Linear Optical Elements Research Articles

Efficient Entanglement Concentration of Nonlocal Two-Photon Polarization-Time-Bin Hyperentangled States

We present two different hyperentanglement concentration protocols (hyper-ECPs) for two-photon systems in nonlocal polarization-time-bin hyperentangled states with known parameters, including Bell-like and cluster-like states, resorting to the parameter splitting method. They require only one of two parties in quantum communication to operate her photon in the process of entanglement concentration, not two, and they have the maximal success probability. They work with linear optical elements and have good feasibility in experiment, especially in the case that there are a big number of quantum data exchanged as the parties can obtain the information about the parameters of the nonlocal hyperentangled states by sampling a subset of nonlocal hyperentangled two-photon systems and measuring them. As the quantum state of photons in the time-bin degree of freedom suffers from less noise in an optical-fiber channel, these hyper-ECPs may have good applications in practical long-distance quantum communication in the future.

Self-error-rejecting photonic qubit transmission in polarization-spatial modes with linear optical elements

We present an original self-error-rejecting photonic qubit transmission scheme for both the polarization and spatial states of photon systems transmitted over collective noise channels. In our scheme, we use simple linear-optical elements, including half-wave plates, 50:50 beam splitters, and polarization beam splitters, to convert spatial-polarization modes into different time bins. By using postselection in different time bins, the success probability of obtaining the uncorrupted states approaches 1/4 for single-photon transmission, which is not influenced by the coefficients of noisy channels. Our self-error-rejecting transmission scheme can be generalized to hyperentangled N-photon systems and is useful in practical high-capacity quantum communications with photon systems in two degrees of freedom.

Hyperentanglement concentration for polarization–spatial–time-bin hyperentangled photon systems with linear optics

Hyperentanglement has significant applications in quantum information processing. Here we present an efficient hyperentanglement concentration protocol (hyper-ECP) for partially hyperentangled Bell states simultaneously entangled in polarization, spatial-mode and time-bin degrees of freedom (DOFs) with the parameter-splitting method, where the parameters of the partially hyperentangled Bell states are known to the remote parties. In this hyper-ECP, only one remote party is required to perform some local operations on the three DOFs of a photon, only the linear optical elements are considered, and the success probability can achieve the maximal value. Our hyper-ECP can be easily generalized to concentrate the N-photon partially hyperentangled Greenberger–Horne–Zeilinger states with known parameters, where the multiple DOFs have largely improved the channel capacity of long-distance quantum communication. All of these make our hyper-ECP more practical and useful in high-capacity long-distance quantum communication.

Hyperentanglement concentration of nonlocal two-photon six-qubit systems with linear optics

Hyperentanglement, the entangled states in the multiple degrees of freedom (DOFs) of a photon system simultaneously, has attracted much attention recently as it can increase the capacity of quantum communication largely. Here we present the first scheme for concentrating the nonlocal two-photon six-qubit systems entangled in polarization, spatial-mode, and time-bin DOFs with linear optics. We construct the parity-check gates for the quantum states of nonlocal photon systems in all the three DOFs with linear-optical elements. Fortunately, our parity-check gate for one DOF does not affect the quantum states in the other two DOFs, which makes our hyperentanglement concentration protocol (hyper-ECP) can be implemented conveniently for polarization–spatial–time-bin partially hyperentangled states. This hyper-ECP is practical as it requires only linear-optical elements, and it can be directly generalized to improve the entanglement of nonlocal multi-photon systems entangled in three DOFs in the long-distance high-capacity quantum communication.

Fault-tolerant distribution of GHZ states and controlled DSQC based on parity analyses.

Based on the circuit including linear optical elements, a fault-tolerant distribution of GHZ states against collective noise among three parties is proposed. Additionally, two controlled DSQC protocols using the shared GHZ states as quantum channels are also presented under the charge of the controller. The first controlled DSQC protocol applies single parity analysis based on weak cross-Kerr nonlinearities. The receiver Bob performs single-photon measurement to obtain the secret information after the outcome publication of the single parity analysis executed by the sender Alice. The second protocol applies dense coding to double information transmission capacity, and the double parity analyses based on weak cross-Kerr nonlinearities are performed to obtain the secret information.

Generation of an arbitrary four-photon polarization-entangled decoherence-free state with cross-Kerr nonlinearity

We present a new scheme to provide an arbitrary four-photon polarization-entangled state, which enables the encoding of single logical qubit information into a four-qubit decoherence-free subspace robustly against collective decoherence. With the assistance of the cross-Kerr nonlinearities, a spatial entanglement gate and a polarization entanglement gate are inserted into the circuit, where the X-quadrature homodyne measurement is properly performed. According to the outcomes of homodyne measurement in the spatial entanglement process, some swap gates are inserted into the corresponding paths of the photons to swap their spatial modes. Apart from Kerr media, some basic linear optical elements are necessary, which make it feasible with current experimental techniques.

Experimental implementation of a quantum walk on a circle with single photons

We experimentally implement a quantum walk on a circle in position space. Using a different arrangement of linear optical elements, our experiment realizes clockwise-cycling and counterclockwise-cycling walks. Periodic evolutions in quantum walks on three- and four-node circles with uniform coin flipping for each step and a localized initial walker state are observed, and the full revival of the walker+coin state occurs. Coherent information encoded in the coin state shows the periodic collapse and revival due to the interaction between the coin and walker. The technology to realize clockwise-cycling and counterclockwise-cycling walks can be expanded to simulate a quantum walk on a circle with arbitrary nodes.

Practical entanglement concentration of nonlocal polarization-spatial hyperentangled states with linear optics

We present some different hyperentanglement concentration protocols (hyper-ECPs) for nonlocal N-photon systems in partially polarization-spatial hyperentangled states with known parameters, resorting to linear optical elements only, including those for hyperentangled Greenberger---Horne---Zeilinger-class states and the ones for hyperentangled cluster-class states. Our hyper-ECPs have some interesting features. First, they require only one copy of nonlocal N-photon systems and do not resort to ancillary photons. Second, they work with linear optical elements, neither Bell-state measurement nor two-qubit entangling gates. Third, they have the maximal success probability with only a round of entanglement concentration, not repeating the concentration process some times. Fourth, they resort to some polarizing beam splitters and wave plates, not unbalanced beam splitters, which make them more convenient in experiment.

One-photon controlled two-photon not gate contributed by weak cross-Kerr nonlinearities

A quantum logic gate is an indispensable fundamental element for completing tasks of quantum information processing, such as quantum computation and scalable quantum networks. With the help of weak cross-Kerr nonlinearities, we propose an efficient optical one-photon controlled two-photon not gate, where polarization modes of photons act as quantum bits, aiming to construct the practical and scalable quantum logic circuits. By adopting one-time nondestructive measurement, this gate can realize the function of two two-photon controlled-not gates, where the polarization bits of two target photons will be flipped when the controlled photon is in the vertical polarization state. After measuring on the coherent state, the suitable operations including swapping of photon states and single-photon transformations are carried out by classical feed forward, conditioned on the measurement outcomes. Simple linear optical elements, and mature techniques containing Homodyne measurement and classical feed forward are applied to enhance the feasibility of the scheme presented here and other scalable logic gates.

Universal Three-Qubit Entanglement Generation Based on Linear Optical Elements and Quantum Non-Demolition Detectors

Recently, entanglement plays an important role in quantum information science. Here we propose an efficient and applicable method which transforms arbitrary three-qubit unknown state to a maximally entangled Greenberger-Horne-Zeilinger state, and the proposed method could be further generalized to multi-qubit case. The proposed setup exploits only linear optical elements and quantum non-demolition detectors using cross-Kerr media. As the quantum non-demolition detection could reveal us the output state of the photons without destroying them. This property may make our proposed setup flexible and can be widely used in current quantum information science and technology.

Generation of four-photon polarization entangled decoherence-free states with cross-Kerr nonlinearity.

We propose a theoretical protocol for preparing four-photon polarization entangled decoherence-free states, which are immune to the collective noise. With the assistance of the cross-Kerr nonlinearities, a two-photon spatial entanglement gate, two controlled-NOT gates, a four-photon polarization entanglement gate are inserted into the circuit, where X homodyne measurements are aptly applied. Combined with some swap gates and simple linear optical elements, four-photon polarization entangled decoherence-free states which can be utilized to represent two logical qubits, |0〉L and |1〉L are achieved at the output ports of the circuit. This generation scheme may be implemented with current experimental techniques.

Efficient Preparation and Nondestructive Analysis of Photon and Spin Entangled States with Double-Sided Cavity and Nitrogen-Vacancy Center Coupled System

In this paper, we study the preparation and nondestructive analysis of photon and spin entangled states with double-sided cavity and nitrogen-vacancy center coupled system, which is efficient in weak-coupling regime. The setups are based on some simple linear optical elements, delay lines and conventional photon detectors, which are feasible with existing experimental technology. Numerical simulation demonstrates that all protocols’ fidelities and successful probabilities are high in principle. Therefore, our protocols may be useful for decreasing the experimental requirements for preparation and nondestructive analysis of entangled states.

Preparation of four-photon polarization-entangled decoherence-free states employing weak cross-Kerr nonlinearities

With the assistance of weak cross-Kerr nonlinearities, we present a preparation scheme of four-photon polarization-entangled decoherence-free states, which can be used to construct the minimal optical decoherence-free subspaces where a logical qubit is fully protected against collective decoherence. To complete the preparation task, one spatial entanglement process, two polarization entanglement processes, and one detecting process are applied. The fulfillments of the above processes are contributed by a cross-Kerr nonlinear interaction between the signal photons and a coherent state via Kerr media. Exploiting the available single-photon resource and simple linear optics elements, this scheme is feasible and desirable to be extended to the construction of multiphoton decoherence-free states against the collective decoherence.

Fully integrated quantum photonic circuit with an electrically driven light source

Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices. Single photons are generated from electrically driven semiconducting single-walled carbon nanotubes embedded in a photonic circuit. Pronounced antibunching is observed when photon correlation is measured at cryogenic temperatures.

On unitary reconstruction of linear optical networks

Linear optical elements are pivotal instruments in the manipulation of classical and quantum states of light. Recent progress in integrated quantum photonic technology enabled the implementation of large numbers of such elements on chip, in particular passively stable interferometers. However, it is a challenge to characterize the optical transformation of such a device as the individual optical elements are not directly accessible. Thus only an effective overall transformation can be recovered. Here we present a reconstruction approach based on a global optimization of element parameters and compare it to two prominently used approaches. We numerically evaluate their performance for networks up to 14 modes and various levels of error on the primary data.

Quantum homomorphic signature based on Bell-state measurement

In this paper, a novel quantum homomorphic signature scheme based solely on Bell-state measurement is proposed. It allows an aggregator to merge two signature nodes' signatures of their classical messages into one signature, which is an effective approach to identity authentication for multiple streams to enhance the security of quantum networks. And it is easy to generalize this scheme to multiple nodes. Bell-state measurement has been realized by using only linear optical elements in many experimental measurement-device-independent quantum key distribution schemes, which makes us believe that our scheme can be realized in the near future. It is shown that our scheme is a quantum group homomorphic signature scheme and is secure by the scheme analysis.

Quantum Private Comparison Protocol with Linear Optics

In this paper, we propose an innovative quantum private comparison(QPC) protocol based on partial Bell-state measurement from the view of linear optics, which enabling two parties to compare the equality of their private information with the help of a semi-honest third party. Partial Bell-state measurement has been realized by using only linear optical elements in experimental measurement-device-independent quantum key distribution(MDI-QKD) schemes, which makes us believe that our protocol can be realized in the near future. The security analysis shows that the participants will not leak their private information.

Two-photon phase gate with linear optical elements and atom–cavity system

We propose a protocol for implementing $$\pi $$ź phase gate of two photons with linear optical elements and an atom---cavity system. The evolution of the atom---cavity system is based on the quantu...

Hollow Gaussian beam generation through nonlinear interaction of photons with orbital angular momentum.

Hollow Gaussian beams (HGB) are a special class of doughnut shaped beams that do not carry orbital angular momentum (OAM). Such beams have a wide range of applications in many fields including atomic optics, bio-photonics, atmospheric science, and plasma physics. Till date, these beams have been generated using linear optical elements. Here, we show a new way of generating HGBs by three-wave mixing in a nonlinear crystal. Based on nonlinear interaction of photons having OAM and conservation of OAM in nonlinear processes, we experimentally generated ultrafast HGBs of order as high as 6 and power >180 mW at 355 nm. This generic concept can be extended to any wavelength, timescales (continuous-wave and ultrafast) and any orders. We show that the removal of azimuthal phase of vortices does not produce Gaussian beam. We also propose a new and only method to characterize the order of the HGBs.

Joint remote preparation of arbitrary two- and three-photon state with linear-optical elements

In this paper, two schemes for joint remote preparation via linear optics elements are proposed. Firstly, we propose a scheme for joint remote preparation of an arbitrary two-photon state via linear-optical elements by using a five-qubit cluster state as the quantum channel. Then, the JRSP protocol of an arbitrary three-photon state via linear-optical elements, which was rarely considered in previous papers, is investigated. All the senders share the information of prepared state. The senders transform the quantum channel to the target quantum channel according to their information of prepared state, and the receiver can prepare the original state by performing corresponding operations on his entangled particles. Our scheme has advantage of transmitting less particles for joint remote preparing an arbitrary two-qubit state. Moreover, it is more convenience in application since it only requires linear-optical elements for joint remote preparation.