Quantum teleportation faces increasingly demanding requirements for transmitting large or even entangled systems. However, knowledge of the state to be transmitted eases its reconstruction, resulting in a protocol known as remote state preparation. A number of experimental demonstrations to date have been restricted to single-qubit systems. We report the remote preparation of two-qubit "hybrid" entangled states, including a family of vector-polarization beams. Our single-photon states are encoded in the photon spin and orbital angular momentum. We reconstruct the states by spin-orbit state tomography and transverse polarization tomography. The high fidelities achieved for the vector-polarization states opens the door to optimal coupling of down-converted photons to other physical systems, such as an atom, as required for scalable quantum networks, or plasmons in photonic nanostructures.
Quantum teleportation faces increasingly demanding requirements for transmitting large or even entangled systems. However, knowledge of the state to be transmitted eases its reconstruction, resulting in a protocol known as remote state preparation. A number of experimental demonstrations to date have been restricted to single-qubit systems. We report the remote preparation of two-qubit "hybrid" entangled states, including a family of vector-polarization beams. Our single-photon states are encoded in the photon spin and orbital angular momentum. We reconstruct the states by spin-orbit state tomography and transverse polarization tomography. The high fidelities achieved for the vector-polarization states opens the door to optimal coupling of down-converted photons to other physical systems, such as an atom, as required for scalable quantum networks, or plasmons in photonic nanostructures.
There exists two prominent methods to transfer information between two spatially separated parties, namely Alice (A) and Bob (B): quantum teleportation and remote state preparation. However, the difference between these methods is, in the teleportation scheme, the state to be transferred is completely unknown, whereas in state preparation it should be known to the sender. In addition, photonic state teleportation is probabilistic due to the impossibility of performing a two-particle complete Bell-state analysis with linear optics, while remote state preparation can be performed deterministically. Here we report the first realization of photonic hybrid remote state preparation from spin to orbital angular momentum degrees of freedom. In our scheme, the polarization state of photon A is transferred to orbital angular momentum of photon B. The prepared states are visualized in real time by means of an intensified CCD camera. The quality of the prepared states is verified by performing quantum state tomography, which confirms an average fidelity higher than 99.4%. We believe that this experiment paves the way towards a novel means of quantum communication in which encryption and decryption are carried out in naturally different Hilbert spaces, and therefore may provide a means for enhancing security.
Remote state preparation is a fundamental quantum-information protocol that exploits prior knowledge of a target state to reduce the communication resources required for quantum-state distribution. Here, we propose a remote-state-preparation protocol for a stationary electron-spin qubit using hybrid entanglement between the electron spin and a coherent-state light pulse, generated by spin-dependent reflection from a spin-cavity system. Unlike single-photon encodings, the coherent-state encoding is naturally tolerant of photon loss: a loss channel attenuates the coherent-state amplitude, leading to a gradual reduction in preparation fidelity rather than probabilistic protocol failure. The central difficulty---implementing the projection onto superpositions of nonorthogonal coherent states required in the conventional protocol---is circumvented by coupling the transmitted pulse to an auxiliary spin, followed by homodyne detection and a spin projective measurement. The protocol therefore avoids direct coherent-state-superposition measurements and photon-number-resolving detection. In the ideal limit, deterministic preparation of a particular class of target states can be achieved using only one bit of classical communication. We analytically quantify the effects of coherent-state nonorthogonality, fiber loss, and spin dephasing on the preparation fidelity. Increasing the coherent-state amplitude improves state distinguishability and hence the preparation fidelity, but also enhances which-branch information leakage caused by photon loss, resulting in an optimal amplitude at each transmission distance. For experimentally relevant parameters, the optimized average fidelity remains well above the classical benchmark over distances of tens of kilometers. We also discuss a possible implementation using diamond nitrogen-vacancy centers.
We present a technique for remotely preparing an arbitrary single-photon hybrid state between two distant nodes. This remote state preparation (RSP) is accomplished with a hyper-entangled state in polarization and time-bin degrees of freedom (DoFs) using some experimentally available optical elements and devices. In our RSP, the sender performs unitary operations on her hyper-entangled photon in accordance with her knowledge of the desired state to be transmitted. By performing a single-photon projective measurement and classical communication, the target state will be reconstructed at the remote receiver’s quantum system. Furthermore, we discuss the RSP via a partially hyper-entangled state. We expect our study can pave the way towards the investigation of long-distance quantum communication scenarios.
The thesis introduces two single-photon experiments with the lattice of spin-orbit arrays. The basic background knowledge has been introduced in Chapter 1. Chapters 2-4 describe the detailed techniques used in these two experiments. \n \nIn the first work, we implement a remote state preparation protocol on our single-photon orbital angular momentum (OAM) lattice state via hybrid-entanglement. Remote state preparation is a variant of quantum state teleportation where the sender knows the transmitted state. It is known to require fewer classical resources and exhibit a nontrivial trade-off between the entanglement and classical communication compared with quantum teleportation. Here we propose a state preparation scheme between two spatially separated photons sharing a hybrid-entangled polarization-OAM state. By sending one of the polarization-entangled photon pairs through Lattice of Optical Vortex prism pairs, we generate a two-dimensional lattice of spin-orbit coupled single-photons. We show that the measurement taken by an electron-multiplying intensified CCD camera on the transformed photons can be remotely prepared by the polarization projection of the other. Our protocol could have a significant impact on long-distance quantum communication with higher channel capacity and lead to more efficient and compatible quantum information processing techniques. \n \nThe second experiment investigates the single-photon Talbot Effect in spin-orbit arrays. The Talbot Effect is a near-field diffraction effect, that occurs with the propagation of periodically structured waves. It has enabled several unique applications in optical metrology, image processing, data transmission, and matter-wave interferometry. We observe that upon propagation, the wavefronts of the single photons manifest self-imaging whereby the OAM lattice intensity profile is recovered. Furthermore, we show that the intensity distribution at each fractional Talbot distance is indicative of the periodic helical phase structure corresponding to a lattice of OAM states. This phenomenon is a significant addition to the toolbox of orbital angular momentum and spin-orbit techniques that are becoming increasingly important in optical implementations of quantum information.
Linear-optical-based quantum information processing has attached much attention since photon is an ideal medium for transmitting quantum information remotely. Until now, there are some important works in quantum state remote preparation, the method for reconstructing quantum state deterministically via linear optics. However, most of the methods are protocols to prepare single-qubit states remotely via linear-optical elements. In this article, we investigate the methods to prepare two-qubit hybrid states remotely. We present a deterministic remote state preparation scheme for an arbitrary two-qubit hybrid state via a hyperentangled Bell state, resorting to linear-optical elements only. The sender rotates the spatial-mode state and polarization state of the hyperentangled photon respectively in accordance with his knowledge of the two-qubit hybrid state, and the receiver can reconstruct the original two-qubit hybrid state by applying appropriate recovery operations. Moreover, we discuss the remote state preparation scheme for the two-qubit hybrid state via partially hyperentangled Bell state.
We study the quantum communication protocol of remote state preparation (RSP) for pure states of qubits encoded in single photons transmitted through a double slit, the so-called spatial qubits. Two measurement strategies that one can adopt to remotely prepare the states are discussed. The first strategy is the well-known spatial postselection, where a single-pixel detector measures the transverse position of the photon between the focal and the image plane of a lens. The second strategy, proposed by ourselves, is a generalized measurement divided into two steps: the implementation of a two-outcome positive operator-valued measurement (POVM) followed by the spatial postselection at the focal plane of the lens by a two-pixel detector in each output of the POVM. In both cases we analyze the effects of the finite spatial resolution of the detectors over three figures of merit of the protocol, namely, the probability of preparation, the fidelity, and purity of the remotely prepared states. It is shown that our strategy improves these figures compared with spatial postselection, at the expense of increasing the classical communication cost as well as the required experimental resources. In addition, we present a modified version of our strategy for RSP of spatial qudits which is able to prepare arbitrary pure states, unlike spatial postselection alone. We expect that our study may also be extended for RSP of the angular spectrum of a single-photon field as an alternative for quantum teleportation which requires very inefficient nonlinear interactions.