The laws of quantum mechanics enable optical communications with the ultimate capacity and quantum computers to solve certain problems with unprecedented speed. A key ingredient in such quantum information processing is quantum teleportation: the act of transferring quantum information from a sender to a spatially distant receiver by utilizing shared entanglement and classical communications. For example, optical quantum teleportation is essential for various quantum communication protocols. Quantum logic gates based on optical quantum teleportation are one of the building blocks of optical quantum computers.
The laws of quantum mechanics enable optical communications with the ultimate capacity and quantum computers to solve certain problems with unprecedented speed. A key ingredient in such quantum information processing is quantum teleportation: the act of transferring quantum information from a sender to a spatially distant receiver by utilizing shared entanglement and classical communications. For example, optical quantum teleportation is essential for various quantum communication protocols. Quantum logic gates based on optical quantum teleportation are one of the building blocks of optical quantum computers.
Quantum teleportation is a transfer protocol of quantum states, which cannot be realized only with classical physics. The essence of this protocol is quantum entanglement, which was proposed by Einstein as a counter example for quantum mechanics. In terms of quantum information processing, quantum teleportation can be regarded as an “Identity” operation. So one can modify the quantum circuit to make an arbitrary operation and universal quantum computing. One of the application of the quantum computing is “quantum version of coherent communication”, which enables us to get the channel capacity beyond the classical limit (Shannon limit).
Summary form only given. Quantum teleportation is a technique via which the quantum state of a system can be reconstructed at a distant station through the direct transmission of only classical information. This remarkable effect is made possible by the sharing of a nonlocally entangled state by the sender and receiver, constituting an indirect quantum channel. Teleportation has applications in quantum computing and general quantum information manipulation. Teleportation of optical fields holds great promise due to the power of the required optical tools and the maturity of relevant optical communications technology. Recently, a high efficiency, experimental demonstration of the continuous variable teleportation of a single mode, coherent optical field has been made.
Quantum teleportation allows for the transfer of arbitrary, in principle, unknown quantum states from a sender to a spatially distant receiver, who share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. In order to realize flying qubits in these schemes, photons are an optimal choice. However, teleporting a photonic qubit has been limited due to experimental inefficiencies and restrictions. Major disadvantages have been the probabilistic nature of both entangled resource states and linear-optics Bell-state measurements (BSM), as well as the need for post-selecting the successful events by destroying the teleported qubit. Here, all the above limitations are overcome through a totally distinct, “hybrid” approach: continuous-variable (CV) quantum teleportation of a discrete-variable, photonic qubit. The strength of CV teleportation lies in the on-demand availability of the quadrature-entangled states and the completeness of a BSM in the quadrature bases using linear optics and homodyne detections; this enables fully deterministic, unconditional teleportation of photonic qubits. We implement this kind of “hybrid” teleportation by utilizing a very recent, advanced technology: a broadband CV teleporter and a narrow-band qubit compatible with the teleporter.
A remarkable application of quantum mechanical concepts of coherent superposition and quantum entanglement is a quantum computer which can solve certain problems at speeds unbelievably faster than the conventional computer. In this chapter, the basic principles and the conditions for the implementation of the quantum computer are introduced and the limitations imposed by the probabilistic nature of quantum mechanics and the inevitable decoherence phenomenon are discussed. Next the basic building blocks, the quantum logic gates, are introduced. These include the Hadamard, the CNOT, and the quantum phase gates. After these preliminaries, the implementation of the Deutsch algorithm, quantum teleportation, and quantum dense coding in terms of the quantum logic gates are discussed. It is also shown how the Bell states can be produced and measured using a sequence of quantum logic gates.
Present information technology is based on the laws of classical physics. However, advances in quantum physics have stimulated interest in its potential impact on such technology. This article is an introductory review of three aspects of quantum information processing, cryptography, computation, and teleportation. The author serves up hors d'oeuvres on the relevant parts of quantum physics and the sorts of quantum systems which might form the building blocks for quantum processors. Quantum cryptography utilizes states of individual quantum systems for the transfer of conventional classical bits of information. The impossibility of measuring quantum systems without disturbing them guarantees the detection of eavesdropping and hence secure information transfer is possible. In a sense, teleportation is the inverse of cryptography, using more robust classical bits to faithfully transfer a quantum state through a noisy environment. Quantum computation utilizes the evolving quantum state of a complex system, which consists of many interacting individuals. If such a machine could be built, it would be capable of solving some problems which are intractable on any conventional computer; he illustrates this with Shor's (see Proc. 35th IEEE Symposium on Foundations of Computer Science, p.124, 1994) quantum factoring algorithm. Details are given of the current experimental achievements, proposals, and prospects for the future and of the patents granted to date.
In recent years, there has been heightened interest in quantum teleportation, which allows for the transfer of unknown quantum states over arbitrary distances. Quantum teleportation not only serves as an essential ingredient in long-distance quantum communication, but also provides enabling technologies for practical quantum computation. Of particular interest is the scheme proposed by D. Gottesman and I. L. Chuang [(1999) Nature 402:390-393], showing that quantum gates can be implemented by teleporting qubits with the help of some special entangled states. Therefore, the construction of a quantum computer can be simply based on some multiparticle entangled states, Bell-state measurements, and single-qubit operations. The feasibility of this scheme relaxes experimental constraints on realizing universal quantum computation. Using two different methods, we demonstrate the smallest nontrivial module in such a scheme--a teleportation-based quantum entangling gate for two different photonic qubits. One uses a high-fidelity six-photon interferometer to realize controlled-NOT gates, and the other uses four-photon hyperentanglement to realize controlled-Phase gates. The results clearly demonstrate the working principles and the entangling capability of the gates. Our experiment represents an important step toward the realization of practical quantum computers and could lead to many further applications in linear optics quantum information processing.