intensity noise reduction close to the standard quantum noise, limited by the camera speed. We observe a relative noise reduction of more than 20 dB and fourth-order intensity correlation between four spatial modes. More than 100 distinct correlated quadruple modes can be generated using this process.

Highly efficient detection of near-infrared optical vortex modes with frequency upconversion

Vortex beams carrying orbital angular momentum (OAM) have been widely applied in optical manipulations, optical micromachining, and high-capacity optical communications. Vortex mode detection is very important in various applications. However, the detection of near-infrared vortex modes is still difficult because of the wavelength limitations of the detection device. Here, we present a study on measuring optical near-infrared vortex modes with frequency upconversion, which can convert a near-infrared beam into a visible beam. In our experiment, the optical near-infrared vortex modes can be measured by the number and orientation of the fringes of the second harmonic intensity patterns. The proposed method is a convenient and flexible way to measure the different OAM of vortex beams, which may have potential applications in all kinds of circumstances that vortex modes involve.

Dynamically tunable vortex four-wave mixing in a six-level system

We investigate the orbital angular momentum of vortex light in a six-level atomic system with a closed loop. We find that a vortex light field via four-wave mixing (FWM) is sensitive to the relative phase of the driving fields due to forming a closed loop configuration. Thus, it could periodically tune the phase and intensity of the vortex FWM field by adjusting the relative phase of the driving fields. Moreover, the spatial modulation of the vortex FWM phase and intensity also can be achieved by tuning the intensity of the microwave field and detuning of the driving fields.

Azimuthal and radial modulation of double-four-wave mixing in a coherently driven graphene ensemble

We investigate in detail the azimuthal and radial modulation (i.e., the azimuthal order l_j and radial order p_j with j = 1, 2) of double-four-wave mixing (double-FWM) by use of two higher-order Laguerre-Gaussian (LG) beams in a Landau quantized graphene ensemble. A pair of weak probe pulses in the graphene ensemble interacts with two LG beams and thus two vortex FWM fields with the opposite vorticity are subsequently generated. In combination with numerical simulations, we reveal that (i) there appear l₁ + l₂ periods of phase jumps in the phase profiles under any conditions; (ii) p + 1 concentric rings emerge in the intensity profile and the strength is mainly concentrated on the inner ring when the two LG beams have the same radial orders (i.e., p₁ = p₂ = p); (iii) there are p raised narrow rings occurring in the phase profile in the case of p₁ = p₂ = p and l₁ ≠ l₂, and the raised narrow rings would disappear when p₁ = p₂ and l₁ = l₂; (iv) p_max + 1 concentric rings appear in the intensity profile, meanwhile, |p₁ - p₂| convex discs and p_min raised narrow rings emerge in the phase diagram in the case of p₁ ≠ p₂, here p_max = max(p₁, p₂) and p_min = min(p₁, p₂). Moreover, the two generated FWM fields have the same results, and the difference is that the phase jumps are completely opposite. These findings may have potential application in graphene-based nonlinear optical device by using LG beams with adjustable mode orders.

Macroscopic and deterministic quantum feature generation via phase basis quantization in a cascaded interferometric system

Quantum entanglement is the quintessence of quantum information science governed by quantum superposition mostly limited to a microscopic regime. For practical applications, however, macroscopic entanglement has an essential benefit for quantum sensing and metrology to beat its classical counterpart. Recently, a coherence approach for entanglement generation has been proposed and demonstrated in a coupled interferometric system using classical laser light, where the quantum feature of entanglement has been achieved via phase basis superposition between identical interferometric systems. Such a coherence method is based on the wave nature of a photon without violating quantum mechanics under the complementarity theory. Here, a method of phase basis quantization via phase basis superposition is presented for macroscopic entanglement in an interferometric system, which is corresponding to the energy quantization of a photon.

Orbital Angular Momentum Multiplexed Quantum Dense Coding

To beat the channel capacity limit of conventional quantum dense coding (QDC) with fixed quantum resources, we experimentally implement the orbital angular momentum (OAM) multiplexed QDC (MQDC) in a continuous variable system based on a four-wave mixing process. First, we experimentally demonstrate that the Einstein-Podolsky-Rosen entanglement source coded on OAM modes can be used in a single channel to realize the QDC scheme. Then, we implement the OAM MQDC scheme by using the Einstein-Podolsky-Rosen entanglement source coded on OAM superposition modes. In the end, we make an explicit comparison of channel capacities for four different schemes and find that the channel capacity of the OAM MQDC scheme is substantially enhanced compared to the conventional QDC scheme without multiplexing. The channel capacity of our OAM MQDC scheme can be further improved by increasing the squeezing parameter and the number of multiplexed OAM modes in the channel. Our results open an avenue to construct high-capacity quantum communication networks.

Multidimensional four-wave mixing signals detected by quantum squeezed light

Quantum light and its statistics provide powerful tools for the study of properties of matter that are difficult to retrieve with classical light. Novel spectroscopic and sensing techniques based on quantum light sources can reveal information about complex material systems that is not accessible by varying the frequencies or time delays of classical light pulses. Here, based on a four-wave mixing process, we report an experimental study of the 2D quantum noise spectra of two-beam intensity difference squeezing. External noise erodes the resolution of classical measurements, while quantum signals remain intact. Our results pave the way for exploiting quantum correlations of squeezed light for spectroscopic applications.

Four-wave mixing (FWM) of optical fields has been extensively used in quantum information processing, sensing, and memories. It also forms a basis for nonlinear spectroscopies such as transient grating, stimulated Raman, and photon echo where phase matching is used to select desired components of the third-order response of matter. Here we report an experimental study of the two-dimensional quantum noise intensity difference spectra of a pair of squeezed beams generated by FWM in hot Rb vapor. The measurement reveals details of the χ(3) susceptibility dressed by the strong pump field which induces an AC Stark shift, with higher spectral resolution compared to classical measurements of probe and conjugate beam intensities. We demonstrate how quantum correlations of squeezed light can be utilized as a spectroscopic tool which unlike their classical counterparts are robust to external noise.

Experimental Demonstration of a Multifunctional All-Optical Quantum State Transfer Machine

Quantum information protocol with quantum resources shows a great advantage in substantially improving security, fidelity, and capacity of information processing. Various quantum information protocols with diverse functionalities have been proposed and implemented. However, in general, the present quantum information system can only carry out a single information protocol or deal with a single communication task, which limits its practical application in the future. Therefore, it is essential to develop a multifunctional platform compatible with multiple different quantum information protocols. In this Letter, by utilizing an all-optical platform consisting of a gain-tunable parametric amplifier, a beam splitter, and an entanglement source, we experimentally realize the partially disembodied quantum state transfer protocol, which links the all-optical quantum teleportation protocol and the optimal 1→N coherent state cloning protocol. As a result, these three protocols, which have different physical essences and functionalities, are implemented in a single all-optical machine. In particular, we demonstrate that the partially disembodied quantum state transfer protocol can enhance the state transfer fidelity compared with all-optical quantum teleportation under the same strength of entanglement. Our all-optical quantum state transfer machine paves a way to implement the multifunctional quantum information system.

Spatially dependent hyper-Raman scattering in five-level cold atoms

We demonstrate a scheme to control the spatially dependent hyper-Raman scattering based on electromagnetically induced transparency in a cold atomic system. By adjusting the different system parameters, one can effectively modulate the phase and intensity of the generated Raman field. Specifically, we show that electromagnetically induced transparency creates quantum interference, which results in greatly enhanced efficiency for the generated Raman field. Such improvement in Raman efficiency makes our scheme suitable for generation of short-wavelength coherent radiation, conversion of frequency, and nonlinear spectroscopy based on orbital angular momentum light.

Nonlinear interferometric surface-plasmon-resonance sensor

A nonlinear interferometer can be constructed by replacing the beam splitter in the Mach-Zehnder interferometer with four-wave mixing (FWM) process. Meanwhile, the conventional surface plasmon resonance (SPR) sensors can be extensively used to infer the information of refractive index of the sample to be measured via either angle demodulation technique or intensity demodulation technique. Combined with a single FWM process, a quantum SPR sensor has been realized, whose noise floor is reduced below standard quantum limit with sensitivity unobtainable with classical SPR sensor. Therefore, in this work we have theoretically proposed a nonlinear interferometric SPR sensor, in which a conventional SPR sensor is placed inside nonlinear interferometer, which is called as I-type nonlinear interferometric SPR sensor. We demonstrate that near resonance angle I-type nonlinear interferometric SPR sensor has the following advantages: its degree of intensity-difference squeezing, estimation precision ratio, and signal-noise-ratio are improved by the factors of 4.6 dB, 2.3 dB, and 4.6 dB respectively than that obtained with a quantum SPR sensor based on a single FWM process. In addition, the theoretical principle of this work can also be expanded to other types of sensing, such as bending, pressure, and temperature sensors based on a nonlinear interferometer.

Characterization of quantum squeezing generated from the phase-sensitive and phase-insensitive amplifiers in the ultra-low average input photon number regime

We give the general expressions of intensity-difference squeezing (IDS) generated from two types of optical parametric amplifiers [i.e. phase-sensitive amplifier (PSA) and phase-insensitive amplifier (PIA)] based on the four-wave mixing process, which clearly shows the IDS transition between the ultra-low average input photon number regime and the ultra-high average input photon number regime. We find that both the IDS of the PSA and the IDS of the PIA get enhanced with the decrease of the average input photon number especially in the ultra-low average input photon number regime. This result is substantially different from the result in the ultra-high average input photon number regime where the IDS does not vary with the average input photon number. Moreover, under the same intensity gain, we find that the optimal IDS of the PSA is better than the IDS of the PIA in the ultra-low average input photon number regime. Our theoretical work predicts the presence of strong quantum correlation in the ultra-low average input photon number regime, which may have potential applications for probing photon-sensitive biological samples.

Large-Scale Quantum Network over 66 Orbital Angular Momentum Optical Modes

Multipartite entanglement (ME) is the fundamental ingredient for building quantum networks. The scale of ME determines its quantum information carrying and processing capability. Most of the current efforts for boosting the scale of ME focus on increasing the number of entangled nodes. However, the number of channels for broadcasting ME is also an important index for characterizing its scale. In this Letter, we experimentally exploit orbital angular momentum multiplexing and the spatial pump shaping technique to simultaneously and deterministically generate 11 channels of individually accessible and mutually orthogonal continuous variable (CV) spatially separated hexapartite entangled states over 66 optical modes in a single quantum system. These results suggest that our method can greatly expand the scale of ME and provide a new perspective and platform to construct a CV quantum network.

High-fidelity heralded quantum squeezing gate based on entanglement

Squeezing operation is critical in Gaussian quantum information. A high-fidelity heralded squeezing gate was recently realized using a noiseless linear amplifier with moderate ancillary squeezing. Here we analyze the heralded scheme based on squeezing [J. Zhao, Nat. Photonics, 14, 306 (2020)] and find that its fidelity depends heavily on the purity of auxiliary squeezing, and even the fidelity with a 6 dB pure squeezed state is better than with a 15 dB thermal squeezed state. On this basis, we construct a new heralded squeezing gate based on teleportation, which can overcome the shortcomings of the heralded scheme based on squeezing and is immune to the purity of input squeezing. It can better use the current best available squeezing (15 dB) to realize a perfect squeezing gate for fault-tolerant continuous-variable quantum computation. This scheme is promising to realize other single-mode Gaussian operations and non-classical state squeezing operations.

Orbital angular momentum multiplexed deterministic all-optical quantum teleportation

Quantum teleportation is one of the most essential protocol in quantum information. In addition to increasing the scale of teleportation distance, improving its information transmission capacity is also vital importance for its practical applications. Recently, the orbital angular momentum (OAM) of light has attracted wide attention as an important degree of freedom for realizing multiplexing to increase information transmission capacity. Here we show that by utilizing the OAM multiplexed continuous variable entanglement, 9 OAM multiplexed channels of parallel all-optical quantum teleportation can be deterministically established in experiment. More importantly, our parallel all-optical quantum teleportation scheme can teleport OAM-superposition-mode coded coherent state, which demonstrates the teleportation of more than one optical mode with fidelity beating the classical limit and thus ensures the increase of information transmission capacity. Our results open the avenue for deterministically implementing parallel quantum communication protocols and provide a promising paradigm for constructing high-capacity all-optical quantum communication networks.

Observation of the interplay between seeded and self-seeded nondegenerate four-wave mixing in cesium vapor

Nondegenerate four-wave mixing (NFWM) is a practical and effective technique for generating or amplifying light fields at different wavelengths, and could be used to create color correlation and entanglement. Here we experimentally investigate the NFWM process in diamond atomic system via two-photon excitation with two pumps at 852 nm and 921 nm, demonstrating that a seeded NFWM with a third laser at 895 nm and two self-seeded NFWMs due to amplified spontaneous emission (ASE) occur simultaneously. We compare the two kinds of processes and show that the single- and two-photon detunings hold the key role in distinguishing them. As a result, the enhancement of seeded NFWM is obtained by selecting large one- and two-photon detunings, in which case the ASE induced self-seeded NFWM can be largely suppressed. In contrast, the ASE and its induced NFWM are effectively achieved with one- and two-photon resonant excitations allowing for population inversion for efficient ASE.

Polarization-Encrypted Orbital Angular Momentum Multiplexed Metasurface Holography

Metasurface holography has the advantage of realizing complex wavefront modulation by thin layers together with the progressive technique of computer-generated holographic imaging. Despite the well-known light parameters, such as amplitude, phase, polarization, and frequency, the orbital angular momentum (OAM) of a beam can be regarded as another degree of freedom. Here, we propose and demonstrate orbital angular momentum multiplexing at different polarization channels using a birefringent metasurface for holographic encryption. The OAM selective holographic information can only be reconstructed with the exact topological charge and a specific polarization state. By using an incident beam with different topological charges as erasers, we mimic a super-resolution case for the reconstructed image, in analogy to the well-known STED technique in microscopy. The combination of multiple polarization channels together with the orbital angular momentum selectivity provides a higher security level for holographic encryption. Such a technique can be applied for beam shaping, optical camouflage, data storage, and dynamic displays.

Deterministic Generation of Orbital-Angular-Momentum Multiplexed Tripartite Entanglement

We demonstrate the experimental generation of orbital angular momentum (OAM) multiplexed multipartite entanglement with cascaded four-wave mixing processes in a continuous variable (CV) system. In particular, we implement the simultaneous generation of 9 sets of OAM multiplexed tripartite entanglement over 27 Laguerre-Gauss (LG) modes, as well as 20 sets of OAM multiplexed bipartite entanglement over 40 LG modes, which show the rich entanglement structure of the system. In addition, we also generate tripartite entanglement of three types of coherent OAM superposition modes. Such OAM multiplexed multipartite entanglement opens the avenue to construct CV parallel quantum network for realizing parallel quantum information protocols.

Highly efficient vortex four-wave mixing in asymmetric semiconductor quantum wells

Orbital angular momentum (OAM) is an important property of vortex light, which provides a valuable tool to manipulate the light-matter interaction in the study of classical and quantum optics. Here we propose a scheme to generate vortex light fields via four-wave mixing (FWM) in asymmetric semiconductor quantum wells. By tailoring the probe-field and control-field detunings, we can effectively manipulate the helical phase and intensity of the FWM field. Particularly, when probe field and control field have identical detuning, we find that both the absorption and phase twist of the generated FWM field are significantly suppressed. Consequently, the highly efficient vortex FWM is realized, where the maximum conversion efficiency reaches around 50%. Our study provides a tool to transfer vortex wavefronts from input to output fields in an efficient way, which may find potential applications in solid-state quantum optics and quantum information processing.

Super-sensitive measurement of angular rotation displacement based on the hybrid interferometers

We theoretically study the angular rotation displacement based on the hybrid interferometers, which contain a beam splitter (BS) and an optical parameter amplication (OPA) for beam splitting and recombination. Two schemes with different orders of an OPA and a BS are discussed and both of them can realize the super resolving and sensitive angular rotation displacement. The sensitivity of angular rotation displacement can surpass the shot noise limit 12l N with the orbital angular momentum input beams. The squeezing strength of an OPA and the reflectivity of the BS play a decisive role on the resolutions and sensitivities while the losses play a negative effect on the sensitivity.

Ultraslow vortex four-wave mixing via multiphoton quantum interference

Orbital angular momentum (OAM) light is nowadays an intriguing resource in classical and quantum optics due to the richness of physical properties it shows in interaction with matter. A key ingredient needed to exploit the full potential of OAM light is the control of quantum interference, a crucial resource in fields like quantum communication and quantum optics. Here, we study the vortex four-wave mixing (FWM) via multi-photon quantum interference in an ultraslow propagation regime. We find that the structured information can be manipulated via two-photon detuning and three photon detuning, which manifests itself as a spatial modulation. The detailed explanations based on the dispersion relation are given, which are in good agreement with our simulations. Furthermore, in order to clearly show the modulated mechanism, we perform the interference between the FWM field and a same-frequency Gaussian beam. It is found that the interference patterns are also manipulated by adjusting the multi-photon detunings. This work may have some potential applications in quantum control based on OAM light.